13. A hierarchical organization, metabolism, growth and development, responsiveness, regulation, and reproduction are characteristics common to all living organisms. All living things are arranged in a hierarchical manner with increasing levels of complexity from molecules to cells. They are capable of metabolism, growth and development, and responsiveness to stimuli. They are also able to regulate their internal environment in order to maintain homeostasis, ultimately surviving long enough to reproduce. 14. The human body consists of eleven organ systems. They are the integumentary, skeletal, muscular, nervous, endocrine, cardiovascular, lymphatic, respiratory, urinary, digestive, and reproductive systems. 15. A body in anatomical position is standing upright with the feet flat on the floor. The upper limbs are at the side of the body with palms facing anteriorly. The head is level and the eyes are looking forward. The anatomic position is the point of common reference used by anatomists and physiologists for accuracy and clarity. It provides an initial point of reference, from which all anatomic parts are described. 16. The forearm is the antebrachial region, the wrist is the carpal region, the chest is the thoracic region, the armpit is the axillary region, the thigh is the femoral region, and the entire foot is the pes. 17. The cranial cavity and vertebral canal are located within the posterior aspect of the body. The cranial cavity houses the brain and the vertebral canal contains the spinal cord. 18. The serous membranes are found lining the compartments of the ventral cavity of the body. They consist of a parietal layer lining the inside of the body wall and a visceral layer covering internal organs. In between the two membranes is a potential space, the serous cavity, which contains serous fluid. 19. A homeostatic system consists of a receptor that detects an internal or external stimulus, a control system that integrates the input from the receptor, and an effector such as a muscle or a gland that causes changes in response to the stimulus. 20. Negative feedback systems involve responses that are in opposition to the stimulus, thereby maintaining the environment near the set point or normal level. Conversely, positive feedback systems entail a series of responses, each increasing in intensity until a climax event is reached, at which point the system will return to homeostasis.
Answers to “Can You Apply What You’ve Learned?” 1. B Feedback: The pain is coming from a region below the umbilicus, hence it is in the lower portion of the abdomen and it is located on the right side. It is therefore in the right lower quadrant. 2. D Feedback: The right iliac region is located just medial to the pelvic bones. 3. B Feedback: X-rays are not absorbed by soft tissue such as the appendix. They are usually used to visualize dense structures. 4. B Feedback: Sweat glands release sweat at the surface of the skin. 5. B Feedback: Serotonin is a neurotransmitter responsible for regulating both pathways associated with depression in the brain and gastric motility in the stomach. Drugs such as SSRIs are used to treat depression in individuals with low levels of serotonin in the brain by inhibiting its reuptake by neurons. Because the SSRI drugs cannot specifically target the brain, they also have an effect within the digestive system, causing nausea and diarrhea.
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Answers to “Can You Synthesize What You’ve Learned?” 1. Lynn has broken the bones within her forearm, the radius and ulna. She has an abrasion on her chin as well as bruising on her buttocks and thigh. 2. The epinephrine counteracted the effect of the bee sting, acting in opposition to the stimulus; it was therefore an example of negative feedback. 3. X-rays and CT scans are optimal for visualizing dense tissues such as tumors. An MRI or ultrasound would be better suited for examining soft tissues.
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Chapter 2 Answers to “What Did You Learn?” 1.The mass of an atom is determined by the combined number of protons and neutrons within its nucleus. The charge of an atom is determined by the number of positively charged protons and negatively charged electrons. 2.The nucleus of a chlorine atom consists of 17 protons and 18 neutrons. The electrons are arranged into three separate shells; the first shell closest to the nucleus contains two electrons, the second shell contains eight electrons, and the third outer shell contains seven electrons for a total of 17 electrons.
17P 18N
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3. Isotopes are atoms of the same element. They only differ in their number of neutrons, thus they differ in their atomic mass. A radioisotope is unstable because of extra neutrons. Stability can ultimately be reached through the loss of nuclear components in the form of high-energy radiation (e.g., alpha particles, beta particles). Thus, the radioisotope will decay as radiation is released. 4. The octet rule is the tendency for atoms to lose, gain or share electrons to obtain a complete outer shell and thus become chemically stable. 5. Common cations (positively charged ions) of the human body include: sodium ions (Na+), potassium ions (K+), calcium ions (Ca2+), magnesium ions (Mg2+), and hydrogen ions (H+). Common anions (negatively charged ions) include: chloride ions (Cl–), bicarbonate ions (HCO3−), and phosphate ions (PO43–). 6. Sodium (atomic number 11), potassium (atomic number 19), calcium (atomic number 20), magnesium (atomic number 12), hydrogen (atomic number 1), and chlorine (atomic number 17) should be highlighted. 7. In order to satisfy the octet rule, atoms may either lose or gain electrons to become chemically stable (have a complete outer shell of electrons). However, a charge is developed because the number of positively charged protons is no longer equal to the number of negatively charged electrons. For example, atoms with only one electron in their outer shell may give up the electron, resulting in a positive cation, now with a full outer shell. Conversely, atoms with seven electrons in their outer shell may accept an electron from another atom, becoming a negative anion, but now with a full outer shell. 8. Ionic bonds are formed due to an attraction between ions with different charges. Therefore, an ionic bond cannot be formed between two cations; nor can it be formed between two anions. 9. The structural formula exhibits the type and number of atoms in a molecule, and their arrangement within the molecule. In comparison, the molecular formula provides information only for the type and number of atoms in a molecule (but not how the atoms are arranged within the molecule). 10. Isomers are molecules composed of the same type and number of elements, but are arranged differently (i.e., they have the same molecular formula, but a different structural formula). 11. A covalent bond is formed when atoms share electrons in their outer orbitals in order to satisfy the octet rule. 12. Nitrogen is more electronegative that hydrogen, thus it is designated with a partial negative charge, whereas hydrogen is less electronegative than nitrogen and is designated with a partial positive charge.
