Apoptosis and Cell Cycle Quiz
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Questions and Answers

What is the main function of apoptosis in cellular biology?

  • To create energy for cell function
  • To promote cell regeneration
  • To initiate inflammation
  • To eliminate unwanted cells (correct)
  • Which pathway of apoptosis is initiated by the activation of cell surface death receptors?

  • Regulatory pathway
  • Intrinsic pathway
  • Extrinsic pathway (correct)
  • Caspase pathway
  • What role do initiator caspases play in the apoptosis process?

  • They inhibit apoptosis
  • They directly cleave DNA
  • They stabilize mitochondria
  • They activate execution caspases (correct)
  • What critical proteins are released from mitochondria during the intrinsic pathway of apoptosis?

    <p>Cytochrome c</p> Signup and view all the answers

    Which of the following statements about caspases is correct?

    <p>Caspases have a cysteine in their active site</p> Signup and view all the answers

    What is a consequence of inappropriate levels of apoptosis?

    <p>Contributing to disease</p> Signup and view all the answers

    During DNA fragmentation in apoptosis, which enzyme is involved in cleaving the DNA?

    <p>CAD</p> Signup and view all the answers

    What is the effect of extracellular survival factors on apoptosis?

    <p>They prevent apoptosis</p> Signup and view all the answers

    What role does positive feedback play in the activation of m-cdk?

    <p>It leads to the activation of cdc25.</p> Signup and view all the answers

    What is the key regulatory event in the late M phase?

    <p>The inactivation of cdks.</p> Signup and view all the answers

    How does the Anaphase-promoting complex/cyclosome (Apc/c) function?

    <p>It assembles polyubiquitin chains on target proteins.</p> Signup and view all the answers

    What happens to cdc25 and Wee1 when m-cdk is activated?

    <p>Cdc25 is activated and Wee1 is inhibited.</p> Signup and view all the answers

    What triggers DNA replication in the cell cycle?

    <p>S-cdk initiation.</p> Signup and view all the answers

    What effect does the stable G1 phase have on the cell?

    <p>The cell grows and monitors its environment.</p> Signup and view all the answers

    What triggers the separation of sister chromatids during mitosis?

    <p>Ubiquitylation of securin</p> Signup and view all the answers

    What is the role of the spindle assembly checkpoint in mitosis?

    <p>To block the transition from metaphase to anaphase</p> Signup and view all the answers

    Which structure holds sister chromatids together during cell division?

    <p>Cohesins.</p> Signup and view all the answers

    Which molecule is cleaved to allow sister chromatids to separate?

    <p>Scc1</p> Signup and view all the answers

    How is m-cdk inactivated as cells prepare to enter a new cell cycle?

    <p>Through degradation of m-cyclin.</p> Signup and view all the answers

    What component of the mitotic spindle helps determine the plane of cell division?

    <p>Microtubules</p> Signup and view all the answers

    How does rhoA influence the process of cytokinesis?

    <p>By triggering assembly and contraction of the contractile ring</p> Signup and view all the answers

    What happens immediately after the last sister chromatid pair becomes bi-oriented on the spindle?

    <p>Destruction of securin begins</p> Signup and view all the answers

    During which phase of mitosis do chromosomes segregate into daughter cells?

    <p>Anaphase</p> Signup and view all the answers

    Which of the following statements about cytokinesis is true?

    <p>Mitosis can occur without cytokinesis.</p> Signup and view all the answers

    What event triggers the start of the cell cycle?

    <p>The initiation of DNA replication</p> Signup and view all the answers

    Which phase do cells have double the DNA content due to DNA replication?

    <p>G2 phase</p> Signup and view all the answers

    What occurs during the G2/M transition in the cell cycle?

    <p>Cells trigger mitosis</p> Signup and view all the answers

    Which protein complex initiates the transition from metaphase to anaphase?

    <p>APC/C</p> Signup and view all the answers

    What function do cyclins serve in the cell cycle control system?

