Cell Division and Cell Cycle Past Paper 2024 PDF

The Cell-Division Cycle and Meiosis Chapter 18 and 19 pgs. 635-666 and pgs. 677-689 November 27, 2024 All images are taken from the Essential Cell Biology 5th edition textbook, unless otherwise noted Essential Cell Biology, Fifth Edition Copyright © 2...

The Cell-Division Cycle and Meiosis Chapter 18 and 19 pgs. 635-666 and pgs. 677-689 November 27, 2024 All images are taken from the Essential Cell Biology 5th edition textbook, unless otherwise noted Essential Cell Biology, Fifth Edition Copyright © 2019 W. W. Norton & Company Learning Objectives 1. Compare and contrast mitosis and meiosis. Address when, where, and why, each occurs. 2. Investigate the roles of the mitotic spindle, microtubules, actin, myosin, kinetochores, condensin, and cohesins in mitosis, meiosis, and cytokinesis. 3. Distinguish the stages of mitosis or meiosis when presented with descriptions or figures. 4. Describe the evolutionary advantage of sexual reproduction and analyze the processes that lead to genetic variation. 5. Illustrate ways in which meiosis fails to separate chromosomes correctly, and what are the consequences of nondisjunction. 2 Learning Objectives 6. Differentiate the ways cells regulate progression through the cell cycle. 7. Explain how cyclins, cyclin-dependent protein kinases (Cdk), cyclin dependent kinase inhibitors (Cki), Rb, E2F, and p53 coordinately regulate the promotion or inhibition of cells through the cell cycle. 8. Predict what would happen if any of the proteins that regulate the cell cycle was mutated, providing evidence to support your prediction. 3  Let’s start off with the more familiar concepts of mitosis and meiosis LO 3 Exam prep: Can you identify the different stages of mitosis in the figure above? 4  · Whensteps Activity 1 - Mitosis vs. Meiosis · Where It is important to differentiate the processes of mitosis and meiosis. Work with your group members to define the processes, explain them individually, then compare and contrast the two processes. You should address when and where these processes occur as well as describing the sequence of events in mitosis and meiosis. You may use pipe cleaners to help understand the differences in the two processes (each pipe cleaner represents a chromatid). By the end of the activity you should be able to explain the stages of mitosis vs. meiosis, explain the similarities and differences, and be able to identify which stage of mitosis or meiosis a cell is in based on a description or figure. Completing this activity will help you to meet learning objectives 1, 2, and 3! 5 LO 1, 2, & 3 A note on mitosis/meiosis terminology... Sister Chromatids ≠ Homologous chromosomes Exact copies, generated during S phase. Similar, but not the same. What you inherited from mom, vs. dad. 6 LO 1 Image from Campbell Biology, Pearson Education Mitosis vs Meiosis Why? Where? 7 LO 1 Mitosis Review 8 LO 1, 2, & 3  Meiosis I 9 LO 1, 2, & 3 Figure from Campbell Biology, Pearson Education  Meiosis II 10 LO 1, 2, & 3 Figure from Campbell Biology, Pearson Education  Mitosis vs. Meiosis - separating crossing over · Occurs diploid alls And phose I the r exact - separation of Sister chromatics Copres hoploid # of gametes ↳ A the # op chromosomes (23) Figure from Campbell Biology, Pearson Education 11 LO 1, 2, & 3 If meiosis did not occur in sexually reproducing organisms, then: a. growth of the zygote would be halted. b. mitosis would be sufficient. c. gametes would remain haploid. d. ⑧ chromosome number would double in each generation. e. eggs would be haploid, but sperm would be diploid. 12  LO 4 Sexual reproduction leads to genetic variation! Why that matters - the banana story Crandom Song) Yes, we have no bananas Gros Michel banana - disease/fungus predominant banana same genetic Material so no resistance - - before 1950. Fusarium wilt or Panama disease Today, the Cavendish is the & Cultivated through asexual [ reproduction. dominant cultivar. It’s also cultivated asexually.13  ⑪ Genetic variation is maintained through random mating, ③ crossing over, and independent (chromosomal) assortment ② · Genetic Variation Maintained Crossing creates Variation in parents doesn't genes so what you · Egg get isn't some drymar Chose which fertilizi Sperm Image from: https://www.genome.gov/genetics-glossary/Crossing- Over Population bottleneck = prophes I & possibilities consequence of - dif hour chromosomes non-random mating. align on