Name: ___________________________ Class: _________________ Date: __________
Chapter 01 1. Living systems are incredibly diverse in size, shape, environment, and behavior. It is estimated that there are between 10 million and 100 million different species. Despite this wide variety of organisms, it remains difficult to define what it means to say something is alive. Which of the following can be described as the smallest living unit? a. DNA b. cell c. organelle d. protein
2. The central dogma provides a framework for thinking about how genetic information is copied and used to produce structural and catalytic components of the cell. From the choices below, select the order of components and biochemical processes that best correlates with the tenets of the central dogma. a. DNA [transcription] RNA [translation] protein b. protein [translation] RNA [transcription] DNA c. DNA [translation] RNA [transcription] protein d. RNA [transcription] protein [translation] DNA
3. Proteins are important architectural and catalytic components within the cell, helping to determine its chemistry, shape, and ability to respond to changes in the environment. Remarkably, all the different proteins in a cell are made from the same 20 __________. By linking them in different sequences, the cell can make protein molecules with different conformations and surface chemistries, and therefore different functions. a. nucleotides b. sugars c. amino acids d. fatty acids
4. Which statement is FALSE about mutations? a. A mutation is a change in the DNA that can generate offspring less fit for survival than their parents. b. A mutation can be a result of imperfect DNA replication. c. A mutation is a result of sexual reproduction. d. A mutation is a change in the DNA that can generate offspring that are as fit for survival as their parents are.
5. Changes in DNA sequences from one generation to the next may result in offspring that are altered in fitness compared with their parents. The process of change and selection over the course of many generations is the basis of a. mutation. b. evolution. c. heredity. d. reproduction.
6. Select the option that best finishes the following statement: Evolution is a process a. that can be understood based on the principles of mutation and selection. b. that results from repeated cycles of adaptation over billions of years. c. by which all present-day cells arose from four to five different ancestral cells. d. that requires hundreds of thousands of years.
7. A cell’s genome a. is defined as all the genes being used to make protein. b. contains all of a cell’s DNA. c. constantly changes, depending upon the cell’s environment. d. is altered during embryonic development.
8. Which statement is FALSE about the events/conclusions from studies during the mid-1800s surrounding the discovery of cells? a. Cells came to be known as the smallest universal building block of living organisms.
b. Scientists concluded that new cells can form spontaneously from the remnants of ruptured cells. c. Light microscopy was essential in demonstrating the commonalities between plant and animal tissues. d. New cells arise from the growth and division of previously existing cells.
9. What unit of length would you generally use to measure a typical plant or animal cell? a. centimeters b. nanometers c. millimeters d. micrometers
10.Cell biologists employ targeted fluorescent dyes or modified fluorescent proteins in both standard fluorescence microscopy and confocal microscopy to observe specific details in the cell. Even though fluorescence permits better visualization, the resolving power is essentially the same as that of a standard light microscope because the resolving power of a fluorescent microscope is limited by the __________ of visible light. a. absorption b. intensity c. filtering d. wavelength
11.What is the smallest distance two points can be separated and still resolved using light microscopy? a. 20 nm b. 0.2 μm c. 2 μm d. 200 μm
12.Which of the following reagents should you recommend to your colleague if she is attempting to add contrast to a specimen that she intends to prepare for transmission electron microscopy?
a. fluorescein b. formaldehyde c. osmium tetroxide d. methylene blue
13.Prokaryotic cells do not possess a. a nucleus. b. replication machinery. c. ribosomes. d. membrane bilayers.
14.Which three characteristics best support the rapid evolution of prokaryotic populations? a. microscopic, motile, anaerobic b. aerobic, motile, rapid growth c. no organelles, cell wall, can exchange DNA d. large population, rapid growth, can exchange DNA
15.The world of prokaryotes is divided into two domains (bacteria and archaea), each as different from the other as from eukaryotes. Select the observable characteristic that best distinguishes archaea from bacteria. a. can metabolize inorganic substances b. are found in extremely harsh environments c. thrive in anaerobic conditions d. are photosynthetic organisms
16.After 12 years of painstaking work, researchers managed to grow in a laboratory bioreactor an archaeon species that belongs to the lineage of archaea with the most eukaryotic-like genes. Which of the following characteristics of this organism is most relevant to our understanding of the evolution of eukaryotes? a. cellular protrusions extending from the cell body b. native to hydrothermal vents on the ocean floor c. required methane gas for growth in bioreactor
d. originally identified off the coast of Greenland
17.The __________ is made up of two concentric membranes and is continuous with the membrane of the endoplasmic reticulum. a. plasma membrane b. Golgi network c. mitochondrial membrane d. nuclear envelope
18.The nucleus, an organelle found in eukaryotic cells, confines the __________, keeping them separated from other components of the cell. a. lysosomes b. chromosomes c. peroxisomes d. ribosomes
19.Which of the following organelles has both an outer and an inner membrane? a. endoplasmic reticulum b. mitochondrion c. lysosome d. peroxisome
20.Mitochondria perform cellular respiration, a process that uses oxygen, generates carbon dioxide, and produces chemical energy for the cell. Which answer below is a correct pairing of the material consumed with the form of energy produced during cellular respiration? a. fat, ADP b. sugar, fat c. sugar, ATP d. fat, protein
21.Mitochondria contain their own genome, can duplicate, and divide on a different
time line from the rest of the cell. Nevertheless, mitochondria cannot function for long when isolated from the cell because they are a. viruses. b. parasites. c. endosymbionts. d. anaerobes.
22.The mitochondrial proteins found in the inner membrane are involved in the conversion of ADP to ATP, a source of energy for the cell. This process consumes which of the following substances? a. oxygen b. nitrogen c. sulfur d. carbon dioxide
23.Chloroplasts are complex organelles present in all photosynthesizing eukaryotes. Three different membranes create chemically different environments inside the chloroplast. Precisely where are chlorophyll molecules localized within the chloroplast? a. the outer boundary membrane b. the space between the outer and inner boundary membranes c. the inner boundary membrane d. the internal (thylakoid) membrane
24.Photosynthesis enables plants to capture the energy from sunlight. In this essential process, plants incorporate the carbon from CO2 into high-energy __________ molecules that plant cell mitochondria use to produce ATP. a. fat b. sugar c. protein d. fiber
25.Which of the following best describes the role of the lysosome?
a. transport of material to the Golgi apparatus b. clean up, recycling, and disposal of macromolecules c. inactivation of toxic molecules via hydrogen peroxide d. storage of excess macromolecules
26.The cell constantly exchanges materials by bringing nutrients in from the external environment and shuttling unwanted by-products back out. Which term describes the process by which external materials are captured inside transport vesicles and brought into the cell? a. degradation b. exocytosis c. oxidation d. endocytosis
27.Eukaryotic cells can trigger the release of material from secretory vesicles to the extracellular space using a process called exocytosis. An example of materials commonly released this way is a. hormones. b. nucleic acids. c. sugars. d. cytosolic proteins.
28.__________ are small, membrane-bound organelles that provide a safe place within the cell to carry out biochemical reactions that generate and remove harmful, highly reactive oxygen species like superoxide and hydrogen peroxide. a. Vesicles b. Lysosomes c. Peroxisomes d. Endosomes
29.The cytoskeleton provides support, structure, motility, and organization, and it forms tracks to direct organelle and vesicle transport. Which of the cytoskeletal elements listed below is the thickest?
a. actin filaments b. microtubules c. intermediate filaments d. none of these (all have the same thickness)
30.Despite the differences between eukaryotic and prokaryotic cells, prokaryotes have proteins that are distantly related to eukaryotic actin filaments and microtubules. What is likely to be the most ancient function of the cytoskeleton? a. cell motility b. vesicle transport c. membrane support d. cell division
31.Choose the phrase that best completes the following sentence: Microtubules __________ and are required to pull duplicated chromosomes to opposite poles of dividing cells. a. generate contractile forces b. are intermediate in thickness c. can rapidly reorganize d. are found in especially large numbers in muscle cells
32.Which pair of values best fills in the blanks in the following statement? On average, eukaryotic cells are __________ times longer and have __________ times more volume than prokaryotic cells. a. 5; 100 b. 10; 200 c. 10; 100 d. 10; 1000
33.Cells that are specialized for the secretion of proteins are likely to have which of the following features? a. long bundles of actin/myosin proteins b. small volume of cytoplasm
c. large population of mitochondria d. enlarged endoplasmic reticulum
34.Which of the following would you expect to find in a cytosolic fraction prepared from cultured mammalian cells? a. mitochondrial enzymes b. ribosomal subunits c. photosynthetic membranes d. lysosomal proteins
35.Scientists learned that cell death is a normal and even important part of life by studying the development of the nematode worm Caenorhabditis elegans. What was the most important feature of C. elegans for the study of programmed cell death? a. The nematode is smaller and simpler than the fruit fly. b. Seventy percent of C. elegans genes have homologs in humans. c. The developmental pathway of each cell in the adult worm was known. d. Its genome was partially sequenced.