    <p>Activate the necessary kinases</p> Signup and view all the answers

    What is the role of the Cdk inhibitor protein (cki)?

    <p>Distort the active site of Cdk</p> Signup and view all the answers

    How is the cyclin-Cdk complex activated?

    <p>By the removal of inhibitory phosphates</p> Signup and view all the answers

    What happens to the Cdk proteins during the cell cycle?

    <p>Their levels remain constant</p> Signup and view all the answers

    What triggers the conformational change in Apaf1 leading to apoptosome formation?

    <p>Binding of cictrhrome C</p> Signup and view all the answers

    What is the role of Bak in the process of apoptosis?

    <p>It oligomerizes in the outer membrane to induce MOMP.</p> Signup and view all the answers

    How do BH3-only proteins like Bad contribute to apoptosis?

    <p>By inhibiting anti-apoptotic Bcl2 proteins.</p> Signup and view all the answers

    What is MOMP and its significance in apoptosis?

    <p>Mitochondrial outer membrane permeabilization allowing protein release into the cytosol.</p> Signup and view all the answers

    What role do anti-apoptotic Bcl2 family proteins play?

    <p>They inhibit pro-apoptotic proteins to prevent apoptosis.</p> Signup and view all the answers

    Which statement correctly describes IAP proteins?

    <p>They prevent the activation of caspases during apoptosis.</p> Signup and view all the answers

    What is the primary function of cytochrome C in apoptosis?

    <p>To activate the apoptosome complex.</p> Signup and view all the answers

    What is the expected outcome when pro-apoptotic factors are activated?

    <p>Induction of apoptosis via caspase activation.</p> Signup and view all the answers

    What role does the protein m o m p play in relation to apoptosis?

    <p>Releases anti-IAP proteins to mitigate caspase activity.</p> Signup and view all the answers

    Which protein is responsible for phosphorylating and inactivating bad in the apoptotic pathway?

    <p>Akt</p> Signup and view all the answers

    Why do some nerve cells undergo apoptosis during development?

    <p>Because they receive insufficient survival factors.</p> Signup and view all the answers

    What is the significance of phosphatidylserine in the context of apoptosis?

    <p>It serves as an 'eat me' signal for phagocytic cells.</p> Signup and view all the answers

    How do extracellular survival factors generally inhibit apoptosis?

    <p>By stimulating the transcription of anti-apoptotic proteins.</p> Signup and view all the answers

    What happens to flippase during the apoptotic process?

    <p>It is inactivated, allowing phosphatidylserine to move outward.</p> Signup and view all the answers

    What can happen if apoptosis is either excessive or insufficient?

    <p>It can contribute to various diseases.</p> Signup and view all the answers

    What is the function of scramblase in the apoptosis process?

    <p>To randomly transfer lipids between membrane leaflets.</p> Signup and view all the answers

    Study Notes

    Cell Cycle

    • Eukaryotic cells divide to produce genetically identical daughter cells
    • Cell cycle has several phases involved in chromosomal duplication and segregation
    • Major chromosomal events of the cell cycle occur in S phase (duplication) and M phase (segregation).
    • Interphase includes G1, S, and G2 phases
    • G1 phase: cell growth and normal metabolic roles
    • S phase: replication of DNA
    • G2 phase: cell growth and preparation for mitosis

    Eukaryotic Cell Division

    • M phase typically occupies a small fraction of the cell cycle
    • Interphase includes S phase and gap phases
    • Stages of mitosis:
      • Prophase: chromosomes condense
      • Prometaphase: spindle microtubules attach to chromosomes
      • Metaphase: chromosomes align at cell equator
      • Anaphase: sister chromatids separate
      • Telophase: chromosomes arrive at opposite ends

    Cytokinesis

    • Division of the cytoplasm, forming 2 cells
    • Two major regulatory steps in mitosis involve:
      • M-cdk and other protein kinase drive entry into mitosis
      • Apc/c triggers the destruction of securin, initiating sister chromatid separation