metophase plate It reduces genetic variation. Image from: 14 LO 4 https://www.nps.gov/articles/bison-bellows-12-3-15.htm Image from: Campbell Biology, Pearson Education Crossing over ONLY occurs in Prophase I of Meiosis Non-sister chromatids exchange genetic information via homologous recombination. This shuffles genetic information and increases genetic variation. Avg. crossing over events = 2-3/homologous pair. 15 LO 4 Independent Assortment Independent assortment represents the different ways chromosomes line up at the metaphase plate. This leads to different combinations of genetic material in the gametes. Note the figure is only showing 2 of 4 gametes and crossing-over is not represented. 16 LO 4 Nondisjunction in Meiosis I ↳ [Homologous chromosomes fail to separate in Meiosis I This leads to production of aneuploid (cells with an incorrect # of chromo) gametes. Why is this a problem? What would the gametes look like if Nondisjunction occurred in Meiosis II? 17 LO 5 · Class Question : draw · out What would happen if Nondisjunction occurs In Meiosis# So So ↓ duplication & · d  Vondisjuncta nondisjunctia ·aneuploidyo Which of the following statements is FALSE? a. Asexual reproduction typically gives rise to offspring that are genetically identical. not used for reproduction ⑧ ↑ b. Mutations in somatic cells are passed on to individuals of the next generation. It would - Gomete c. Sexual reproduction allows for a wide variety of gene combinations. d. Gametes are specialized sex cells. 18 Homologous chromosomes undergo crossing over during: a. anaphase I. O b. prophase I. c. anaphase II. d. telophase II. e. prophase II. 19 Which of the following statements about the benefits of sexual reproduction is FALSE? ⑧a. Sexual reproduction permits enhanced survival because the gametes that carry alleles enhancing survival in harsh environments are used preferentially t true its random) during fertilization. - b. Unicellular organisms that can undergo sexual reproduction have an increased ability to adapt to harsh environments. c. Sexual reproduction reshuffles genes, which is thought to help species survive in novel or varying environments. d. Sexual reproduction can speed the elimination of deleterious alleles. 20 Overview of the Cell Cycle Control System 21  If yes, then The Cell Cycle G = growth (or gap) S = DNA synthesis M = mitosis Checkpoints = G1/S, G2/M, and M. G0 is a quiescent phase. G0 22 LO 6 If yes, then Flow cytometry can be used to determine the number or proportion of cells in different stages of the cell cycle How many cells are fluorescent A fluorescent DNA binding dye is added to cells. How much is fluorescence Image from: https://www.testing.com/flow-cytometry/ 23 LO 6 is in each cell  Analyze the figure What stage(s) of the cell cycle do you expect cells to have 1x DNA content? 2x DNA? In between 1-2x DNA? Why is peak B smaller than peak A? If the peaks shifted so that more cells were in peak B, what may that tell you about the cell population?= I content: G #-smaller ble theres a checkpoint t not all calls 2 conte will be to enter mitosis were in ready G, make , so not all alls the Un blur SorM : it to next ? 24 LO 6 Which of the following is responsible for phosphorylating - proteins? A) Phosphatase B) Phosphomutase ⑳ C) D) Kinase phosphorylates Regulase > - 25 Cell Cycle Regulation 26 Cdk 🖤 cyclins Cyclin dependent protein kinases (Cdk) are made in similar amounts throughout the cell cycle. Cyclins accumulate only at certain times during the cell cycle. Cdk DEPEND on cyclins to phosphorylate other proteins. 27 LO 6 & 7 Cyclins activate Cdk. Cdk then phosphorylate other proteins promoting progression through the cell cycle. 28 LO 6 & 7 M Cyclin example - M-Cyclin concentration changes throughout the cell cycle, thereby modulating M-Cdk activity. 29 LO 6 & 7  Different cyclins regulate specific stages of the cell cycle. Why? 30 LO 6 & 7  Cell Cycle Regulation Means it inhibits Cdk/cyclin location denotes when it acts during the cell cycle. Activated cdk/cyclin promotes cell cycle progression LO 6 & 7 31 Activity 2 - In your group, review the following 4 slides and explore the mechanisms that control Cdk activity. Explain why it is important to have multiple ways to modulate the activity of Cdk’s. LO 6 & 7 32 Following Slides Regulaty CDK Activity : The activity of Cdk complexes are tightly controlled By cyclin ubiquitilylation... 