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13. A covalent bond between atoms of the same element (with both atoms equally electronegative) will result in electrons being shared equally between the two atoms. Thus, the resulting bond is a nonpolar bond. A covalent bond formed between two different atoms (with one atom more electronegative than the other) will result in electrons being shared unequally between the two atoms. Thus, the resulting bond is a polar bond. The more electronegative atom will have a slightly negative charge and the less electronegative atom will have a slightly positive charge. Note: Because carbon and hydrogen atoms are nearly equal in terms of electronegativity, atoms of these two different elements essentially share electrons equally and form a nonpolar covalent bond between them. 14. Both molecular oxygen (O2) and carbon dioxide (CO2) are nonpolar molecules. (This is significant for understanding how these respiratory gases are transported in the blood, a topic that is covered in chapter 23.) 15. A hydrogen bond is a weak attraction between a partially positive hydrogen atom within a polar molecule and a partially negative atom within a polar molecule (usually oxygen, but sometimes nitrogen). 16. Hydrogen bonds are the intermolecular bonds that are significant in determining the properties of water. 17. Surfactant is required to decrease surface tension (the cohesive attraction between water molecules) in the alveoli of the lungs. Body temperature is regulated through sweating because of water’s high heat of vaporization. Sweating is less effective on a humid day because of the increased water in the environment that impedes additional water evaporating from the skin. 18. Nonelectrolyte molecules such as glucose dissolve but do not dissociate in water. Electrolytes such as sodium chloride (NaCl) both dissolve and disassociate into constituent ions in water, forming a solution capable of conducting electricity. 19. In an aqueous environment, amphipathic molecules such as phospholipids will orient themselves so that their hydrophobic domains face each other while the hydrophilic portions are exposed to water. This is the basis for the arrangement of phospholipids within a bilayer and a micelle. 20. Each water molecule can disassociate into one positively charged hydrogen ion and one negatively charged hydroxyl ion. It is considered neutral since it has an equal distribution of positive and negative charges. 21. An acid dissociates in water and releases hydrogen ions. 22. pH is a measure of the relative amounts of H+ in a solution. The relationship between [H+] and pH is inverse. As [H+] increases, pH decreases, whereas as [H+] decreases, pH increases. 23. A buffer helps prevent pH changes if either excess acid or base is added. It acts either to accept H+ from excess acid or donate H+ to neutralize excess base. (Buffers act as H+ sponges, absorbing H+ if acid is added and releasing H+ if base is added.) 24. Blood would be characterized as a suspension because blood cells settle to the bottom of a tube when left standing. 25. Blood is also considered a colloid because it contains a mixture of proteins within the liquid portion of the blood, and it is a solution because it contains salts, glucose and other dissolved nonprotein substances in the plasma. 26. The concentration of a solution may be expressed as (1) mass of solute per volume of solution [mass/volume], (2) grams of solute per 100 milliliters (mL) of solution [mass/volume percent], (3) moles of solute per liter of solution [molarity], and (4) moles of solute per kilogram of solvent [molality]. 27. Biological molecules typically contain carbon (C), hydrogen (H), and oxygen (O) and in some cases may also contain nitrogen (N), phosphorus (P), and sulfur (S). Hydrogen is the element that both (a) forms a common ion and (b) is a common element in biomolecules. 28. Carboxylic acids and phosphates are capable of acting as acids.
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29. A polymer is composed of repeating monomer subunits. Proteins are composed of amino acid monomers, carbohydrates contain sugar monomers, and nucleic acids have nucleotide monomers. 30. Lipids are fatty, water-insoluble, hydrophobic molecules and do not typically dissolve in water. 31. Phospholipids are amphipathic molecules that form chemical barriers of cell membranes. They contain both a hydrophilic head group (that dissolves in water) and a pair of hydrophobic fatty acid tails (that do not dissolve in water), making them ideally suited for forming cellular membranes. 32. Glycogen is composed of repeating glucose monomers or subunits and is stored by animals within the liver and skeletal muscle cells. 33. Fructose, galactose, and glucose are monosaccharides. Sucrose, maltose, and lactose are disaccharides. Glycogen and starch are polysaccharides. 34. Nucleic acids store and transfer genetic information within cells. They ultimately determine the types of proteins synthesized within cells. 35. RNA molecules contain a ribose sugar in their nucleotides rather than the deoxyribose sugar that is within the nucleotides of DNA. The nucleotides of both RNA and DNA may contain the nitrogenous bases of adenine, guanine, and cytosine. The base uracil is present within nucleotides of RNA. In comparison, the base thymine is present in the nucleotides composing DNA. RNA is a single strand, whereas DNA is a double strand (double helix). 36. Amino acids are the monomers of a protein and they are covalently linked by peptide bonds. 37. A dipeptide consists of 2 amino acids, an oligopeptide contains 3 to 20 amino acids, a polypeptide contains 21 to 199 amino acids, and a protein consists of 200 or more amino acids. The term protein is generally used to refer to oligopeptide, polypeptide and protein. 38. The R group of leucine is a nonpolar hydrocarbon, making it a nonpolar amino acid. 39. The tertiary structure refers to the three-dimensional shape exhibited by one completed polypeptide chain. The quaternary structure refers to the three-dimensional shape of two or more polypeptide chains that form the functional protein. 40. Denaturing a protein changes its conformation and affects its activity. Exposure of a protein to higher than normal concentration of hydrogen ions (a decrease in pH) results in the positively charged H+ binding with negatively charged structures that were participating in electrostatic interactions that were holding the protein in its final shape. The loss of these electrostatic interactions between the amino acids that compose the protein results in its unfolding (or denaturation).
Answers to “Do You Know the Basics?” 1. C Feedback: Isotopes are atoms of the same element that have the same number of protons and electrons, but differ in the number of neutrons. 2. A Feedback: Lipids are hydrophobic molecules and are not soluble (do not dissolve) in water. 3. C Feedback: Water has a high specific heat, allowing it to absorb and release energy without changing temperature. In addition, the high heat of vaporization for water allows it to dissipate a large amount of energy during evaporative cooling of the skin.
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4. D Feedback: A pH less than 7.0 is acidic and a pH greater than 7.0 is basic. 5. D Feedback: The formed elements of blood act as a suspension. Dissolved proteins in the plasma act as a colloid. The numerous dissolved solutes also make blood a solution. 6. A Feedback: Triglycerides are not considered polymers because they are not composed of repeating monomer subunits. 7. C Feedback: Glucose is stored in animal tissues as glycogen. 8. B Feedback: Although phosphates which contain phosphorus are common ions in the body, phosphorus itself is not a common ion. 9. B Feedback: A hydrogen bond is an intermolecular attraction between a slightly positive hydrogen atom within a polar molecule and a slightly negative atom (e.g., oxygen, nitrogen) in a polar molecule. 10. B Feedback: Denaturing a protein changes its conformation. Excessive denaturation can permanently affect protein structure and possibly its function as well. 11. Common cations of the human body include sodium ions (Na+), potassium ions (K+), calcium ions (Ca2+), magnesium ions (Mg2+), and hydrogen ions (H+). Common anions include chloride ions (Cl-), bicarbonate ions (HCO3-), and phosphate ions (PO43-). 12. Polar bonds have varying degrees of unequal electron sharing between two different atoms, except for C-H, an oxygen atom bonded to a hydrogen atom. Oxygen, the more electronegative of the atoms, will have a stronger pull on the electrons and will thus have a slightly more negative charge around it, while the hydrogen atom will be relatively more positive (or less negative). A polar molecule is a molecule that contains a prevalence of polar bonds between the atoms that compose it. For example, water is a polar molecule composed of two polar covalent bonds between the oxygen atom and each hydrogen atom. 13.