    Cell Cycle Control

    • Cell cycle control at three major regulatory transitions:
      • Start, when the cell commits to cell cycle entry and DNA replication
      • G2/M transition, when the cell triggers mitosis
      • Metaphase to anaphase transition, which triggers sister chromatid separation
    • Hundreds of cdk substrates are phosphorylated in a defined order
    • Not well understood how the correct order of phosphorylation is achieved
    • Positive feedback generates the switch-like behavior of cell-cycle transitions

    Cell Cycle Control System

    • Depends on cyclically activated cyclin-dependent protein kinases (cdks)
    • Cyclins undergo a cycle of synthesis and degradation in each cell cycle
    • Cyclical changes in cyclin protein levels result in cyclic assembly and activation of cyclin–cdk complexes
    • Concentrations of three major cyclin types oscillate during the cell cycle
    • A separate regulatory protein complex, the APC/C, initiates the metaphase to anaphase transition
    • Phosphorylation of Cdk2 (by CAK) activates the enzyme
    • Cdk activity is regulated by inhibitory phosphorylation (Wee1) and activation (Cdc25 phosphatase)

    Regulation of Cdk Activity

    • The active cyclin-cdks are off when kinase Wee1 phosphorylates two sites above the active site.
    • Removal of these phosphates by phosphatase Cdc25 activates the complex
    • CAK adds the activating phosphate
    • cdk inhibitors (CKIs) can inhibit Cdk activity
    • Protein phosphatases reverse the effects of cdks

    Mitosis

    • Major steps summarized:
      • Prophase: chromosomes condense
      • Prometaphase: spindle microtubules attach to chromosomes
      • Metaphase: chromosomes align at cell equator
      • Anaphase: sister chromatids separate
      • Telophase: chromosomes arrive at opposite ends
      • Cytokinesis: division of the cytoplasm

    Cell Cycle and DNA Replication

    • S phase: DNA replication occurs only once per cell cycle
    • Chromosome duplication requires duplication of chromatin structure
    • Cohesins hold sister chromatids together.

    Meiosis

    • Special type of nuclear division that differs from mitosis
    • In animals, meiosis occurs in the gonads
    • Results in four genetically unique daughter cells (gametes) each with just one set of chromosomes
    • Duplicated homologs pair during meiotic prophase
    • Crossing over holds bivalents together, and contributes to genetic variation

    Mitosis-Telophase

    • Chromosomes are packaged in daughter nuclei
    • Actin and myosin II in the contractile ring guide the process of cytokinesis

    Cytokinesis

    • Microtubules of the mitotic spindle determine the plane of animal cell division
    • This ensures that the cleavage plane is between the two daughter nuclei

    Control of Cell Division and Growth

    • Mitogens stimulate cell division, primarily by triggering a wave of G1/S-cdk activity
    • Growth factors stimulate cell growth by promoting protein synthesis
    • Survival factors promote cell survival by suppressing apoptosis
    • Many human cells have a limitations on the number of times they can divide

    DNA Damage

    • DNA damage leads to accumulation of active p53 protein, arresting the cell in G1 until DNA repair is required

    Apoptosis

    • Apoptosis eliminates unwanted cells
    • Depends on an intracellular proteolytic cascade mediated by caspases
    • Extrinsic pathway: activation of cell surface death receptors
    • Intrinsic pathway: depends on proteins released from mitochondria
    • Inhibitors of apoptosis (IAPs) help control caspase activation
    • Caspases are proteases that cleave targets after aspartate residue.
    • Initiator caspases activate execution caspases which lead to controlled apoptotic death.

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    Related Documents

    Cell Cycle - Exam 4 PDF

    Description

    Test your knowledge on the mechanisms of apoptosis and the cell cycle. This quiz covers key processes like initiator caspases, mitochondrial proteins, and the regulation of cell division. Perfect for students studying cellular biology at an advanced level.

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