36.Biologists cannot possibly study all living species. Instead, they try to understand cell behavior by studying a select subset of species. Which of the following characteristics is/are useful in an organism chosen for use as a model in laboratory studies? a. amenability to genetic manipulation b. ability to grow under controlled conditions c. rapid rate of reproduction d. all of the above
37.Which species was the key model organism for the advancement of molecular biology (understanding DNA replication, decoding the DNA to make proteins, etc.)? a. E. coli b. D. melanogaster
c. S. cerevisiae d. C. elegans
38.A. thaliana, or Arabidopsis, is a common weed. Biologists have selected it over hundreds of thousands of other flowering plant species to serve as an experimental model organism because it a. can withstand extremely cold climates. b. can reproduce in 8–10 weeks. c. produces millions of offspring per plant. d. can be grown outdoors.
39.Drosophila melanogaster is a(n) __________. This type of animal is the most abundant of all animal species, making it an appropriate choice as an experimental model. a. insect b. bird c. amphibian d. mammal
40.C. elegans is a nematode. During its development, it produces more than 1000 cells. However, the adult worm has only 959 somatic cells. The process by which 131 cells are specifically targeted for destruction is called a. directed cell pruning. b. programmed cell death. c. autophagy. d. necrosis.
41.Zebrafish (Danio rerio) are especially useful in the study of early development because their embryos a. are exceptionally large. b. develop slowly. c. are transparent. d. are pigmented.
42.You wish to explore how mutations in specific genes affecting sugar metabolism might alter tooth development. Which organism is likely to provide the best model system for your studies? a. horses b. mice c. E. coli d. Arabidopsis
43.Scientists have observed all but one of the following outcomes in studies of human cells grown in tissue culture. Which outcome have they NOT observed? a. Cultured neurons extend axons that form functional connections with other cells. b. Epithelial cells join to form continuous sheets that mimic tissue layers inside the body. c. Cultured cells change their shape and/or behavior when exposed to hormones and growth factors. d. Embryonic cells differentiate into multiple cell types and produce fully functional organs that can be used for transplantation.
44.The SARS-CoV-2 virus that was responsible for the COVID-19 pandemic provides a great example of the value of genetic research to human health. Which of the following genetic findings about the SARS-CoV-2 virus was most directly responsible for the mask mandates common during the pandemic? a. The virus belongs to the coronavirus family of viruses. b. mRNAs encoding viral spike proteins elicit a robust immune response. c. Genome comparisons showed the virus spreads by asymptomatic carriers. d. The virus is a great model system for studying infectious particles.
45. The following figure shows an experiment conducted by Paul Nurse and colleagues to see if a cell division defect in S. pombe yeast cells could be fixed, or “rescued,” by adding the genetic material from closely related S. cerevisiae yeast cells. Study the figure carefully. What would you expect to happen if human DNA had been used instead of S. cerevisiae DNA? Why?
Figure 1-1 a. The plate would not contain any growth because human DNA is toxic to S. pombe yeast cells. b. The plate would contain a small number of S. pombe colonies because human DNA contains a gene that can rescue the defect in the yeast cells. c. The plate would not contain any colonies because human DNA is too different from yeast DNA to correct for the error in the yeast cells. d. The plate would be covered in numerous S. cerevisiae colonies because yeast cells proliferate spontaneously in the presence of foreign DNA.
46.Match each of the following types of microscopy with its corresponding description provided below. There is one best match for each. a. Confocal b. Transmission electron
c. Fluorescence d. Phase-contrast e. Scanning electron f. Bright-field 1. __________ uses a light microscope with an optical component to take advantage of the different refractive indices of light passing through different regions of the cell. 2. __________ employs a light microscope and requires that samples derived from thick tissues be fixed and stained in order to reveal cellular details. 3. __________ requires the use of two sets of filters. The first filter set narrows the wavelength range that reaches the specimen; the second blocks out all wavelengths that pass back up to the eyepiece except for those emitted by the dye in the sample. 4. __________ scans the specimen with a focused laser beam to obtain a series of two-dimensional optical sections that can be used to reconstruct an image of the specimen in three dimensions. The laser excites a fluorescent dye molecule, and the emitted light from each illuminated point is captured through a pinhole and recorded by a detector. 5. __________ can resolve cellular components as small as 2 nm. 6. __________ requires coating a sample with a thin layer of a heavy metal to produce three-dimensional images of the sample surface.
47.Match a structure from the list below (A–G) with the labels 1–7 in the schematic drawing of an animal cell in Figure 1-2.
Figure 1-2 a. plasma membrane
b. nuclear envelope c. cytosol d. Golgi apparatus e. endoplasmic reticulum f. mitochondrion g. transport vesicles 1. 1 2. 2 3. 3 4. 4 5. 5 6. 6 7. 7
48.Select all the cell types in which the listed structure or molecule can be found. Note that the structure or molecule can be found in more than one type of cell.
Figure 1-3 a. animal b. plant c. bacterial d. animal and plant e. plant and bacterial f. animal and bacterial g. animal, plant, and bacterial 1. DNA 2. nucleus 3. plasma membrane 4. chloroplast 5. cell wall
6. lysosome 7. mitochondrion 8. Golgi apparatus
49.For each of the following sentences, fill in the blanks with the best word or phrase selected from the list below. Not all words or phrases will be used, and each word or phrase should be used only once. Cells can be very diverse: superficially, they come in various sizes, ranging from bacterial cells such as Lactobacillus, which is a few _____1_____ in length, to larger cells such as a frog’s egg, which has a diameter of about 1 _____2_____. Despite the diversity, cells resemble each other to an astonishing degree in their chemistry. For example, the same 20 _____3_____ are used to make proteins. Similarly, the genetic information of all cells is stored in their _____4_____. Although _____5_____ contain the same types of molecules as cells, their inability to reproduce themselves by their own efforts means that they are not considered living matter. a. amino acids b. DNA c. fatty acids d. meter(s) e. micrometer(s) f. millimeter(s) g. plants h. plasma membranes i. viruses j. yeast 1. 1 2. 2 3. 3 4. 4 5. 5
50.Select the letter that corresponds to the specimen(s) that are best visualized with each of the microscopes listed below. Some specimens may be used more than once. a. live cells only b. fixed cells only c. both live and fixed cells
1. bright-field 2. phase-contrast 3. fluorescence 4. transmission electron
51.For each of the following sentences, fill in the blanks with the best word or phrase selected from the list below. Not all words or phrases will be used, and each word or phrase should be used only once. Eukaryotic cells are bigger and more elaborate than prokaryotic cells. By definition, all eukaryotic cells have a _____1_____, usually the most prominent organelle. Another organelle found in essentially all eukaryotic cells is the _____2_____, which generates the chemical energy for the cell. In contrast, the _____3_____ is a type of organelle found only in the cells of plants and algae; it performs photosynthesis. If we were to strip away the plasma membrane from a eukaryotic cell and remove all of its membrane-enclosed organelles, we would be left with the _____4_____, which contains many long, fine filaments of protein that are responsible for cell shape and structure, and thereby form the cell’s _____5_____. a. chloroplast b. chromosome c. cytoskeleton d. cytosol e. endoplasmic reticulum f. mitochondrion g. nucleus h. ribosomes 1. 1 2. 2 3. 3 4. 4 5. 5
52.Brewer’s yeast, apart from being an irreplaceable asset in the brewery and in the bakery, is an experimental organism used to study eukaryotic cells. However, it does have some limitations. Which of the processes can and cannot be studied in yeast? a. can be studied in yeast
b. cannot be studied in yeast 1. differentiation 2. motility 3. exocytosis 4. cell division
53.Number the following cells based on when they are believed to have evolved. a. 1 b. 2 c. 3 d. 4 e. 5 f. 6 1. anaerobic eukaryote 2. aerobic prokaryote 3. anaerobic prokaryote 4. photosynthetic eukaryote 5. aerobic eukaryote 6. photosynthetic prokaryote
54.Given what you know about the differences between prokaryotic cells and eukaryotic cells, rate the following biological processes as “unsuitable” or “suitable” for study using E. coli as the model organism. a. unsuitable b. suitable 1. formation of the endoplasmic reticulum 2. DNA replication 3. how the actin cytoskeleton contributes to cell shape 4. how cells decode their genetic instructions to make proteins 5. how mitochondria get distributed to cells during cell division
55.For each of the four processes in the table below, identify which one of the three model organisms would be the best choice for studying the process indicated. There is one correct model organism for each process.