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14. Polar molecules (e.g., glucose) will dissolve in water because hydrogen bonds are formed between the water and the polar molecules. The polar molecule does not dissociate, remaining intact as in this example of a glucose molecule. In comparison, ionic compounds both dissolve and dissociate. Ionic compounds such as sodium chloride (NaCl) will disassociate in water because the polar water molecules will disrupt the electrostatic interactions between sodium and chloride ions, thereby separating them. 15. An acid contributes hydrogen ions to a solution, making it more acidic (having a lower pH). A base binds hydrogen ions from a solution, making it more basic (having a higher pH). pH is the measure of hydrogen ions in a solution. A buffer is capable of either absorbing or releasing hydrogen ions, thereby helping to prevent pH changes when acids or bases are added. 16. The concentration of a solution may be expressed as either the ratio of the mass of solute compared to the volume of the solution (mass/volume), as the percent of mass of solute in 100 milliliters of solution (mass/volume %), as the number of moles of solute per liter of solution (molarity), or the number of moles of solute per kilogram of solvent (molality). 17. Proteins are composed of amino acids (repeating units); carbohydrates are composed of simple sugars (repeating units); nucleic acids are composed of nucleotides (repeating units); but lipids are not composed of repeating units. There are four primary types of lipids: triglycerides (composed of glycerol and fatty acids); phospholipids (composed of glycerol, two fatty acids, a phosphate, and various organic groups); steroids (cholesterol, steroid hormones, and bile salts—composed predominantly of hydrocarbons that differ in the side chains extending from the rings); and eicosanoids (prostaglandins, thromboxanes, and leukotrienes—composed of modified 20-carbon fatty acids synthesized from arachidonic acid). 18. Nucleotides (composed of a sugar, phosphate, and a nitrogenous) that compose DNA and RNA contain nitrogen that forms a nitrogenous waste called uric acid. Amino acids contain an amine functional group, —NH2, that is converted to a nitrogenous waste called urea. Both uric acid and urea must be effectively eliminated by the kidney for an individual to remain healthy. 19. In an aqueous environment, amphipathic molecules such as phospholipids will orient themselves so that their hydrophobic domains face each other while the hydrophilic domains are exposed to water. This is the basis behind the arrangement of phospholipids within a phospholipid bilayer of the plasma membrane of a cell. 20. A protein’s function is dependent upon the retention of its normal 3-dimensional shape. Denaturation is a change in the conformation of a protein that changes/affects its activity. Exposure of a protein to either an increase in temperature or a pH outside of its normal environment can denature the protein by disrupting electrostatic interactions such as ionic bonds within the molecule. An increase in temperature can weaken the intramolecular attractions between the amino acids in the primary structure of the protein strand, causing the protein to unfold or denature such that it can no longer function normally. Changes in H+ concentration that are associated with changes in pH interfere with the electrostatic interactions within the protein that hold it in its 3-dimensional shape. Exposure of a protein to higher than normal concentration of hydrogen ions (a decrease in pH) results in the positively charged H+ binding with negatively charged structures that were participating in electrostatic interactions that were holding the protein in its final shape. Exposure of a protein to lower than normal concentration of hydrogen ions (an increase in pH) results in the positively charged H+ that were participating in electrostatic interactions and holding the protein in its final shape being removed. The loss of these electrostatic interactions between the amino acids that compose the protein results in its unfolding (or denaturation).
Answers to “Can You Apply What You’ve Learned?” 1. C Feedback: Surface tension is high within the air sacs in the lungs of premature infants that are not producing sufficient surfactant. Surfactant is a detergent-like substance that prevents hydrostatic interactions between water molecules, thereby preventing the lungs from collapsing and the alveolar walls from sticking together. Premature babies often lack the ability to produce surfactant and are at risk for respiratory problems.
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2. B Feedback: Electrolytes such as sodium ions, potassium ions, and chloride ions are capable of conducting electricity. Nonelectrolytic molecules such as glucose are not able to conduct electricity. 3. B Feedback: Isotopes are atoms of the same element that differ in their number of neutrons. In a radioisotope the extra neutrons will decay and be released as radiation, which may be measured or visualized during a diagnostic test. 4. D Feedback: Calcium (Ca2+) ions are an important structural component of bone tissue. 5. C Feedback: Proteins consist of covalently bonded amino acids held together by peptide bonds. If insulin is administered orally, the peptide bonds are broken by enzymes of the digestive system (to form individual amino acids).
Answers to “Can You Synthesize What You’ve Learned?” 1. High-energy radiation can cause mutations within DNA. 2. The number of hydrogen ions in the blood increases, resulting in a lower pH (a condition called acidosis). The increasing number of hydrogen ions may interfere with the hydrostatic interactions holding proteins together, thus denaturing the proteins. 3. The drug would regulate the levels of the monosaccharide glucose within the blood.
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Chapter 3 Answers to “What Did You Learn?” 1. Kinetic energy is the energy of motion. Movement of sodium ions along a concentration gradient or the movement of electrons from a higher to lower energy state are both examples of kinetic energy. 2. The movement of muscle is an example of mechanical energy, a form of kinetic energy that involves the movement of an object due to an applied force. 3. Even though energy can neither be created nor destroyed, it can be transformed or converted from one form to another. Such transformations are not completely efficient, always resulting in the release of some of the energy as heat, which is not available to do work. 4. Reactants are the substrates or substances that are present prior to a chemical reaction. The reactants are converted to products during the reaction. 5. Formation of a complex molecule from simpler chemical structures would be classified as: (a) a synthesis reaction, (b) an endergonic reaction, and (c) a form of anabolism. 6. ATP is the molecule that produced by exergonic reactions and used to couple exergonic reactions to endergonic reactions (chemical reactions that require an input of energy) and other energy-requiring processes within the cell. 7. When equilibrium is disturbed in a reversible reaction, the system will adjust and the reaction is driven toward either the reactants or the products until equilibrium is reestablished. For example, an increase in substrates drives the chemical reaction to the right (making more product) until a new equilibrium is reached. 8. Initially, the effect of a fever (elevation in temperature) increases the kinetic energy of the molecules, providing enough energy to break chemical bonds. The consequence of high fever may result in the denaturing of proteins and potentially cause the death of the cell (and possibly the death of the individual). 9. Enzymes are catalysts that decrease the energy of activation required for a chemical reaction to proceed. 10. The active site is a region in the enzyme that is the temporary binding site for the substrate to the enzyme. 11. Enzymes are proteins that catalyze metabolic reaction by lowering the activation energy necessary for the reaction. The structure of the protein directly affects its affinity for its specific substrate. (1) Substrate enters the enzyme’s active site and temporarily binds to it, forming an enzyme-substrate complex. (2) Binding of substrate into the active site induces conformational changes in the enzyme; this response is referred to as the induced-fit model of enzyme function. (3) Chemical bonds in the substrate are stressed by changes in the enzyme shape. This lowers the Ea, (activation energy) so that bonds in the substrate(s) are more easily broken and new chemical bonds may be formed. (4) A new molecule (called [a] product[s]) is released from the enzyme. Inorganic cofactors are attached to enzymes and may be required for the normal function of some enzymes. 