BIOLOGY - CLUTCH CH.12 - CELL DIVISION.

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2 CONCEPT: CELL DIVISION Cell division is the process by which one cell splits into two or more daughter cells. Cell division generally requires that cells produce enough materials, such as organelles and DNA, so that both daughter cells are able to survive and function properly. Cell division usually is part of a larger cell cycle that involves the preparation for, and regulation of division. G1, S, and G2 phases are collectively known as interphase. The cell grows during the interphase, producing new organelles and cytosol (cytoplasm). The cell produces a copy of its DNA during S phase. Mitosis is the process by which some cells divide their genetic material Cytokinesis division of the cytoplasm, finishes immediately after mitosis Page 2

3 CONCEPT: CELL DIVISION Prior to cell division, a cell s genome must be replicated, condensed, and organized into discrete chromosomes. Genome the complete set of an organism s DNA Chromatin an organized structure of DNA, RNA, and proteins Chromosomes discrete units of chromatin Replicated chromosomes are held together at the centromere, and are called sister chromatids. Mitochondria and chloroplasts have their own DNA, and replicate independently of the cell during interphase. They are distributed between the daughter cells during cytokinesis. Page 3

4 CONCEPT: CELL DIVISION Prokaryotes, and some unicellular eukaryotes, undergo a type of cell division call binary fission. Prokaryotes do not undergo mitosis during cell division. Prokaryotes genome is made up of a single large circular loop of DNA, and possibly additional plasmids. Plasmids small loops of DNA which contain a few genes, and replicate independently of chromosomal DNA During Binary fission the cell replicates its DNA, grows much larger, then splits in half. Prokaryotic chromosomes contain a single origin of replication A ring of proteins forms around the center to pinch the cells in half forming a septum. Page 4

5 PRACTICE: 1. Chloroplasts and mitochondria are evenly distributed during of the cell cycle. a. G2 b. M c. G1 d. there is no mechanism to distribute them evenly 2. Which of the following does not occur during interphase? a. G1 b.g2 c. S d. M 3. Nuclear division in eukaryotes is called while the process of bacterial cell division is called. a. meiosis cytokinesis b. mitosis cytokinesis c. meiosis binary fission d. mitosis binary fission 4. Which of the following is the correct order of cell cycle phases? a. G1 à G2 à S à M b. G1 à S à G2 à M c. G1 à S à M à G2 d. S à G1 à G2 à M Page 5

6 CONCEPT: MITOSIS The cell cycle is made up of 4 phases: G1: Cell growth S: Synthesis of DNA, and cell growth G2: Cell growth M: Mitosis and cytokinesis Mitosis occurs in five stages, with cytokinesis occurring simultaneously, and ending the division process. 1. Prophase 2. Prometaphase 3. Metaphase 4. Anaphase 5. Telophase Page 6

7 CONCEPT: MITOSIS G2: The centrosome, microtubule organizing center of the cell, has duplicated The chromosomes have duplicated, but are not condensed The nuclear envelope is intact The nucleoli (complexes of protein and RNA that synthesize rrna from DNA) are intact Prophase: The chromatin fibers condense into visible chromosomes, or pairs of sister chromatids The nucleoli disappear The spindle apparatus begins to form, pushing the centromsomes away form each other Page 7

8 CONCEPT: MITOSIS Prometaphase: The chromosomes have condensed further and have a kinetochore, a protein structure at the centromere The nuclear envelope fragments Some microtubules attach to the kinetochores of sister chromatids Some microtubules attach to those from the opposite pole Metaphase: The chromosomes are aligned on the metaphase plate The centrosomes are at opposite poles of the cell Each kinetochore of a pair of sister chromatids has microtubules from opposite poles attached to it Page 8

9 CONCEPT: MITOSIS Anaphase: The proteins binding the sister chromatids are cleaved Microtubules attached at the kinetochore pull the sister chromatids apart, making them individual chromosomes Microtubules from opposite poles attached to each other lengthen, pushing the poles further apart Telophase: The chromosomes become less condensed Two nuclei form in the cell from the fragments of the nuclear envelope and endomembrane system The nucleoi reappear The spindle apparatus disassembles Page 9