Process
Model Organism
1 programmed cell death
E. coli
yeast
C. elegans
2
chloroplast function
C. elegans
Drosophila
Arabidopsis
3
immunology
mouse
Arabidopsis
yeast
Drosophila
E. coli
yeast
4 development of a multicellular tissue
a. E. coli b. yeast c. C. elegans d. Arabidopsis e. Drosophila f. mouse 1. programmed cell death 2. chloroplast function 3. immunology 4. development of a multicellular tissue
56.Match each model organism with the one biological process that it is best suited or most specifically useful for studying based on information provided in your textbook. Some of the biological processes may be used more than once, and some not at all. a. cell division b. development (multicellular) c. programmed cell death d. photosynthesis e. immunology 1. S. pombe 2. C. elegans 3. S. cerevisiae
4. D. rerio 5. D. melanogaster
57.Paramecium is a multicellular microorganism covered with hairlike cilia. a. True b. False
58.If you sequenced the genome of one type of differentiated cell in a plant or animal, it would include unique sequences that are not found in the genome of a second type of differentiated cell from the same plant or animal. a. True b. False
59.The presence of the plasma membrane can be inferred by the well-defined boundary of the cell. a. True b. False
60.The terms “prokaryote” and “bacterium” are synonyms. a. True b. False
61.Mitochondria are thought to have evolved from anaerobic bacteria. a. True b. False
62.With respect to cellular respiration, the only organelles used by animal cells are mitochondria, while plant cells use both mitochondria and chloroplasts. a. True b. False
63.The Golgi apparatus is made up of a series of membrane-enclosed compartments through which materials destined for secretion must pass. a. True b. False
64.Lysosomes are small organelles where fatty acid synthesis occurs. a. True b. False
65.Plant cells do not require a cytoskeleton because they have a cell wall that lends structure and support to the cell. a. True b. False
66.Thermal energy promotes random movement of proteins, vesicles, and small molecules in the cytosol. a. True b. False
67.Protozoans are single-celled eukaryotes with cell morphologies and behaviors that can be as complex as those of some multicellular organisms. a. True b. False
68.The first eukaryotic cells on Earth must have been aerobic; otherwise, they would not have been able to survive when the planet’s atmosphere became oxygenrich. a. True b. False
69.The variation in genome size among protozoans is larger than that observed
across all species of mammals, birds, and reptiles. a. True b. False
70.The human genome is roughly 30 times larger than the Arabidopsis genome but contains approximately the same number of protein-coding genes. a. True b. False
71.Generate an analogy to describe the cell as the simplest unit of life to somebody who has not studied biology. Be sure to incorporate the observable features of living organisms that distinguish them from inanimate objects.
72.Employ the principles of evolution discussed in this chapter to explain how the specific features and predatory behaviors of some primitive eukaryotes may have given them a selective advantage over others 1.5 billion years ago.
73.Cellular populations in bacterial colonies and the human body both start with single founder cells, yet these two collections of cells are vastly different. What is the primary reason for these differences?
74.Describe the benefits and limitations of utilizing electron microscopy to understand biological systems.
75.You fertilize egg cells from a healthy plant with pollen (which contains the male germ cells) that has been treated with DNA-damaging agents. You find that some of the offspring have defective chloroplasts, and that this characteristic can be passed on to future generations. This surprises you at first because you happen to know that the male germ cell in the pollen grain contributes no chloroplasts to the fertilized egg cell and thus to the offspring. What can you deduce from these results?
76.The protozoan Didinium feeds on other organisms by engulfing them. Describe the cellular characteristics necessary to feed this way and explain why this is not a mechanism by which bacteria can acquire energy. Are bacteria, in general, unable to feed on other cells in this way?
Consider the relative distribution of carbon among the groups of living organisms listed in the table below. Apply this information to answer the questions that follow. Carbon Store in Biosphere
Amount (gigatons)
Bacteria
70
Archaea
7
Plants
450
Animals
2
Total
529
77.Provide a rational explanation for how there can be 35 times more carbon stored in bacteria than in animals despite the huge differences in the overall sizes of these living organisms. Be sure your answer addresses both the relative numbers of bacteria and animals in the biosphere as well as their locations on the planet.
78.The planet’s biosphere is estimated to support roughly 550 gigatons of carbon. The groups of organisms in the table above leave a shortfall of about 21 gigatons. Suggest two additional groups of eukaryotes that you think may represent significant carbon stores in the biosphere and then compare their relative carbon distributions to those of plants and animals.
79.Describe the ultrastructural features of mitochondria, chloroplasts, and peroxisomes that allow biologists to identify and distinguish them in electron micrographs of eukaryotic cells.
80.Genes that have homologs in a variety of species have been discovered through
the analysis of genome sequences. In fact, it is common to find a family of homologous genes encoding proteins that are unmistakably similar in amino acid sequence in organisms as diverse as budding yeast, archaea, plants, and humans. Even more remarkably, many of these proteins can substitute functionally for their homologs in other organisms (i.e., if we delete a native gene and replace it with a homologous gene from another species, the protein will be produced and its function preserved). Use your understanding of evolution to explain how this is possible.
81.You have been following the recent presidential elections and have heard some candidates disparaging excessive and “unnecessary” federal government expenditures. One particular candidate asks: “Why are we spending millions of dollars studying fruit flies? How can that possibly help us find a cure for cancer?” Use your knowledge of model organisms to explain why studies in D. melanogaster (the fruit fly) are an excellent use of research funding.
82.Cellular processes are often regulated by unknown mechanisms. In many cases, biologists work backward in an attempt to understand a process in which they are interested. This was the case when Paul Nurse and Lee Hartwell were trying to understand how cell division is controlled in yeast. Describe the process by which they “broke” the system and then supplied the “missing parts” to get the cell cycle running again. What further evidence did they collect to show that human cells and yeast cells regulate the cell cycle using a similar mechanism?
83.Your friend has just returned from a deep-sea mission and claims to have found a new single-celled life-form. He believes this new life-form may not have descended from the common ancestor that all types of life on Earth share. You are convinced that he must be wrong, and you manage to extract DNA from the cells he has discovered. He says that the mere presence of DNA is not enough to prove the point: his cells might have adopted DNA as a useful molecule quite independently of all other known life-forms. What could you do to provide additional evidence to support your argument?
Evolutionary biologists have always used a broad range of modern organisms to infer the characteristics that ancestral organisms may have possessed. Genomic sequences are now available for an increasing number of species, and scientists studying evolutionary processes can take advantage of this enormous amount of
data to bring evolution into the arena of molecular studies. By aligning the sequences of homologous genes and looking for regions of similarity and where changes have occurred, it is possible to infer the sequence of the ancestral gene.
84.What term describes the changes in gene sequences that have occurred? How can we use what we know about this process to construct a time line showing when various sequence changes occurred and when they led to the modern sequences that we know today?
85.It is possible to express an ancestral gene sequence in modern organisms and subsequently compare the function of its product with that of the modern protein. Why might this approach give misleading conclusions?
The antibiotic streptomycin inhibits protein synthesis in bacteria. If this antibiotic is added to a culture of animal cells, protein synthesis in the cytosol continues normally. However, over time, the population of mitochondria in the cell becomes depleted. Specifically, scientists observe that the protein-synthesis machinery inside the mitochondria is inhibited.
86.Explain this observation based on what you know about the origins of the modern eukaryote.
87.What do you expect to observe if, in a new experiment, animal cells are treated with diphtheria toxin, a compound known to block cytosolic protein synthesis but that does not have any impact on bacterial growth?
Answer Key Chapter 01 1. Answer:
B
2. Answer:
A
3. Answer:
C
4. Answer:
C
5. Answer:
B
6. Answer:
A
7. Answer:
B
8. Answer:
B
9. Answer:
D
10.Answer:
D
11.Answer:
B
12.Answer:
C
13.Answer:
A
14.Answer:
D
15.Answer:
B
16.Answer:
A
17.Answer:
D
18.Answer:
B
19.Answer:
B
20.Answer:
C
21.Answer:
C
22.Answer:
A
23.Answer:
D
24.Answer:
B
25.Answer:
B
26.Answer:
D
27.Answer:
A
28.Answer:
C
29.Answer:
B
30.Answer:
D
31.Answer:
C
32.Answer:
D
33.Answer:
D
34.Answer:
B
35.Answer:
C
36.Answer:
D
37.Answer:
A
38.Answer:
B
39.Answer:
A
40.Answer:
B
41.Answer:
C
42.Answer:
B
43.Answer:
D
44.Answer:
C
45.Answer:
B
46.Answer:
1. D 2. F 3. C 4. A 5. B 6. E
47.Answer:
1. C 2. D 3. A 4. E 5. B 6. G 7. F
48.Answer:
1. G 2. D 3. G 4. B 5. E 6. D 7. D 8. D
49.Answer:
1. E 2. F
3. A 4. B 5. I 50.Answer:
1. C 2. A 3. C 4. B
51.Answer:
1. G 2. F 3. A 4. D 5. C
52.Answer:
1. B 2. B 3. A 4. A
53.Answer:
1. B 2. D 3. A 4. F 5. E 6. C
54.Answer:
1. A 2. B 3. A 4. B
5. A 55.Answer:
1. C 2. D 3. F 4. E
56.Answer:
1. A 2. C 3. A 4. B 5. B
57.Answer:
B
58.Answer:
B
59.Answer:
A
60.Answer:
B
61.Answer:
B
62.Answer:
B
63.Answer:
A
64.Answer:
B
65.Answer:
B
66.Answer:
A
67.Answer:
A
68.Answer:
B
69.Answer:
A
70.Answer:
A
71.Answer:
Cities, factories, and other types of human communities provide good models for analogical thinking about cells and organisms. Key elements that students should include are as follows: (1) organization—cities have organizational requirements for delivery of water, heat, and light, and for determining how things are moved and transported; (2) homeostasis— an example would include snow removal from city streets and thermostat-controlled temperatures inside buildings; homeostasis can also include waste removal via sewers and garbage trucks; (3) reproduction—blueprints and structural information for an entire city could be used to create a replica of any city; and (4) growth and development—cities grow in response to increases in population, and resources are expended to build new dwellings and increase the capacity to provide energy to them.