12. The name of an enzyme is usually based upon the name of the substrate or the product involved in the chemical reaction, or sometimes the name of the enzyme subclass. The suffix -ase is added to the final word of the name. 13. The rate of an enzyme-catalyzed reaction may be increased as the concentration of substrate is increased, until all of the enzyme molecules are saturated. Enzymes function most efficiently at their optimal temperature. Decreasing temperature from an enzyme’s optimum range will decrease its activity. Increasing temperature increases the rate of the reaction until enzymes denature. Changing pH in either direction (increase or decrease) from its optimal pH will readily denature the protein as the change in hydrogen ion concentration interferes with electrostatic interactions within the enzyme, denaturing it. 14. Inhibitors prevent an enzyme from converting substrate to product. Competitive inhibitors affect enzyme activity by competing with substrates at the active site of the enzyme. Noncompetitive inhibitors do not resemble the
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substrate, but they inhibit an enzyme by binding to a site on the enzyme other than the active site (a site called the allosteric site). This modulates the shape of the enzyme altering the shape of its active site. 15. A metabolic pathway is formed by numerous enzymes. Each enzyme catalyzes one progressive change to its specific substrate molecule and then releases the product. Thus, the product of one enzyme becomes the substrate of the next enzyme. Negative feedback is a means to regulate the activity of metabolic pathways. The product from a metabolic pathway acts as an allosteric inhibitor to turn off an enzyme early in the pathway and regulate enzyme activity. 16. Phosphorylation (the adding of a phosphate group) and dephosphorylation (the removal of a phosphate group) are processes that regulate enzymes by turning on some enzymes and turning off other enzymes. 17. The overall chemical reaction for cellular respiration of glucose is: C6H12O2 + 6 O2 → 6 CO2 + 6 H2O. The oxidation of glucose, an exergonic reaction, results in a step-by-step enzymatic breakdown of glucose with the accompanying release of energy to synthesize ATP. If oxygen is available, glucose is completely broken down and carbon dioxide and water are formed. 18. The four stages of cellular respiration are (1) glycolysis within the cytosol of the cell, and three other stages which are (2) the intermediate stage, (3) the citric acid cycle (or Krebs cycle), and (4) the electron transport system, all of which occur within the mitochondria. 19. Glycolysis is a process that occurs within the cytosol and does not require oxygen. The net reaction entails the breakdown of glucose (a 6-carbon molecule) into two pyruvate molecules (each a 3-carbon molecule). The reaction involves the initial input of two molecules of ATP and yields four molecules of ATP, for a net yield of two molecules of ATP. Two molecules of NAD+ are also reduced to form NADH (and H+) from energy released during the oxidation of glucose. 20. Pyruvate may either enter a mitochondrion (if sufficient oxygen is available) to be completely oxidized to carbon dioxide [with the energy released in its chemical bonds] or (if oxygen is lacking) be converted to lactate (a process described in later section in detail). 21. The intermediate stage of cellular respiration is an aerobic process (requires oxygen) that occurs within mitochondria, which “links” the metabolic pathway of glycolysis (that occurs in the cytosol) with the metabolic pathway of the citric acid cycle. During this process CO2 is released from pyruvate (through decarboxylation) and two electrons and a hydrogen ion are transferred to NAD+ to form. (NOTE: this process would occur twice for each glucose molecule). 22. The citric acid cycle is an aerobic process that occurs within the matrix of mitochondria. It uses acetyl CoA as the initial substrate and forms two CO2 molecules and one CoA molecule as the products. The oxidation of acetyl CoA yields: one molecule of ATP, three molecules of NADH, one molecule of FADH2. (NOTE: this process would occur twice for each glucose molecule). 23. Cellular respiration of one molecule of glucose yields: two molecules of ATP and two molecules of NADH during glycolysis, two molecules of NADH during the intermediate stage (per original glucose molecule), two molecules of ATP, six molecules of NADH, two molecules of FADH2 during the citric acid cycle (per original glucose molecule). 24. NADH and FADH2 serve as coenzymes to temporarily hold energy by binding electrons and hydrogen released during the breakdown of glucose during glycolysis, the intermediate stage, and the citric acid cycle. These coenzymes hold the electrons until the electrons are transferred to the electron transport chain, which allows the formation of ATP through oxidative phosphorylation. 25. The three primary steps of the electron transport system are the following: (1) Electrons are transferred from coenzymes to O2, (2) Proton gradient is established, and (3) Proton gradient is harnessed to form ATP.
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26. Glycolysis yields a net of two molecules of ATP for every molecule of glucose. Under aerobic conditions the complete oxidation of one molecule of glucose yields a net of 30 molecules of ATP. 27. In conditions of insufficient oxygen, pyruvate is converted to lactate in the cytosol. This facilitates the regeneration of two molecules of NAD+, which can then be utilized to continue with the glycolysis of more glucose, yielding limited amounts of ATP (2 ATP per glucose). 28. Fatty acids are enzymatically changed two carbon units at a time to form acetyl CoA. This is called betaoxidation of fatty acids. Acetyl CoA is oxidized within mitochondria (through the intermediate stage and the citric acid cycle). Thus, because processes that occur within mitochondria require oxygen, fatty acids can only be oxidized is sufficient oxygen is available.
Answers to “Do You Know the Basics?” 1. A Feedback: Chemical energy is converted to mechanical energy. Energy from the hydrolysis of ATP (which releases chemical energy from the high energy bond between the second and third phosphate) is used to move a body part in response to an applied force exerted by the muscle contraction. 2. A Feedback: Oxidation-reduction reactions involve the exchange of electrons between the oxidizing and the reducing agent. 3. B Feedback: Increasing (or decreasing) pH interferes with electrostatic interactions within the enzyme, causing denaturation of the enzyme (and a subsequent decrease in enzyme activity). 4. C Feedback: Since ATP does not bind to the active site of phosphofructokinase, it is not a competitive inhibitor. It is an example of an allosteric/noncompetitive inhibitor. 5. D Feedback: Enzymes are very specific for their substrate and are therefore each enzyme is capable of catalyzing only one specific reaction. 6. A Feedback: Glycolysis yields two molecules of pyruvate from one molecule of glucose. 7. D Feedback: NAD+ and FAD are coenzymes involved in oxidation-reduction reactions where they bind electrons and hydrogen that are released from both glucose and its (glucose's) breakdown products. 8. A Feedback: Glycolysis is able to continue when there is insufficient oxygen available because oxygen is not required (i.e., glycolysis is not aerobic). 9. C Feedback: One molecule of glucose may yield a net of 2 molecules of ATP if insufficient oxygen is available and a net of 30 molecules of ATP if sufficient oxygen is present. 10. D Feedback: Oxidative phosphorylation involves the transfer of electrons from NADH and FADH2 to oxygen in the electron transport chain, the establishment of a proton gradient through the use of energy from electrons passed along the electron transport chain, and finally using the proton gradient to form ATP as H+ moves down its