33 LO 6 & 7 The activity of Cdk complexes are tightly controlled By phosphorylation and dephosphorylation... LO 6 & 7 34 The activity of Cdk complexes are tightly controlled By inhibitors... LO 6 & 7 35  The activity of cdk + cell cycle checkpoints prevent the cell from progressing through the cell cycle Predict what would happen if the regulatory mechanisms on the previous slides malfunctioned. What would specifically happen to the cells? LO 6, 7, & 8 36  The activity of Cdk complexes are tightly controlled Watch Movie 18.1 - Cdk2 Outside of class: For additional support on the cell cycle and cell cycle regulation see https://www.khanacademy.org/science/ap-biology/cell-communication-and-cell-cyc le/regulation-of-cell-cycle/a/cell-cycle-regulators Or the HHMI Biointeractive activity https://media.hhmi.org/biointeractive/click/cellcycle/ LO 6, 7, & 8 37  Debrief. Explore the mechanisms that control Cdk activity. Explain why it is important to have multiple ways to modulate the activity of Cdk’s. LO 6, 7, & 8 38 A mutant yeast strain stops proliferating when shifted from 25°C to 37°C. When these cells are analyzed at the two different temperatures, using a machine that sorts cells according to the amount of DNA they contain, the graphs shown are obtained. Which of the following would NOT explain the results with the mutant? A. inability to initiate DNA replication ① B. inability to begin M phase C. inability to activate proteins needed to enter S phase D. inappropriate production of a signal that causes the cells 39 to remain in G1 G1 phase regulation 40 Transition from G1/S is the most tightly regulated Major crossroads for cell to decide what to do. Growth factors, nutrient availability and space determine what happens At the completion of a cell cycle the cell needs to: ○ Eliminate existing cyclins from previous cycle - RESET ○ Block synthesis of new cyclins ○ Activate Cdk inhibitors ○ Await mitogen stimulation LO 6 and 7 41 Rb regulates the G1/S phase transition Rb is a negative regulator of the cell cycle. It binds E2F (a transcription No Transcription factor) that promotes of genes transcription of proteins needed for entry into S phase. required for S E2F phase When Rb is active, the cell can not progress into S phase. So, Rb is a transcriptional repressor LO 6 & 7 42  LO 6, 7, & 8 Rb regulates the G1/S phase transition When mitogens are present, they activate G1-Cdk and G1/S Cdk. Activated Cdks phosphorylate Rb Phospho-Rb releases E2F E2F binds DNA and promotes transcription of S phase genes Cell enters S phase E2F E2F What would happen if Rb were constantly inactivated? 43  If Rb (a tumor suppressor) is mutated, the cell cycle can become dysregulated, leading to development of Retinoblastoma, a cancer of the retina. 44 LO 6, 7, & 8 p53 is also a tumor suppressor that regulates the cell cycle Use the figures below to explain to your neighbor how p53 and p21 function in the cell cycle LO 6, 7, & 8 45 How is p53 regulating the cell cycle? How is p21 regulating the cell cycle? LO 6 & 7 46 What would happen if p53 was mutated? LO 8 47 Image accessed from: https://www.nature.com/articles/s41418-018-0246-9 The p53 tumor suppressor is frequently mutated in cancer LO 8 Image accessed from: https://www.mdpi.com/1422-0067/20/24/6241/htm 48 S Phase regulation 49 Regulating DNA synthesis ORC remains associated with the Ori Cdc6 rises in G1 - helps load helicase S-Cdk activates helicase and assembles proteins at the replication fork S-Cdk also phosphorylates cdc6 (not shown) to prevent reassembly of replication complex 50 M phase regulation 51 Cdc25 activation drives cells into mitosis by dephosphorylating M-Cdk Wee1 adds these inhibitory phosphates. LO 6 & 7 52  Cohesins vs. Condensins Cohesins keep sister chromatids together until anaphase. Condensins allow chromosomes to condense during prophase. LO 2, 6 & 7 53  LO 2, 6 & 7 How do chromatids separate at Anaphase? Separase cleaves the cohesins that hold sister chromatids together Separase is normally bound by securin Active APC/C tags securin with ubiquitin, targeting it for degradation This frees separase Watch movie 18.7 - the kinetochore 54 Microtubules and actin microfilaments are important for the mitotic spindle and cytokinesis in animal cells Can you identify the following: sister chromatids, kinetochores, centromeres, centrosomes, centrioles, kinetochore microtubules and non-kinetochore microtubules? 55 LO 2 Thank you! Have a Happy Thanksgiving!! What questions do you have? How can I help clarify? 56