72.Answer:
Earth’s atmosphere became oxygen-rich roughly 1.5 billion years ago. If some primitive predatory eukaryotic cells were similar to modern-day protozoans, they may have been mobile and able to engulf other cells. These characteristics would have been advantageous in the face of a changing atmosphere, and the establishment of a symbiotic relationship with an engulfed aerobe would have been selected for in the eukaryotic cell populations.
73.Answer:
In humans and other complex multicellular species, multiple cell types arise from the single founder cell to perform specialized functions for the organism. In bacterial colonies, cells do communicate, but there is no observed development into differentiated cell types.
74.Answer:
Electron microscopy can provide biologists with sample magnification and resolution in the nanometer range. Samples must be fixed, thus preventing researchers from observing living cells.
75.Answer:
Your results show that not all the information required for making a chloroplast is encoded in the chloroplast’s own DNA; some, at least, must be encoded in the DNA carried in the nucleus.
The reasoning is as follows: Genetic information is carried only in DNA, so the defect in the chloroplasts must be due to a mutation in DNA. But all the chloroplasts in the offspring (and thus all the chloroplast DNA) must derive from those in the female egg cell, since chloroplasts only arise from other chloroplasts. Hence, all the chloroplasts contain undamaged DNA from the female parent’s chloroplasts. In all the cells of the offspring, however, half of the nuclear DNA will have come from the male germ-cell nucleus, which combined with the female egg nucleus at fertilization. Since this DNA has been treated with DNA-damaging agents, it must be the source of the heritable chloroplast defect. Thus, some of the information required for making a chloroplast is encoded by the nuclear DNA. 76.Answer:
For Didinium to engulf its prey, it needs to be larger than the cellular target, it needs to be mobile, and it needs to be able to change its shape. Movement and changing shape requires a flexible membrane and a dynamic cytoskeleton. By comparison, bacteria are small, have only a primitive cytoskeleton, and cannot easily change their shape because they are generally surrounded by a rigid cell wall. In general, bacteria are unable to feed on other cells using an engulfment mechanism.
77.Answer:
The data suggest that there are vastly more bacteria on the planet than there are animals. Considering the huge size differences between single-celled bacteria (prokaryotes) and multicellular animals (eukaryotes), bacteria must outnumber animals far more than the 35 times represented by their carbon distributions. Bacteria have been found in every conceivable habitat on the planet, including all those inhabited by animals, with most occupying the soil and oceans.
78.Answer:
Fungi and protists are not included in the table and should be predicted to account for significant proportions of the shortfall indicated. Neither group would come close to the 450 gigatons of carbon found within the plant biomass, but it is logical to predict that both would exceed the 2 gigatons of carbon found in animals, considering
the roles of fungi as decomposers and protists (algae) as primary producers. 79.Answer:
Electron micrographs of mitochondria and chloroplasts show that both of these organelles are surrounded by a double boundary membrane, whereas peroxisomes are surrounded by a single boundary membrane. In most cell types, peroxisomes are much smaller than mitochondria, and the latter are usually smaller than chloroplasts. Both mitochondria and chloroplasts also contain internal membranes, but their organization is very different. Those within mitochondria are continuous with the inner boundary membrane, whereas those within chloroplasts form an independent network of interconnected stacks or bundles.
80.Answer:
All living beings on Earth (and thus, all cells) are thought to be derived from a common ancestor. Solutions to many of the essential challenges that face a cell (such as the synthesis of proteins, lipids, and DNA) seem to have been achieved in this ancient common ancestor. The ancestral cell therefore possessed sets of proteins to carry out these essential functions. Many of the essential challenges facing modernday cells are the same as those facing the ancestral cell, and the ancient solutions are often still effective. Thus, it is common for organisms to use proteins and biochemical pathways inherited from their ancestors. Although these proteins usually show some species-specific diversification, they still retain the basic biochemical characteristics of the ancestral protein. For example, homologous proteins often retain their ability to interact with a specific protein target, even in cells of diverse species. Because the basic biochemical characteristics are retained, homologous proteins are often capable of functionally substituting for one another.
81.Answer:
Funding research on D. melanogaster is a worthwhile investment for several reasons: (1) working with insect animal models is relatively inexpensive; (2) fruit flies have proven useful historically in helping us understand eukaryotic chromosome behavior; and (3) many of the genes in Drosophila are highly similar in
sequence to the homologous human genes, and thus can be used to study human diseases like cancer. 82.Answer:
Nurse and Hartwell first treated yeast cells with a chemical mutagen. The mutated population of cells was then grown and observed. Cells that demonstrated defects in cell-cycle regulation (characterized by cell-cycle arrest, larger-thannormal cells, and smaller-than-normal cells) were then isolated. The use of a library of plasmids that each express a normal gene from yeast cells allowed the scientists to identify exactly which gene could be used to supply the missing parts and “rescue” the mutant, because when the normal gene is expressed again, the cells return to a normal cell cycle. After this big result, the scientists went on to show that the homologous gene from other organisms could also rescue the mutant phenotype. The most exciting result was obtained with the human version of the cdc2 gene, which demonstrated that there are common principles underlying cell-cycle regulation across a large range of eukaryotic organisms.
83.Answer:
I could use modern technology to discover the sequence of the DNA. If I am right, I would expect to find parts of this sequence that are unmistakably similar to corresponding sequences in other, familiar, living organisms; it would be highly improbable that such similar sequences would have evolved independently. I could, of course, also analyze other features of the chemistry of his cells; for example, do they contain proteins made of the same set of 20 amino acids? This could all be supporting evidence that this newly discovered species arose from the same common ancestral cells as all other life on Earth.
84.Answer:
Changes in gene sequence occur through mutation. Mutations accumulate over time, occurring independently and at different sites in each gene lineage. Homologous genes that diverged recently will differ only slightly; genes that diverged long ago will differ more. Knowing the average mutation rate, one can estimate the time that has elapsed since the different versions of the gene diverged. By seeing how
closely the various members of the family of homologous genes resemble one another, one can draw up a family tree, showing the sequence of lineage splits that lead from the ancestral gene to its many modern descendants. Suppose this family tree shows that family members A and B diverged from one another long ago, but that C diverged from B more recently. Suppose also that at a certain site in the gene, A and B have the same sequence but C is different. Then, it is likely that the sequence of A and B is ancestral, while that of C reflects a recent mutation that has occurred in the lineage of C alone. 85.Answer:
Although an inferred ancestral sequence can be reconstructed, and the protein expressed, one would be placing an inferred, ancient protein in the context of a modern cell. If there are important interacting partners for the modern protein, there is a chance they may not recognize the ancestral protein; therefore, any information about its function may be inaccurate.
86.Answer:
If the mitochondria originated from an ancient aerobic bacterium that was engulfed by an ancient eukaryote, as postulated, it is possible that an antibiotic that inhibits protein synthesis in bacteria could also block that process in mitochondria.
87.Answer:
We would expect that although cytosolic protein synthesis would stop, mitochondrial protein synthesis should still occur normally (at least for a little while). This result would lend further support to the idea that mitochondria are derived from a noneukaryotic organism. If this were not the case, these compounds would be expected to affect protein synthesis at both locations.