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concentration gradient and is transported across the inner mitochondrial membrane by ATP synthetase to form bonds between ADP and Pi. 11. Chemical energy is energy stored in chemical bonds; it is a form of potential energy. Energy stored in glycogen or triglycerides represents chemical energy. The remaining forms of energy are classified as forms of kinetic energy. Electrical energy is the movement of charged particles such as electrons along a wire or the propagation of an impulse in a neuron (nerve cell). Mechanical energy involves the movement of an object due to an applied force; muscle contraction is an example of mechanical energy. Sound energy is movement of compressed molecules through a medium (e.g., air) that is initiated by a vibrating object; vibration of the vocal cords of the larynx is an example. Radiant energy is the movement of electromagnetic waves that travel in the universe and vary in wavelength and frequency; visible light that is perceived by the eye is an example of radiant energy. 12. Chemical reactions are classified as reactions that cause (1) changes in chemical structure, (2) changes in chemical energy, and (3) whether the reaction is irreversible or reversible. Oxidation-reduction reactions are exchange reactions during which electrons are transferred from one substance to another. 13. ATP cycling is the continuous formation of ATP (from ADP and Pi) during cellular respiration and then the splitting of ATP back into ADP and Pi for the energy-requiring cellular processes. 14. Enzymes are globular proteins that catalyze metabolic reactions (both decomposition and synthesis reactions) by lowering the activation energy necessary for the reaction. The substrate enters the active site of the enzyme, and the enzyme temporarily binds with the substrate to form an enzyme-substrate complex. Entry of the substrate into the active site induces the conformation (structure) of the enzyme to change slightly, resulting in an even closer fit between substrate and enzyme. This response is referred to as the induced-fit model of enzyme function. Stress on chemical bonds in the substrate molecule is caused by the change in enzyme shape. Consequently, this stress lowers Ea, and the bonds in the substrates are more easily broken, permitting new chemical bonds to be formed. The newly formed molecule, now called the product, is released from the enzyme. The enzyme is then free to repeat the process again and again with other substrates. 15. A metabolic pathway consists of a series of enzyme-catalyzed reactions. The product of one enzyme becomes the substrate of the next enzyme in the metabolic pathway. Often the final product of the pathway serves as an allosteric inhibitor of enzymes within the pathway, causing a conformation change in the protein. This rearrangement may affect the affinity for the substrate at the enzymes’ active sites, thereby providing for negative feedback within the pathway. 16. Glycolysis is a process that occurs within the cytosol of a cell and does not require oxygen. The net reaction entails the breakdown of glucose (a 6-carbon molecule) into two pyruvate molecules (each a 3-carbon molecule). The reaction involves the initial input of two molecules of ATP and yields four molecules of ATP, for a net yield of two molecules of ATP. Two molecules of NAD+ are also reduced to form NADH and H+ from electrons and protons released during the oxidation of glucose. 17. If sufficient oxygen is available, pyruvate enters a mitochondrion to complete its aerobic breakdown yielding carbon dioxide and water. It insufficient oxygen is present, pyruvate is converted to lactate in the cytosol. This facilitates the regeneration of two molecules of NAD+, which can then be utilized for continuing the steps of glycolysis to yield two molecules of ATP per glucose molecule. 18. Oxygen serves as the final electron acceptor of the electron transport chain during oxidative phosphorylation. Molecular oxygen (O2) in the mitochondrial matrix is split and each oxygen atom along with electrons from the electron transport chain combine with two hydrogen ions, yielding a molecule of water. 19. The carbon in carbon dioxide is liberated from glucose (or other fuel molecules such as fatty acids) during cellular respiration. 20. Healthy respiratory and cardiovascular systems provide metabolically active tissues with adequate oxygen to drive efficient aerobic respiration (which yields greater amounts of ATP than if there is insufficient oxygen). Tissues deprived of oxygen will not be able to burn fuels efficiently nor produce adequate amounts of ATP.
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Chapter 4 Answers to “What Did You Learn?” 1. Electron microscopy utilizes electrons rather than photons of light to ‘illuminate’ the specimen. This provides greater magnification and improves resolution (the ability to see detail). 2. A human oocyte (which is about 120 micrometers in diameter) is larger than an erythrocyte (which is about 7 to 8 micrometers in diameter). 3. The three main structural features of a cell include the plasma membrane, nucleus, and cytoplasm. The plasma membrane forms the outer, limiting barrier of a cell; the nucleus is the largest structure within a cell, it is enclosed by a nuclear envelope, and it houses both the genetic material (DNA) and a nucleolus; and the cytoplasm that includes the cytosol, organelles, and inclusions. 4. The plasma membrane forms the outer, limiting barrier of the cell and maintains its integrity. 5. Most of the plasma membrane lipids are phospholipid molecules organized into a bilayer. The hydrophobic (“water fearing”) tails of each layer are oriented toward each other, whereas the hydrophilic (“water loving”) heads are exposed to aqueous environments. Therefore, the lipid portion of the plasma membrane is insoluble in water, which ensures that it will not dissolve when it comes into contact with water. 6. Integral membrane proteins are embedded within and extend across the phospholipid bilayer. Transport proteins provide the means for moving materials across the plasma membrane. Transport proteins include channels, carriers, pumps, symporters, and antiporters. 7. O2 and CO2 do not require transporters because they are both small and nonpolar molecules. They can pass through the plasma membrane phospholipid bilayer by simple diffusion. 8. Ions and small polar molecules may be transported across the plasma membrane by facilitated diffusion. Ions diffuse through water-filled protein channels, each of which is specific for one type of ion by a process called channel-mediated facilitated diffusion. Small polar molecules require carrier proteins, which change shape when they bind to the small polar molecules thus permitting transport of the molecule across the membrane by the process called carrier-mediated facilitated diffusion. 9. Osmosis is the passive movement of water through a selectively permeable (semipermeable) membrane. 10. The tonicity of a cell placed into an isotonic solution will not change because both the solution and the cytosol have the same relative concentration of solutes. A cell placed into a hypotonic solution will experience an increase in tonicity because of a net movement of water into the cell. Conversely, a cell placed into a hypertonic solution will lose tonicity because of a net movement of water out of the cell. 11. There is always a net movement of water toward (c) a hypertonic solution. 12. Secondary active transport couples the kinetic energy from the movement of one type of substance (e.g., Na+) down its concentration gradient to move another type of substance against its gradient. Note that these two types of molecules can be moved in the same direction (symport secondary active transport) or in the opposite direction (antiport secondary active transport). 13. A white blood cell engulfing a microbe is an example of phagocytosis. 14. The resting membrane potential (RMP) is the electrical charge difference at the plasma membrane when a cell is at rest. The RMP ranges in value from –50 mV to –100 mV. 15. The resting membrane potential is established by specific types of ions diffusing across the plasma membrane through leak channels: K+ leaks out of a cell and Na+ leaks into a cell. The amount of each ion that diffuses is