10 CONCEPT: MITOSIS Cytokinesis occurs during mitosis, and completes the cytoplasmic division between the daughter cells after telophase. Animal cells form a cleavage furrow, a groove in the cell near the metaphase plate. The cleavage furrow is formed by the contractile action of the microfilament actin, and the motor protein myosin. Plant cells form a cell plate, a structure formed from vesicles from the Golgi apparatus and cell wall materials When the spindle apparatus assembles, some of the microtubules of the cytoskeleton disassemble to form them. Microtubules form from the polymerization of tubulin, which has a plus and minus end. During mitosis microtubules pull chromosomes apart, there are two theories as to how: Pac-man theory: motor proteins walk chromosomes along microtubules that disassemble from the (+) end as they pass Reel-in theory: disassemble at the (-) end, pulling in the chromosomes attached to the (+) end Page 10

11 CONCEPT: MITOSIS PRACTICE: 1. The microtubule framework that arises during cell division and moves chromatids apart is the. a. aster b. centriole c. spindle apparatus d. centromere 2. During the chromatids are pulled to the ends of the spindle. a. interphase b. anaphase c. metaphase d. prophase e. telophase 3. Cytokinesis follows after the stage in mitosis. a. prophase b. interphase c. G1 d. anaphase e. telophase 4. You are examining cells that have mutations that effect anaphase. What are you looking for? a. the centrosomes do not move towards the poles b. the poles do not move apart c. the spindle apparatus does not disassemble d. sister chromatids remain joined Page 11

12 CONCEPT: REGULATION OF CELL CYCLE The cell cycle is highly regulated, as abnormal cell growth can lead to cancer. The cell cycle control system uses molecular signals to drive cell growth, and has checkpoints to halt it if necessary. Checkpoints that act as gates between the phases of the cell cycle. Proteins that fluctuate in concentration and activity are the core of the cell cycle control system. Cyclins proteins that cyclically fluctuate in concentration in the cell Cyclin-dependent kinases (Cdks) the activity of these kinases fluctuates with cyclin concentration, while their concentration remains stable through the cycle Page 12

13 CONCEPT: REGULATION OF CELL CYCLE Maturation-promoting factor (MPF) is a Cdk that is highly involved in the control of mitosis. MPF plays a role in the G2 checkpoint by phosphorylating a bunch of proteins, leading to mitosis MPF is turned off by negative feedback in anaphase M checkpoint 1 checks spindle attachments to ensure each cell gets the right amount of chromosomes M checkpoint 2 involves MPF, and controls the passage from M into G1 Page 13

14 CONCEPT: REGULATION OF CELL CYCLE G1 checkpoint is strict and checks for size, resources, and DNA damage. Cells that will no longer divide pass from G1 to G0, some cells can even be called back to G1. DNA damage causes the tumor suppressor p53 to activate genes that halt the cell cycle until the DNA is repaired. x If the damage cannot be repaired, the cell dies via apoptosis. Cancer cells do not stop dividing, do not obey the cell cycle control system, and can form masses called tumors. Metastasis is when cancer cells spread from one site to another distant one Malignant tumors spread, benign tumors do not Page 14

15 CONCEPT: REGULATION OF CELL CYCLE Social control cells divide in response to signals from other cells Growth factors are proteins released by cells that cause other cells to divide. Platelet-derived growth factor (PDGF) has an RTK receptor, and allows cells to pass G1 and divide. Density-dependent inhibition crowded cells stop dividing Page 15

16 CONCEPT: REGULATION OF CELL CYCLE PRACTICE: 1. Which proteins fluctuate in concentration during the cell cycle? 2. Cdk stands for? 3. What proteins do cells release to stimulate other cells to divide? 4. Which of the following is true of cancer cells: a. all cancer cells result from one type of mutation b. cancer cells obey social controls c. cancer cells are regulated by the cell cycle d. cancer cells stop growing e. none of the above 5. What is the difference between a benign tumor, and a malignant one? Page 16