Name: ___________________________ Class: _________________ Date: __________
Chapter 02 1. Select the answer that best completes the following statement: Chemical reactions in living systems occur in an __________ environment, within a narrow range of temperatures. a. optimal b. organic c. extracellular d. aqueous
2. Which subatomic particles can vary between isotopes of the same element, without changing the observed chemical properties? a. electrons b. protons and neutrons c. neutrons d. neutrons and electrons
3. Which subatomic particles contribute to the atomic number for any given element? a. protons b. protons and neutrons c. neutrons d. protons and electrons
4. Which subatomic particles contribute to the atomic mass for any given element? a. protons b. protons and neutrons c. neutrons d. protons and electrons
5. You have a concentrated stock solution of 10 M NaOH and want to use it to produce a 150 mL solution of 3 M NaOH. What volume of water and stock solutions will you measure out to make this new solution? a. 135 mL of water; 15 mL of NaOH stock b. 115 mL of water; 35 mL of NaOH stock c. 100 mL of water; 50 mL of NaOH stock d. 105 mL of water; 45 mL of NaOH stock
6. The first task you are assigned in your summer laboratory job is to prepare a concentrated NaOH stock solution. The molecular mass of NaOH is 40. How many grams of solid NaOH will you need to weigh out to obtain a 500 mL solution that has a concentration of 10 M? a. 800 g b. 200 g c. 400 g d. 160 g
7. If the isotope 32S has 16 protons and 16 neutrons, how many protons, neutrons, and electrons will the isotope 35S have, respectively? a. 16; 20; 15 b. 16; 19; 15 c. 16; 19; 16 d. 16; 19; 17
8. Avogadro’s number was established as the total number of units (atoms or molecules) in a mole, and a mole of any substance is X grams of it, where X is equal to the substance’s mass. A standard unit, the mole, allows scientists to calculate concentrations of materials dissolved in solutions. Example: Sulfur has a mass of 32. Therefore, 32 g of sulfur = 1 mole of sulfur = 6 × 1023 sulfur atoms. How many moles and atoms, respectively, are there in 120 grams of sulfur? a. 3.75; 6 × 1023 b. 32; 6 × 1023
c. 1.75; 1.05 × 1024 d. 3.75; 2.25 × 1024
9. Figure 2-1 depicts the structure of carbon. Use the information in the diagram to choose the correct atomic number and atomic weight, respectively, for an atom of carbon.
Figure 2-1 a. 6; 12 b. 12; 12 c. 6; 18 d. 12; 6
10.Carbon 14 is an unstable isotope of carbon that decays very slowly. Compared to the common, stable carbon 12 isotope, carbon 14 has two additional a. electrons. b. neutrons. c. protons. d. ions.
11.There are 90 naturally occurring elements on Earth, __________ of which
compose 96% of the mass of living organisms. a. 4 b. 6 c. 7 d. 8
12.A covalent bond between two atoms is formed as a result of the a. sharing of electrons. b. loss of electrons from both atoms. c. loss of a proton from one atom. d. transfer of electrons from one atom to the other.
13.An ionic bond between two atoms is formed as a result of the a. sharing of electrons. b. loss of electrons from both atoms. c. loss of a proton from one atom. d. transfer of electrons from one atom to the other.
14.Table 2-1 indicates the number and arrangement of electrons in the first four atomic electron shells for selected elements. Based on the information in the chart and what you know about atomic structure, which elements are chemically inert?
Table 2-1 a. carbon; sulfur b. helium; neon c. sodium; potassium d. magnesium; calcium
15.Table 2-1 indicates the number and arrangement of electrons in the first four atomic electron shells for selected elements. Based on the information in the chart and what you know about atomic structure, which elements will form ions with a net charge of +1 in solution?
Table 2-1 a. carbon; sulfur b. helium; neon c. sodium; potassium d. magnesium; calcium
16.Table 2-1 indicates the number and arrangement of electrons in the first four atomic electron shells for selected elements. Based on the information in the chart and what you know about atomic structure, which elements will form ions with a net charge of +2 in solution?
Table 2-1 a. carbon; sulfur b. helium; neon c. sodium; potassium d. magnesium; calcium
17.Table 2-1 indicates the number and arrangement of electrons in the first four atomic electron shells for selected elements. Based on the information in the chart and what you know about atomic structure, which elements form stable but reactive diatomic gases?
Table 2-1 a. nitrogen; oxygen
b. helium; neon c. sodium; potassium d. magnesium; calcium
18.Which of the following factors do NOT influence the length of a covalent bond? a. the tendency of atoms to fill the outer electron shells b. the attractive forces between negatively charged electrons and positively charged nuclei c. the repulsive forces between the positively charged nuclei d. the minimization of repulsive forces between the two nuclei by the cloud of shared electrons
19.Double covalent bonds are both shorter and stronger than single covalent bonds, but they also limit the geometry of the molecule because they a. create a new arrangement of electron shells. b. change the reactivity of the bonded atoms. c. limit the rotation of the bonded atoms. d. prevent additional bonds from forming with the bonded atoms.
20.Polar covalent bonds form when the electrons in the bond are not shared equally between the two nuclei. Which of these molecules contains polar bonds? a. molecular oxygen b. methane c. propane d. water
21.Carbon atoms can form double bonds with other carbon atoms, nitrogen atoms, and oxygen atoms. Double bonds can have important consequences for biological molecules because they are __________ compared to single covalent bonds. a. long b. rigid with respect to rotation c. weak
d. unstable
22.Choose the combination of answers that best completes the following statement: When atoms are held together by __________, they are typically referred to as __________. a. hydrogen bonds; molecules b. ionic interactions; salts c. ionic interactions; molecules d. double bonds; nonpolar
23.Although covalent bonds are 10–100 times stronger than noncovalent interactions, many biological processes depend on the number and type of noncovalent interactions between molecules. Which of the noncovalent interactions below will contribute most to the strong and specific binding of two molecules, such as a pair of proteins? a. electrostatic attractions b. hydrogen bonds c. hydrophobic interactions d. van der Waals attractions
24.Which of the following expressions accurately describes the calculation of pH? a. pH = -log10[H+] b. pH = log10[H+] c. pH = -log2[H+] d. pH = -log10[OH-]
25.The pH of an aqueous solution is an indication of the concentration of available protons. However, you should not expect to find lone protons in solution; rather, the proton is added to a water molecule to form a(n) __________ ion. a. hydroxide b. ammonium c. chloride
d. hydronium
26.Larger molecules have hydrogen-bonding networks that contribute to specific, high-affinity binding. Smaller molecules such as urea can also form these networks. How many hydrogen bonds can urea (Figure 2-2) form if dissolved in water?
Figure 2-2 a. six b. five c. three d. four
27.Aromatic carbon compounds such as benzene are planar and very stable. Double-bond character extends around the entire ring, which is why it is often drawn as a hexagon with a circle inside. This characteristic is caused by electron a. resonance. b. pairing. c. partial charge. d. stacking.
28.Substances that release protons when they dissolve in water are acids. Which of the following household substances is acidic? a. coffee b. bleach c. hand soap
d. water
29.Cells contain buffers that help maintain a neutral pH. Which of the following statements is NOT relevant to how buffers work? a. Buffers are mixtures of weak acids and bases. b. Buffers can accept protons from acids. c. Buffers can donate protons to bases. d. Buffers catalyze oxidation-reduction reactions.
30.Which of the following monomer building blocks is necessary to assemble selectively permeable boundaries around and inside cells? a. sugars b. fatty acids c. amino acids d. nucleotides
31.__________ play an important role in organizing lipid molecules with long hydrocarbon tails into biological membranes. a. Hydrogen bonds b. Ionic bonds c. Hydrophobic forces d. Van der Waals attractions
32.There is incredible chemical diversity even in the simplest of cells. A typical bacterial cell contains more than 6000 different types of molecules. From the list below, select the class of molecules with the largest number of different types. a. nucleotides and precursors b. sugars and precursors c. amino acids and precursors d. fatty acids and precursors
33.Which of the following are examples of isomers?
a. glucose and galactose b. alanine and glycine c. adenine and guanine d. glycogen and cellulose
34.Oligosaccharides are short sugar polymers that can become covalently linked to proteins and lipids through condensation reactions. These modified proteins and lipids are called glycoproteins and glycolipids, respectively. Within a protein, which of the amino acids (shown in Figure 2-3) is the most probable target for this type of modification?
Figure 2-3 a. serine b. glycine c. phenylalanine d. methionine
35.Many types of cells have stores of lipids in their cytoplasm, usually seen as fat droplets. What is the lipid most commonly found in these droplets? a. cholesterol b. palmitic acid c. isoprene d. triacylglycerol
36.Choose the answer that best fits the following statement: Cholesterol is an essential component of biological membranes. Although it is much smaller than the typical phospholipids and glycolipids in the membrane, it is a(n) __________
molecule, having both hydrophilic and hydrophobic regions. a. polar b. oxygen-containing c. hydrophobic d. amphipathic
37.Most types of molecules in the cell have asymmetric (chiral) carbons. Consequently, there is the potential to have two different molecules that look much the same but are mirror images of each other and therefore not equivalent. These special types of isomers are called stereoisomers. Which of the four carbons circled in Figure 2-4 is the asymmetric carbon that determines whether the amino acid (threonine in this case) is a D or an L stereoisomer?