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dependent upon both the electrochemical gradient and the number of leak channels present within the plasma membrane. The Na+/K+ pumps maintain the concentration gradients for both Na+ and K+. 16. Cells communicate by direct contact through the interaction of the glycocalyxes of two cells. Examples include: the recognition of cells by the immune system, the interaction of sperm with an oocyte at the onset of fertilization, and the contact inhibition to prevent overgrowth of skin tissue at the site of injury. 17. Enzyme receptors function as protein kinase enzymes and are activated to directly phosphorylate other enzymes (which may either turn the enzyme on or off) in response to the binding of a ligand; G protein-coupled receptors also involve protein kinase activation: however, these enzymes are activated indirectly through the G protein that serves as an intermediate molecule. 18. The endoplasmic reticulum is an extensive interconnected membrane network that varies in shape (e.g. tubules, sacs), but has one continuous lumen. It extends from the nuclear envelope to the plasma membrane. Its membrane surface is a point of attachment for ribosomes and enzymes. Rough endoplasmic reticulum (RER) forms proteins and glycoproteins and the smooth endoplasmic reticulum (SER) synthesizes lipids. Transport vesicles containing these molecules are formed by the pinching off of sections of the ER. The vesicles fuse with the Golgi apparatus. The Golgi apparatus has several elongated, flattened saclike membranous structures called cisternae, which exhibit a distinct polarity: a cis-face that is closer to the ER and a trans-face with larger flattened sacs. The Golgi modifies, packages, and sorts proteins before they are shipped out for different fates. 19. Lysosomes digest unwanted organelles (and also contents of endocytosed vesicles, and the cellular contents following death of the cell). Peroxisomes function in both digestion of molecules (e.g., fatty acids, amino acids) and producing hydrogen peroxide in the process, and the synthesis of specialized lipids (e.g., bile salts). 20. These non-membrane bound organelles have the following functions: (a) proteasomes function in digesting unwanted proteins; (b) the cytoskeleton forms the structural support of a cell; (c) ribosomes synthesize proteins, and (d) centrioles function in cell division. 21. Both microvilli and cilia are cell surface extensions of the plasma membrane supported by protein. (a) Microvilli are thin, microscopic membrane extensions from the surface of the plasma membrane that serve to increase the surface area of a cell for more efficient membrane transport. Microvilli are shorter, wider, and more densely packed than cilia and are supported by microfilament protein. (b) Cilia are small hair-like projections supported by microtubules that function in moving material along the cell surface. They contain both cytoplasm and supportive microtubule proteins, and are enclosed by the plasma membrane. 22. Cellular junctions connect and support cells. (a) Desmosomes provide resistance to mechanical stress at a single point; (b) Gap junctions allow passage of ions between cells, and (c) Tight junctions prevent leakage between cells. 23. Nuclear pores are open passageways formed by proteins that extend through fused regions of the nuclear envelope. They permit the movement of large molecules into or out of the nucleus including protein molecules into the nucleus and RNA molecules out of the nucleus. 24. The nucleolus is a dark-staining, usually spherical body located within the nucleus. It functions in the formation of the large and small ribosomal subunits. 25. DNA in the nucleus forms enormous macromolecules that house most of the genetic material of the cell. DNA is associated with nuclear proteins called histones to form nucleosomes, which are arranged in a loosely coiled structural arrangement called chromatin. (The chromatin strands condense into chromosomes in preparation for cell division.) A gene is a specific, discrete functional unit of DNA, which is responsible for the production of a specific protein. 26. Three major structures are required for transcription: DNA, ribonucleotides, and the enzyme RNA polymerase. Transcription involves the arrangement of ribonucleotides along a functional segment of the DNA template (a gene) to form a new RNA molecule. Within the nucleus, a segment of the DNA unwinds at the gene with the breaking of
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hydrogen bonds in between the two complementary DNA strands. Bases of ribonucleotides are complementary base-paired with bases of the DNA, a process assisted by the enzyme RNA polymerase. 27. A codon is a three nucleotide base unit sequence of mRNA. The anticodon is a three nucleotide base unit sequence of tRNA. The anticodon serves two functions. (1) Its sequence (e.g., UAC) determines the specific amino acid (e.g., methionine) to which a given tRNA attaches, a process facilitated by aminoacyl-tRNA synthetase prior to translation (synthesis) of the protein. (2) The anticodon of each tRNA is to serve as the “adapter site” for binding a tRNA to its complementary codon of an mRNA during translation. 28. Translation (or synthesis of a protein) involves three processes: initiation, elongation, and termination. During initiation, the small subunit, large subunit, mRNA, and the first charged tRNA (tRNA with anticodon UAC and holding methionine amino acid) form a complex. This tRNA is in the P site of the ribosome. During elongation the following steps occur repeatedly: (a) a charged tRNA with its amino acid attached is positioned in the A site of the ribosome. The specific tRNA is based on complementary base pairing of the codon of the mRNA and the anticodon of that charged tRNA. (b) A peptide bond forms between the two amino acids (one in the P site and the other in the A site). (c) At this point the first tRNA is released and the ribosome shifts down one codon on the mRNA. The process continues until a stop codon enters the A site signaling the termination of translation. Termination occurs when a stop codon (UAA, UAG, or UGA) enters the A site to end translation. A release factor enters the A site at this point instead of a charged tRNA. When the ribosome hits the factor bound to the mRNA stop codon, the two subunits of the ribosome are separated from the mRNA and the newly synthesized protein is released. 29. The genetic code of DNA is responsible for directing the synthesis of proteins. 30. Chromatin is an uncoiled arrangement of DNA in the nucleus. It is well suited to facilitate transcription and DNA replication. Chromosomes are highly organized, tightly coiled masses that are a condensed form of DNA, which is better suited for the process of cell division. 31. During the S phase of interphase, double helix strands of each of the 46 chromosomes are replicated. DNA replication entails (1) the unwinding of the DNA double helix, (2) the separation of parent strands by breaking hydrogen bonds between the complementary bases, (3) the assembly of new identical DNA strands by DNA polymerase, which complementarily base-pairs free deoxyribonucleotides using both parent strands as templates, and (4) the restoration of DNA double helix as the DNA double strands form their coiled, helix structure. 32. Two distinct events occur during Mitotic Phase (mitosis, which is the division of the DNA within the nucleus for form two nuclei, and cytokinesis, which is the division of the cytoplasm to form two cells with each having one of the nuclei). MITOSIS: There are four stages in mitosis: [1] Prophase: chromatin supercoils into chromosomes, the nucleolus breaks down and disappears, spindle fibers begin to grow from centrioles, centriole pairs move to opposite poles of the cell, and the nuclear envelope disassembles; [2] Metaphase: chromosomes are aligned in the equatorial plate as spindle fibers attach to the centromere of each chromosome and move them into the center of the cell; [3] Anaphase: spindle fibers move sister chromatids apart toward the cell’s poles (and each sister chromatid, with its own centromere, is now considered a chromosome); and [4] Telophase: chromosomes arrive at each cell pole, chromosomes uncoil, each new nucleus forms a nucleolus, the mitotic spindle breaks up and disappears, and a new nuclear envelope forms around each of the two sets of chromatin. CYTOKINESIS: Division of the cytoplasm between the two newly forming cells – each with their own nucleus. 33. Apoptosis is a process of programmed cell death. DNA is digested into small fragments.
Answers to “Do You Know the Basics?” 1. C Feedback: Not all cells are capable of cell division. All cells are capable of acquiring nutrients, maintaining a plasma membrane, and removing waste.
