Ellie Tang Mitosis, Meiosis, and Cancer Guided Notes Chapters 8 and 11 8.1-8.3 ● Sexual Reproduction: ○ The creation of offspring that generally resemble their parents, with the participation of sperm and egg. ● Asexual Reproduction: ○ The creation of genetically identical offspring by a single parent, without the participation of sperm and egg ● Binary Fission: ○ How Prokaryotes (bacteria and archaea) reproduce, “dividing in half” ● Chromosomes: ○ The structure that contains most of the organisms DNA 8.4 ● Most of the time, chromosomes exist as a diffuse mass of long, thin fibres called chromatin (a combination of DNA and Protein molecules). ● When are compact, distinct chromosomes formed? ○ When they are preparing to divide ● Each eukaryotic chromosome contains one long DNA molecule bearing hundreds or thousands of genes and protein molecules. ● When DNA of each chromosome is replicated, the result is that each chromosome now consists of two copies called sister chromatids. They are joined together at a narrow “waist” called the centromere. 8.5 (What is the cell cycle?) ● Stages of the cell cycle ○ Interphase: ■ 1. G1 phase, “First gap” - The cell grows ■ 2. S phase - The cell continues to grow as it copies its chromosomes ■ 3. G2 phase, “second gap” - Grows more as it completes preparations for division ○ Mitosis Phase:
■ 1. Mitosis - the nucleus and its contents, including the duplicated chromosomes, divide and are evenly distributed to form two daughter nuclei. ■ 2. Cytokinesis - the cytoplasm is divided into two ● What stage does the cell spend most of its life in? What happens to the cell during this time? ○ Interphase 8.6 (Summarise each stage of MITOSIS) ● Prophase/Prometaphase: ○ Prophase: changes occur in both the nucleus and the cytoplasm. In the nucleus, the chromatin fibres become more tightly coiled and folded, forming discrete chromosomes that can be seen with the light microscope. The nucleoli disappear. Each duplicated chromosome appears as two identical sister chromatids joined together, with a narrow “waist” at the centromere. In the cytoplasm, the mitotic spindle begins to form as microtubules rapidly grow out from the centrosomes, which begin to more away from each other. ○ Prometaphase: The nuclear envelope breaks into fragments and disappears. Microtubules emerging from the centrosomes at the poles (ends) of the spindle reach the chromosomes, now highly condensed. At the centromere region, each sister chromatid has a protein structure called a kinetochore (on each side of the waist). Some of the spindle microtubules attach to the kinetochores, throwing the chromosomes into agitated motion. Other spindle microtubules make contact with microtubules coming from the opposite pole. Forces exerted by protein “motors” associated with spindle microtubules move the chromosomes towards the centre of the cell ● Metaphase: ○ The mitotic spindle is fully formed, with its poles at opposite ends of the cell. The chromosomes convene on the metaphase plate, an imaginary plane equidistant between the two poles of the spindle. The centromeres of all the chromosomes, the kinetochores of the two sister chromatids face opposite poles of the spindle. The microtubules attached to a particular chromatid all come from one pole of the spindle, and those attached to its sister chromatid come from the opposite pole ● Anaphase: ○ Begins when the two chentresomes of each chromosome come apart, separating the sister chromatids. Once separate, each sister chromatid is considered a fully-fledged (daughter) chromosome. Motor proteins of the kinetochores, powered by ATP, “walk” the daughter chromosomes centrosome-first along the microtubules toward opposite poles of the cell. As this happens, the spindle
microtubules attached to the kinetochores shorten. However, the spindle microtubules not attached to chromosomes lengthen. The poles are moved farther apart, elongating the cell. Anaphase is over when all of the chromosomes have reached the two poles of the cell ● Telophase: ○ Roughly the reverse of prophase. The cell elongation that started in anaphase contines. Daughter nuclei appear at the two poles of the cell as nuclear envelopes form around the chromosomes. Meanwhile, the chromatin fibre of each chromosome uncoils, and nucleoli reappear. At the end of telophase, the mitotic spindle disappears. Mitosis, the equal division of one nucleus into two genetically identical daughter nuclei, is now finished. ● What happens during Cytokinesis? ○ The division of the cytoplasm, usually occurs along with telophase. With two daughter cells completely separating soon after the end of mitosis. In animal cells, cytokinesis involves a cleavage furrow, which pinches the cell in two. 8.7 ● Explain the difference between cytokinesis in animal cells and plant cells. ○ In Animal cells, cytokinesis occurs as the cleavage is furrowed. In plant cells, a central wall is created in order to split the cell in two. 8.8 ● Define the following terms: ○ Growth factor: ■ A protein secreted by certain body cells that stimulates other cells to divide ○ Density-dependent inhibition: ■ A phenomenon where crowded cells stop dividing ○ Anchorage dependence: ■ Animal cells must be in contact with a solid surface to divide 8.9 (How a Growth Factor Signals the Cell Cycle Control System) ● Using your book, label and explain this figure.
8.10 (Define the following terms about cancer) ● Tumour: ○ An abnormally growing mass of body cells ● Benign Tumour: ○ When the lump formed of original cells stays at the original site (doesn’t move) ● Malignant Tumour: ○ When the tumour moves from the original site and spreads to other neighboring tissues. This can interrupt organ function and displace normal tissue. ● Metastasis: ○ The spread of cancer cells via the circulatory system beyond their original site ● Carcinomas: ○ Cancers that originate in the external or internal coverings of the body (skin, lining of intestines) ● Sarcomas: ○ Cancers that arise in tissues that support the body (bone, muscle) 8.11 ● What are three reasons for mitosis? ○ 1. Asexual Reproduction ○ 2. Growth of the organism ○ 3. Cell replacement
8.12 ● A typical human somatic cell contains 46 chromosomes, or 23 matched pairs. The matched pairs are called homologous chromosomes (they both carry genes controlled the same inherited characteristics). ● Each gene is located at a specific place, or locus, on a chromosome. ● What are the sex chromosomes? ○ The 23rd set of chromosomes, the X and Y chromosomes, they decide the individual's sex ● What are autosomes? ○ The other 22 sets of chromosomes. 8.13 ● Any cell with two homologous sets of chromosomes is called a diploid cell. ● What are gametes? ○ The female and male sex cells ● These cells have a single chromosomes set, or a haploid number of chromosomes. ● Define fertilisation and zygote: ○ Fertilization: the process in which the haploid sperm cell and a haploid egg cell come together and fuse ○ Zygote: the fertilized egg cell (diploid) 8.14 ● What is Meiosis? ○ Meiosis is a type of cell division that produces the haploid gametes in diploid organisms ● Summarise the events of Meiosis I: ○ Interphase: ■ Pre-Meiosis, this is similar to the interphase in mitosis, the chromosomes replicate and form sister chromatids which are connected at the centromere. ○ Prophase I: ■ This is where ~90% of the time spent in meiosis is spent. The chromatin form chromosomes, the homologous chromosomes come together to form pairs resulting in a 4 chromosome structure known as a tetrad. This is