Figure 2-4 a. 1 b. 2 c. 3 d. 4
38.The amino acids glutamine and glutamic acid are shown in Figure 2-5. They differ only in the structure of part of their side chains (circled). At pH7, what type of interactions are possible for glutamic acid but not for glutamine?
Figure 2-5 a. ionic bonds b. hydrogen bonds c. van der Waals interactions d. covalent bonds
39.Cells require one particular monosaccharide as a starting material to synthesize nucleotide building blocks. Which of the monosaccharides below fills this important role? a. glucose b. fructose c. ribulose d. ribose
40.DNA and RNA are different types of nucleic acid polymer. Which of the following is true of DNA but NOT true of RNA? a. It contains uracil. b. It contains thymine. c. It is single-stranded. d. It has 5´-to-3´ directionality.
41.The variety and arrangement of chemical groups on monomer subunits contribute to the conformation, reactivity, and surface of the macromolecule into which they become incorporated. What type of chemical group is circled on the nucleotide shown in Figure 2-6?
Figure 2-6 a. pyrophosphate b. phosphoryl c. carbonyl d. carboxyl
42.Both DNA and RNA are synthesized by covalently linking a nucleoside triphosphate to the previous nucleotide, constantly adding to a growing chain. In the case of DNA, the new strand becomes part of a stable helix. The two strands are complementary in sequence and antiparallel in directionality. What is the principal force that holds these two strands together? a. ionic interactions b. hydrogen bonds c. covalent bonds d. van der Waals interactions
43.Each nucleotide in DNA and RNA has an aromatic base. What is the principal force that keeps the bases in a polymer from interacting with water? a. hydrophobic interactions b. hydrogen bonds c. covalent bonds d. van der Waals interactions
44.Because there are four different monomer building blocks that can be used to assemble RNA polymers, the number of possible sequence combinations that can be created for an RNA molecule made of 100 nucleotides is a. 1004. b. 4100. c. 4 × 100. d. 100/4.
45.There are 20100 different possible sequence combinations for a protein chain with 100 amino acids. In addition to the amino acid sequence of the protein, what other factors increase the potential for diversity in these macromolecules? a. free rotation around single bonds during synthesis b. noncovalent interactions sampled as protein folds c. the directionality of amino acids being added d. the planar nature of the peptide bond
46.Macromolecules in the cell can often interact transiently as a result of noncovalent interactions. These weak interactions also produce stable, highly specific interactions between molecules. Which of the factors below is the most significant in determining whether the interaction will be transient or stable? a. the size of each molecule b. the concentration of each molecule c. the rate of synthesis d. surface complementarity between molecules
47.Table 2-1 indicates the number and arrangement of electrons in the first four atomic electron shells for selected elements. Based on the information in the chart and what you know about atomic structure, which elements form stable but reactive diatomic gases?
Table 2-1 a. nitrogen; oxygen b. helium; neon c. sodium; potassium d. magnesium; calcium
48.Triacyclglycerols are examples of a. proteins. b. nucleic acids. c. monosaccharides. d. lipids.
49.One mole of sodium is the same as __________ of sodium. a. 46 grams b. 11 grams c. 6.022 x 1023 particles d. 35 grams
50.A nucleoside is different from a nucleotide in that a nucleoside has a. two phosphate groups.
b. a sugar and phosphate group. c. no phosphate group. d. only a base.
51.To break a glycosidic bond, a(n) __________ reaction will be performed. a. condensation b. hydrolysis c. oxidation d. isomerization
52.What is the relationship between 32sulfur and 35sulfur? a. isomers b. biomers c. monomers d. isotopes
53.What do polysaccharides, proteins, and nucleic acids have in common? a. They are polymers held together by glycosidic and peptide bonds. b. They are all made from monomer subunits linked by ionic bonds. c. They all contain a phosphate group and are linked by phosphodiester bonds. d. They are all made from monomer subunits linked by covalent bonds.
54.Oxygen, hydrogen, carbon, and nitrogen atoms are enriched in the cells and tissues of living organisms. The covalent bond geometries for these atoms influence the structure of larger biomolecules. Match the elements on the left with the bond geometries shown in Figure 2-7.
Figure 2-7 a. oxygen b. carbon c. nitrogen 1. Element 1 2. Element 2 3. Element 3 4. Element 4 5. Element 5 6. Element 6
55.Indicate whether the molecules below are inorganic (A) or organic (B). a. inorganic b. organic 1. glucose 2. ethanol 3. sodium chloride 4. water 5. cholesterol 6. adenosine 7. calcium 8. glycine 9. oxygen
10.iron 11.phospholipid
56.On the phospholipid molecule in Figure 2-8, label each numbered line with the correct term selected from the list below.
Figure 2-8 a. phosphate b. nonpolar head group c. glycerol d. polar head group e. saturated fatty acid f. acetic acid g. sugar h. hydrophobic region i. hydrophilic region j. unsaturated fatty acid 1. 1 2. 2 3. 3 4. 4 5. 5 6. 6 7. 7
57.Match each term related to the structure of nucleic acids (a–i) with one of the descriptions provided. a. base b. glycosidic bond c. nucleoside d. nucleotide e. phosphoanhydride bond f. phosphodiester bond g. ribose h. phosphodiester bond i. deoxyribose 1. the linkage between two nucleotides 2. the linkage between the 5′ sugar hydroxyl and a phosphate group 3. the nitrogen-containing aromatic ring 4. five-carbon sugar found in DNA 5. sugar unit linked to a base 6. linkage between the sugar and the base 7. linkages between phosphate groups 8. sugar linked to a base and a phosphate 9. five-carbon sugar found in RNA
58.For each of the following sentences, fill in the blanks with the best word or phrase selected from the list below. Not all words or phrases will be used; each word or phrase should be used only once. Whereas ionic bonds form a(n) _____1_____, covalent bonds between atoms form a(n) _____2_____. These covalent bonds have a characteristic bond _____3_____ and become stronger and more rigid when two electrons are shared in a(n) _____4_____. Equal sharing of electrons yields a(n) _____5_____ covalent bond. If one atom participating in the bond has a stronger affinity for the electron, this produces a partial negative charge on one atom and a partial positive charge on the other. These _____6_____ covalent bonds should not be confused with the weaker _____7_____ bonds that are critical for the threedimensional structure of biological molecules and for interactions between these molecules. a. polar b. molecule c. double bond
d. salt e. length f. noncovalent g. nonpolar h. ionic 1. 1 2. 2 3. 3 4. 4 5. 5 6. 6 7. 7
59.Table 2-1 indicates the number and arrangement of electrons in the first four atomic electron shells for selected elements. Use the information in the table to fill in the blanks for A–E. There may be more than one answer for each.
Table 2-1 a. Chlorine molecules b. Sodium and potassium c. Calcium and magnesium d. Helium and neon e. Nitrogen and oxygen 1. __________ are chemically inert. 2. __________ form ions with a net charge of +1 in solution. 3. __________ form stable but reactive diatomic gases. 4. __________ form ions with a net charge of −1 in solution.
5. __________ form ions with a net charge of +2 in solution.