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2. D Feedback: The plasma membrane is an equal mixture (by weight) of proteins and lipids. Most of its functions are determined by proteins. These include: transport of substances, cell surface receptors, identity markers, enzymes that catalyze chemical reactions, anchoring sites for the cytoskeleton, and cell-adhesion proteins for cell-to-cell attachments. 3. B Feedback: Facilitated diffusion through either a channel or a carrier protein requires a concentration gradient but does not require energy from ATP. The random movement of molecules and ions allows substances to diffuse from where the substance is more concentrated to where it is less concentrated. 4. C Feedback: Since the movement of one substance down its concentration gradient is coupled to the movement of another molecule against its particular gradient, this is an example of secondary active transport. Because both molecules are moving in the same direction, the transport molecule would be a symporter. Thus the process is symport secondary active transport. 5. A Feedback: Lysosomes, the Golgi apparatus, and the endoplasmic reticulum are all composed of phospholipid membranes. Ribosomes are non-membrane bound organelles (composed of protein the rRNA). 6. A Feedback: The smooth endoplasmic reticulum is responsible for lipid synthesis and the detoxification of lipidsoluble molecules such as alcohol. 7. C Feedback: Proteasomes are responsible for degrading malformed, damaged, or obsolete proteins. 8. D Feedback: Transcription forms RNA from DNA. (Translation forms a polypeptide chain from RNA; DNA replication forms new DNA; mitosis is the process of dividing the nucleus during cell replication). 9. A Feedback: Prophase involves all of the preparatory steps necessary prior to nuclear division such as condensation of chromatin to chromosomes, spindle fiber formation, disappearance of the nuclear envelope, and migration of centrioles to opposite poles. 10. B Feedback: DNA within the nucleus is required for protein synthesis and cell division. 11. [1] The plasma membrane is the outer barrier of the cell. It forms the outer, limiting barrier separating the internal contents of the cell from the external environment. [2] The nucleus is the largest structure within the cell and is enclosed by a nuclear envelope. Most of its internal content is the genetic material (DNA). [3] Cytoplasm is a general term for all cellular contents located between the plasma membrane the nucleus. Its primary components are the cytosol, organelles, and inclusions. 12. Proteins associated with the plasma membrane of a cell may function as: (1) transport proteins (including channels, carriers, pumps, symporters, and antiporters) regulating passage into or out of the cell; (2) cell surface receptors that bind ligands for cell communication; (3) identity markers that communicate to other cells that they belong in the body; (4) enzymes that catalyze chemical reactions; (5) anchoring sites for the cytoskeleton; or (6) cell adhesion proteins that bind cells together. 13. [1] Simple diffusion occurs when small nonpolar molecules are able to move through the membrane phospholipid bilayer down their concentration gradient without the need of transport molecules. [2] Facilitated diffusion involves movement of charged ions or polar molecules across the plasma membrane down their
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concentration gradient through either channels (for ions) or by carriers (for polar molecules). [3] Osmosis is a process involving the movement of water down its concentration gradient through a semipermeable membrane. 14. Active transport is a membrane transport process in which a substance is moved up its concentration gradient. Primary active transport involves pumps (e.g., Ca2+ pumps and Na+/K+ pumps) that directly utilize the energy from the hydrolysis of ATP to move solutes against their concentration gradients to maintain concentration gradients at the plasma membrane. Secondary active transport couples the movement of one molecule down its concentration gradient (which provides the energy) to the movement of another molecule against its concentration gradient. Symport secondary active transport is when the two substances move in the same directions, whereas antiport secondary active transport is when the two substances move in the opposite direction. Vesicular transport requires an input of energy to drive the bulk movement of molecules into or out of a cell through vesicles. Exocytosis is the release of contents within a vesicle from the cell into the interstitial fluid. Endocytosis occurs with the invagination of the plasma membrane that results in bringing material into the cell through the formation of a vesicle. The three forms of endocytosis include: phagocytosis (cell eating), pinocytosis (cell drinking), and receptor-mediated endocytosis (bringing in specific type of molecule after it binds to plasma membrane receptors). 15. [1] The endoplasmic reticulum consists of a series of folded membranes within the cytoplasm. (a) The rough endoplasmic reticulum is studded with ribosomes and is involved in protein synthesis, the processing of the new proteins (e.g., adding carbohydrates), formation of peroxisomes, and formation of transport vesicles. (b) The smooth endoplasmic reticulum is responsible for lipid synthesis, processing molecules, the detoxification of lipid-soluble toxins, and the formation of vesicles. [2] The Golgi apparatus consists of a series of flattened membranous sacs, responsible for the synthesis of proteoglycans, modification of proteins, formation of lysosomes, and formation of secretory vesicles. [3] Lysosomes and peroxisomes are small membranous spheres containing metabolic enzymes. (a) Lysosomes contain digestive enzymes that are responsible for the breakdown of cellular structures or ingested materials. (b) Peroxisomes contain enzymes that break down molecules (e.g., fatty acids during beta oxidation) with the accompanying formation of hydrogen peroxide. They also participate in the synthesis of some specialized lipids (e.g., bile salts). [4] Mitochondria are unlike other membrane-bound organelles, because they consist of two distinct membranes, one internal to the other. They are responsible for the majority of ATP synthesis within the cell that occurs through aerobic cellular respiration. 16. (1) Microfilaments are composed of an intertwined actin protein network that lines the inner boundary of the plasma membrane. They are involved in maintaining cell shape, forming internal support of microvilli, participating in cytokinesis, changes to the cell’s shape, and they participate in muscle contraction. (2) Intermediate filaments vary in composition, depending upon the cell type, and are involved in structural support of the cell and stabilization of junctions between them. (3) Microtubules are hollow cylinders composed of long chains of a globular protein called tubulin. They are not permanent structures and may be elongated or shortened as needed. Microtubules help maintain cell shape, organize and move organelles within a cell, form protein components of cilia and flagella, participate in cellular transport of vesicles, and separate chromosomes during cell division. 17. Both cilia and microvilli are projections of the plasma membrane supported by protein. Cilia are relatively small hair-like projections that are supported by microtubule protein. They participate in moving substances past a cell's surface. In comparison, microvilli are shorter, wider, and more densely packed than cilia. They are supported by microfilament protein. Microvilli serve to increase the cell's surface area. 18. Transcription occurs within the nucleus and is the process by which DNA is converted to mRNA during gene expression. Transcription is organized into three steps: initiation, elongation, and termination. During initiation the RNA polymerase attaches to the promoter region of a gene that is to be transcribed. Elongation involves RNA polymerase enzyme assisting complementary base pairs of free ribonucleotides with the DNA with a phosphodiester bond formed between the ribonucleotides of the new RNA strand. Termination of transcription occurs as the RNA polymerase reaches the terminal region of the gene and releases the newly formed RNA strand (and DNA completely closes). Translation (or synthesis of a protein) involves three processes: initiation, elongation, and termination. During initiation, the small subunit, large subunit, mRNA, and the first charged tRNA (tRNA with anticodon UAC and holding methionine amino acid) form a complex. This tRNA is in the P site of the ribosome. During elongation the following steps occur repeatedly: (a) a charged tRNA with its amino acid attached is positioned in the A site of the ribosome. The specific tRNA is based on complementary base pairing of the codon of the mRNA and the anticodon