60.For each of the following sentences, fill in the blanks with the best word or phrase selected from the list below. Not all words or phrases will be used; each word or phrase should be used only once. Proteins are _____1_____ built from amino acids, which each have an amino group and a _____2_____ group attached to the central _____3_____. There are 20 possible _____4_____ that differ in structure and are generally referred to as “R.” In solutions of neutral pH, amino acids are _____5_____, carrying both a positive and a negative charge. When a protein is made, amino acids are linked through _____6_____, which are formed by condensation reactions between the carboxyl end of the last amino acid and the _____7_____ end of the next amino acid to be added to the growing chain. a. amino b. side chains c. polypeptides d. carboxyl e. peptide bonds f. length g. α-carbon h. ionized i. R group 1. 1 2. 2 3. 3 4. 4 5. 5 6. 6 7. 7
61.A protein chain folds into its stable and unique three-dimensional structure, or conformation, by making many noncovalent bonds between different parts of the chain. Such noncovalent bonds are also critical for interactions with other proteins and cellular molecules. From the list provided, choose the class of amino acids that are most important for the interactions detailed below. a. acidic b. basic c. nonpolar
d. uncharged polar 1. forming ionic bonds with negatively charged DNA 2. forming hydrogen bonds to aid solubility in water 3. localizing an “integral membrane” protein that spans a lipid bilayer 4. tightly packing the hydrophobic interior core of a globular protein
62.Match each term related to particles of an atom (1–3) with one of the correct descriptions provided (a–e). Note not all descriptions will be used. a. neutral particles located in nucleus of an atom b. positively charged particles located in nucleus of an atom c. positively charged particles located in orbits around an atom d. neutral particles located in orbits of an atom e. negatively charged particles located in orbits around an atom 1. protons 2. neutrons 3. electrons
63.The chemical reactions in living systems are loosely regulated, allowing for a wide range of products and more rapid evolution. a. True b. False
64.Electron shells fill discrete regions around the nucleus of the atom and limit the number of electrons that can occupy a specific orbit. a. True b. False
65.Atoms with unfilled outer electron shells are especially stable and are therefore less reactive. a. True b. False
66.H, C, N, and O constitute 99% of the total number of atoms found in the human
body. a. True b. False
67.Copper, zinc, and manganese are among 11 nonessential trace elements that contribute less than 0.1% of all the atoms in the human body. a. True b. False
68.Protons are constantly moving between water molecules, which means there is an overall equilibrium between hydroxyl ions and hydronium ions in aqueous solutions. a. True b. False
69.A disaccharide consists of a sugar covalently linked to another molecule such as an amino acid or a nucleotide. a. True b. False
70.The hydroxyl groups on monosaccharides are reaction hot spots and can be replaced by other functional groups to produce derivatives of the original sugar. a. True b. False
71.Condensation reactions occur in the synthesis of all the macromolecules found in cells. a. True b. False
72.All proteins and RNAs pass through many unstable conformations as they are
folded, finally settling on one single, preferred conformation. a. True b. False
73.Amino acids possess a carboxylic acid group and an amino group. Based on this, we can conclude that amino acids are inorganic compounds. a. True b. False
74.The phosphoanhydride bonds in ATP are readily hydrolyzed. a. True b. False
75.If 0.5 mole of glucose weighs 90 grams, what is the mass of glucose?
76.How much glucose must you add to water to produce 1 liter of a 0.25 M solution of glucose?
77.How many molecules are in 1 mole of glucose?
78.You explain to a friend what you have learned about Avogadro’s number. Your friend thinks the number is so large that he doubts there is even a mole of living cells on Earth. You have recently heard that there are about 50 trillion (5 × 1013) human cells in each adult human body and that each human body carries more bacterial cells (the microbiome) than human cells, and the human population is approximately 7.6 billion (7.6 × 109). Armed with this information, you bet your friend $5 that there is more than a mole of cells on Earth. Write out the calculation that proves you are correct.
79.In which scientific unit is the strength of a chemical bond usually expressed?
80. If 0.5 kilocalories of energy are required to break 6 × 1023 bonds of a particular type, what is the strength of this bond?
81.The relative strengths of covalent bonds and van der Waals interactions remain the same when tested in a vacuum or in water. However, this is not true of hydrogen bonds or ionic bonds, whose bond strengths lower considerably in the presence of water. Explain these observations.
Refer to Figure 2-9 for the following questions.
Figure 2-9
82.How many carbon atoms does the molecule represented in Figure 2-9 have?
83.How many hydrogen atoms does the molecule represented in Figure 2-9 have?
84.What type of molecule is Figure 2-9?
85.Write out the sequence of amino acids in the following peptide, using the full names of the amino acids: Pro-Val-Thr-Gly-Lys-Cys-Glu.
86.Write out the sequence of amino acids in the following peptide, using the singleletter code of the amino acids: Pro-Val-Thr-Gly-Lys-Cys-Glu.
87.According to the conventional way of writing the sequence of a peptide or a protein, which is the C-terminal amino acid, and which is the N-terminal amino acid in the peptide Pro-Val-Thr-Gly-Lys-Cys-Glu?
88. The amino acid histidine is often found in enzymes. Depending on the pH of its environment, sometimes histidine is neutral and at other times it acquires a proton and becomes positively charged. Consider an enzyme with a histidine side chain that is known to have an important role in the function of the enzyme. It is not clear whether this histidine is required in its protonated or its unprotonated state. To answer this question, you measure enzyme activity over a range of pH, with the results shown in Figure 2-10. Which form of histidine is necessary for the active enzyme?
Figure 2-10
89.Silicon is an element that, like carbon, has four vacancies in its outer electron shell and therefore has the same bonding chemistry as carbon. Silicon is not, however, found to any significant degree in the molecules found in living systems. Does this difference arise because elemental carbon is more abundant than silicon? What other explanations are there for the preferential selection of carbon over silicon as the basis for the molecules of life?
90.Selenium (Se) is an element required in the human body in trace amounts. Selenium is obtained through the diet, and levels of selenium found in food
depend greatly on the soil where it is grown. Once ingested and absorbed as selenate, it can become incorporated into a small number of polypeptides. These selenoproteins are formed when selenium replaces an element that is found in 2 of the 20 “standard” amino acids. Using your knowledge of atomic structure, the periodic table in Figure 2-7, and the structure of amino acids found in Panel 2–5, deduce which two amino acids may be converted to “seleno” amino acids and used to make selenoproteins.
91.The cell can harvest energy from various processes in order to generate ATP molecules. These ATPs represent a form of stored energy that can be used later to drive other important processes. Explain how the cell can convert the chemical energy stored in ATP to generate mechanical energy—for example, changing the shape of a protein.
92.It is now a routine task to determine the exact order in which individual subunits have been linked in polynucleotides (DNA) and polypeptides (proteins). However, it remains difficult to determine the arrangement of monomers in a polysaccharide. Explain why this is the case.
93.As a protein is made, the polypeptide is in an extended conformation, with every amino acid exposed to the aqueous environment. Although both polar and charged side chains can mix readily with water, this is not the case for nonpolar side chains. Explain how hydrophobic interactions may play a role in the early stages of protein folding and how they have an influence on the final protein conformation.
94.You are trying to make a synthetic copy of a particular protein but accidentally join the amino acids in exactly the reverse order. One of your classmates says the two proteins must be identical and bets you $20 that your synthetic protein will have exactly the same biological activity as the original. After having read this chapter, you have no hesitation in staking your $20 that it will not. What particular feature of a polypeptide chain makes you sure your $20 is safe and that the project must be restarted?
Your lab director requests that you add new growth medium to the mammalian cell
cultures before heading home from the lab on a Friday night. Unfortunately, you need to make fresh medium because others have used all the premixed bottles of medium. One of the ingredients you know you need to add is a mix of the essential amino acids (those that cannot be made by the cells but are needed in proteins). On the shelf of dry chemicals, you find the amino acids you need, mix them into your medium (along with all the other necessary nutrients), and replace the old medium with your new medium. On Sunday, you go to the lab and find that the cells have not grown. You are sure you made the medium correctly, but on checking, you see that somebody wrote a note on the dry mixture of amino acids you used: “Note: this mixture contains only ᴅ-amino acids.”
95.What is the meaning of the note, and how does it explain the lack of cell growth in your culture?
96.Are there any organisms that could grow using this mixture? Justify your answer.
Eukaryotic cells have their DNA molecules inside their nuclei. However, to package all the DNA into such a small volume requires the cell to use specialized proteins called histones. Histones have amino acid sequences enriched for lysines and arginines.
97.What problem might a cell face in trying to package DNA into a small volume without histones, and how do these special packaging proteins alleviate the problem?
98.Lysine side chains are substrates for enzymes called acetylases. A diagram of an acetylated lysine side chain is shown in Figure 2-11. How do you think the acetylation of lysines in histone proteins will affect the ability of a histone to perform its role?
Figure 2-11
99. Complete the following reaction: CH3COOH + H2O ↔ __________
100. Will the reaction in (C) occur more readily (be driven to the right) if the pH of the solution is high?
101.
Name three similarities and differences between DNA and RNA.
102. Your friend asks you about the feasibility of creating a new compound “neonic chloride,” which should be made from neon and chlorine. Please explain your answer, using Table 2-1 as a reference
Table 2-1
Answer Key Chapter 02 1. Answer:
D
2. Answer:
C
3. Answer:
A
4. Answer:
B
5. Answer:
D
6. Answer:
B
7. Answer:
C
8. Answer:
D
9. Answer:
A
10.Answer:
B
11.Answer:
A
12.Answer:
A
13.Answer:
D
14.Answer:
B
15.Answer:
C
16.Answer:
D
17.Answer:
A
18.Answer:
A
19.Answer:
C
20.Answer:
D
21.Answer:
B
22.Answer:
B
23.Answer:
A
24.Answer:
A
25.Answer:
D
26.Answer:
A
27.Answer:
A
28.Answer:
A
29.Answer:
D
30.Answer:
B
31.Answer:
C
32.Answer:
B
33.Answer:
A
34.Answer:
A
35.Answer:
D
36.Answer:
D
37.Answer:
C
38.Answer:
A
39.Answer:
D
40.Answer:
C
41.Answer:
B
42.Answer:
B
43.Answer:
A
44.Answer:
B
45.Answer:
B
46.Answer:
D
47.Answer:
A
48.Answer:
D
49.Answer:
C
50.Answer:
C
51.Answer:
B
52.Answer:
D
53.Answer:
D
54.Answer:
1. B 2. C 3. B 4. A 5. C 6. A
55.Answer:
1. B 2. B 3. A 4. A 5. B 6. B 7. A
8. B 9. A 10. A 11. B 56.Answer:
1. D 2. A 3. C 4. J 5. I 6. H 7. E
57.Answer:
1. H 2. F 3. A 4. I 5. C 6. B 7. E 8. D 9. G
58.Answer:
1. D 2. B 3. E 4. C 5. G 6. A
7. F 59.Answer:
1. D 2. B 3. E 4. A 5. C
60.Answer:
1. C 2. D 3. G 4. B 5. H 6. E 7. A
61.Answer:
1. B 2. D 3. C 4. C
62.Answer:
1. B 2. A 3. E
63.Answer:
B
64.Answer:
A
65.Answer:
B
66.Answer:
A
67.Answer:
B
68.Answer:
A
69.Answer:
B
70.Answer:
A
71.Answer:
A
72.Answer:
A
73.Answer:
B
74.Answer:
A
75.Answer:
180 daltons. A mole of a substance has a mass equivalent to its molecular mass expressed in grams.
76.Answer:
45 g/L
77.Answer:
6 × 1023 molecules
78.Answer:
Avogadro’s number, or 6 × 1023, is the number of atoms or molecules in a mole. If I multiply the number of people on Earth by the number of cells in the human body, then double it to account for the bacteria, I will calculate: (7 × 109) × (1 × 1014) = 7 × 1023. Thus, even when only considering the human population and the associated microbial populations, I can estimate more than a mole of living cells on Earth. I win $5.
79.Answer:
kilocalories per mole (or kilojoules per mole)
80.Answer:
0.5 kcal/mole
81.Answer:
We estimate bond strengths by measuring the amount of energy needed to break them. As explained in Panel 2–7 in the text (pp. 78–79), in an aqueous solution, water can form hydrogen bonds with any polar molecules that are capable of forming hydrogen bonds with each other. This formation of bonds with water takes away from the net energy that would be gained from the molecules forming hydrogen bonds with each other, as they would in a vacuum. Similarly, water forms favorable electrostatic interactions with ions, thereby greatly weakening the ionic bonds that form between positive and negative ions in a vacuum (see Panel 2–7). Thus, for example, solid table
salt (NaCl) readily dissociates in water, producing separate Na+ and Cl− ions as it dissolves. In contrast, covalent bonds and van der Waals attractions have an intrinsic bond strength that is independent of the aqueous environment, because changes in water molecule associations are not involved in the formation of these two types of bonds. 82.Answer:
20 carbon atoms
83.Answer:
31 hydrogen atoms
84.Answer:
a fatty acid
85.Answer:
proline-valine-threonine-glycine-lysine-cysteine-glutamic acid (or glutamate)
86.Answer:
PVTGKCE
87.Answer:
The C-terminal is glutamic acid (or glutamate); the Nterminal is proline.
88.Answer:
Assuming that the change in enzyme activity is due to the change in the protonation state of histidine, the enzyme must require histidine in the protonated, charged state. The enzyme is active only at low, acidic pH, where the proton (or hydronium ion) concentration is high; thus, the loss of a proton from histidine will be disfavored so that histidine is likely to be protonated.
89.Answer:
According to Figure 2-4 in your textbook, silicon is more abundant in Earth’s crust than carbon, so this is not likely to be the reason that carbon was used preferentially. Carbon might have been the element of choice in living systems because it is lighter than silicon and forms shorter covalent bonds with other elements. Shorter bonds are typically stronger and more stable.
90.Answer:
Sulfur is the only element found exclusively in 2 of the 20 amino acids. This element is located directly above selenium in the periodic table, indicating that these elements have the same number of electrons in their outer shells, and both prefer to form bonds with other atoms to fill their outer orbital. If selenium instead of sulfur is incorporated into cysteine or methionine, the altered “seleno” amino acids will be produced (selenocysteine and selenomethionine). We can expect that this substitution will alter the nature of the proteins
in which these amino acids are incorporated because selenium is a larger atom than sulfur. 91.Answer:
The terminal phosphate group is typically hydrolyzed, and the energy released from this chemical bond is often “reinvested” to generate a new bond that links the phosphate group to a protein. This addition of a phosphate group can cause a change in the protein’s conformation. This conformational change is usually associated with change in function or transient interactions with other macromolecules, generating a domino effect within the cell.
92.Answer:
Nucleotides and amino acids have an intrinsic directionality, and the mechanism by which monomers are added into a growing polymer is always the same. This yields a linear polymer with the same directionality as the monomers. Polysaccharides are produced by linking monosaccharides. The monosaccharides can be either added directly or modified to produce various derivatives before addition. Beyond this, there are multiple sites on each monosaccharide where addition can occur, producing highly complex, branched polymers.
93.Answer:
One reason that nonpolar groups are excluded from an aqueous environment is that a hydrophobic surface would organize water into a highly structured network of hydrogen bonds, which is energetically unfavorable. Thus, you would expect that nonpolar amino acids would group together early, forming “hydrophobic pockets,” while the polar and charged side chains remain at the interface of the surrounding solution. In the final, folded protein, most of the nonpolar amino acids will remain buried inside the protein. This fold is more stable because nonpolar atoms are prevented from contact with water and remain in contact with each other.
94.Answer:
As a peptide bond has a distinct chemical polarity, a polypeptide chain also has a distinct polarity. The reversed protein chain cannot make the same noncovalent interactions during folding and thus will not adopt the same three-dimensional structure as the original protein. The activities of these two proteins will definitely be different, because the activity of a protein depends on its three-dimensional structure. It is unlikely that the reverse chain will fold into any well-defined, and hence functionally useful, structure at all, because it has not passed the stringent selective pressures imposed
during evolution. 95.Answer:
The note indicates that the mixture contains only one of the two possible stereoisomers (ʟ or ᴅ). Because mammalian cells use only the ʟ stereoisomer, the ᴅamino acid mixture could not be used and therefore it is as though no amino acids were added at all.
96.Answer:
No, not unless ʟ-amino acids were also mixed in. Certain types of bacteria use ᴅ-amino acids to produce their cell walls, but they would still require ʟ-amino acids for the rest of the proteins they make.
97.Answer:
DNA is a nucleic acid polymer in which each monomer has a negatively charged phosphate group. The negative charges will naturally repel each other, so to wrap the high density of negative charges into a small space, positively charged molecules must be present. Histones accomplish this because they are rich in lysines and arginines, which are positively charged in solution at pH7.
98.Answer:
A histone with acetylated lysine residues will not be as good at packaging the DNA. The addition of the acetyl group to the terminal amino on the lysine side chain lowers the histone’s net positive charge, which makes it less effective at buffering the negative charges on the DNA backbone.
99.Answer:
CH3COO− + H3O+
100.
Answer: Yes. If the pH is high, then the concentration of hydronium ions will be low. Therefore, the rightward reaction, which produces hydronium ions, will be favored.
101.
Answer: Differences 1. DNA contains thymine, while RNA contains uracil. 2. DNA is a double stranded, long-term carrier of genetic information, while RNA is usually single-stranded and a transient carrier of genetic information. 3. DNA contains deoxyribose sugar, while RNA contains ribose sugar. Similarities 1. They are both polymers, made from monomers of nucleotides. 2. They both have four bases and have rules for base pairing. 3. They store and transmit hereditary information.
102.
Answer: It is not a feasible experiment because the outermost shell of neon is entirely filled with electrons. It is stable and it is chemically unreactive.
Name: ___________________________ Class: _________________ Date: __________
Chapter 03 1. Chemical reactions carried out by living systems depend on the ability of some organisms to capture and use atoms from nonliving sources in the environment. The specific subset of these reactions that break down nutrients in food can be described as a. metabolic. b. catabolic. c. anabolic. d. biosynthetic.
2. When there is an excess of nutrients available in the human body, insulin is released to stimulate the synthesis of glycogen from glucose. Glycogen synthesis is an example of a(n) __________ process, a general process in which larger molecules are made from smaller molecules. a. metabolic b. catabolic c. anabolic d. oxidative reductive
3. The second law of thermodynamics states that the disorder in any system is always increasing. In simple terms, you can think about dropping NaCl crystals into a glass of water. The solvation and diffusion of ions is favored because there is an increase in a. pH. b. entropy. c. ions. d. stored energy.
4. The energy used by the cell to generate specific biological molecules and highly ordered structures is stored in the form of a. Brownian motion.