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of that charged tRNA. (b) A peptide bond forms between the two amino acids (one in the P site and the other in the A site). (c) At this point the first tRNA is released and the ribosome shifts down one codon on the mRNA. The process continues until a stop codon enters the A site signaling the termination of translation. Termination occurs when a stop codon (UAA, UAG, or UGA) enters the A site to end translation. A release factor enters the A site at this point instead of a charged tRNA. When the ribosome hits the factor bound to the mRNA stop codon, the two subunits of the ribosome are separated from the mRNA and the newly synthesized protein is released. 19. DNA directly controls cell processes because it is in charge of the synthesis of all cell proteins. By regulating gene expression, the presence of metabolic enzymes, receptors, or structural proteins may be affected. Because enzymes (which are formed under the direction of DNA) are responsible for the metabolic processes of the cell (digestion and synthesis chemical reactions), thus DNA is also indirectly responsible for these processes as well. 20. The cell cycle is organized into interphase (which includes G1, S, and G2) and mitotic phase (which is divided into mitosis and cytokinesis). G1: During the G1 phase cells grow and produce new organelles and other structures needed for DNA replication. S phase: During the S phase the DNA is replicated, a process that involves DNA polymerase enzyme. DNA polymerase catalyzes DNA replication by assisting free deoxyribonucleotides to complementarily base-pair with exposed bases of the DNA strands. All 46 strands of DNA are replicated (and the replicated strands called sister chromatids remain attached at centromeres). G2: During the G2 phase, centriole replication is completed (having produced two centriole pairs present within the cell) and enzymes and other structures needed for cell division are synthesized. The mitotic phase consists of two overlapping events. Mitosis is nuclear division that results in the formation of two nuclei within the cell whereas cytokinesis is the dividing of the cytoplasm and plasma membrane resulting in splitting the cell into two daughter cells—each with their own nucleus. The four stages in mitosis include: [1] Prophase: chromatin supercoils into chromosomes, the nucleolus breaks down and disappears, spindle fibers begin to grow from centrioles, centriole pairs move to opposite poles of the cell, and the nuclear envelope disassembles; [2] Metaphase: chromosomes are aligned in the equatorial plate as spindle fibers attach to the centromere of each chromosome and move them into the center of the cell; [3] Anaphase: spindle fibers move sister chromatids apart toward the cell’s poles (and each sister chromatid, with its own centromere, is now considered a chromosome); and [4] Telophase: chromosomes arrive at each cell pole, chromosomes uncoil, each new nucleus forms a nucleolus, the mitotic spindle breaks up and disappears, and a new nuclear envelope forms around each of the two sets of chromatin.
Answers to “Can You Apply What You’ve Learned?” 1. B Feedback: Lysosomes are small membranous sacs containing digestive enzymes that are responsible for digestion of unneeded or unwanted substances. 2. B Feedback: Receptor-mediated endocytosis is required to remove LDL particles from the blood. 3. D Feedback: Cancer involves uncontrolled cell division (or mitosis). 4. C Feedback: Testosterone is a hormone that requires a receptor to initiate metabolic events within the cell. 5. A Feedback: Protein synthesis is a two-step process: first transcription, then translation.
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Answers to “Can You Synthesize What You’ve Learned?” 1. The student is looking at areolar connective tissue. Areolar connective tissue is found in the papillary layer of the dermis, as well as the subcutaneous layer of the skin. It also surrounds organs, nerve cells, some muscle cells, and blood vessels. 2. The articular cartilage at the ends of long bones consists of hyaline cartilage. Chondroitin sulfate is a component of the hyaline cartilage matrix. Therefore the supplement may help reduce the effects of arthritis in the joint, if that is indeed the cause of the pain.
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Chapter 6 Answers to “What Did You Learn?” 1. The thorn would first penetrate the stratum corneum, the most superficial layer of the epidermis. It would then puncture the stratum lucidum, the stratum granulosum, the stratum spinosum, and finally the stratum basale. 2. Keratinization occurs due to the production of keratin, a hardening agent, within keratinocytes. Within the stratum spinosum, the cells fill up with keratin, and the nucleus and organelles become polymerized within the protein, eventually killing the cell. The cells then rupture, releasing keratin at the stratum granulosum. The subsequent superficial layers of the stratum lucidum and corneum consist of ruptured keratinocytes embedded in keratin. This provides for a hardened waterproof barrier between the external environment and the dermis below. 3. Hemoglobin turns red when bound to oxygen. As blood vessels bring hemoglobin close to the surface within the dermis, the skin takes on a reddish hue. 4. Friction ridges increase friction on contact with the skin. It has been hypothesized that they may also provide for pliability at the surface of the skin. 5. The papillary layer, composed primarily of areolar connective tissue, is the most superficial layer of the dermis. The reticular layer lies deep to the papillary layer, makes up the majority of the thickness of the skin, and is predominantly dense irregular connective tissue. Dermal papillae, the folds within the papillary layer, contain numerous capillaries and tactile receptors. The reticular layer contains most of the structures associated with the dermis, such as the hair follicles, sebaceous and sweat glands, nerves, and blood vessels. 6. Tension lines correspond to the direction of collagen bundles within the dermis of the skin. They are relevant clinically as these represent the optimum direction for an incision through the skin. An incision perpendicular to the tension lines can be easily pulled apart and is more likely to result in scarring. 7.
The subcutaneous layer, deep to the skin, consists predominantly of areolar and adipose tissues.
8. Vitamin D3, also called cholecalciferol, is synthesized from a steroid precursor by the keratinocytes when they are exposed to ultraviolet radiation. 9. The skin is water resistant, but not entirely waterproof. Some water is always lost through the skin when you sweat. More water is typically lost through transpiration, a process in which fluids slowly penetrate through the epidermis and then evaporate into the surrounding air. 10. The skin can dissipate heat by vasodilating the blood vessels in the dermis. This allows for more warm blood to travel close to the body surface, and the heat from the blood to dissipate through the skin. In addition, sweating allows fluid to be released on the surface of the skin, and when that fluid evaporates, it cools the body. 11. The hyponychium is a thick layer of stratum corneum, deep to the free edge of the nail. The eponychium, or cuticle, is a small fold of skin that covers the proximal edge of the body of the nail. 12.
The three zones of hair are the hair bulb, the root, and the shaft.
13. Hair on the scalp protects from exposure to the sun. Hairs within the nostrils, ears, or eyelashes protect the respective openings from debris. The eyebrows help to keep sweat out of the eyes. On a cold day the hair on the scalp also acts as insulation, preventing the loss of body heat. 14. Merocrine sweat glands are distributed throughout the body, whereas apocrine glands are primarily associated with hair follicles in the axillary, genital, and anal regions. Sweat produced by merocrine glands contains over 99% water with salts and trace amounts of metabolic waste. Its primary function is thermoregulation by evaporative cooling. Sweat from apocrine glands, along with water and salts, also contains an abundance of proteins and lipids.
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