Cell-Cycle Control System and SCF Ubiquitin Ligase Quiz
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Questions and Answers

What is the first visible change of cytokinesis in an animal cell?

  • Division of the cell in two
  • Assembly of actin filaments
  • Formation of a contractile ring
  • Appearance of a cleavage furrow (correct)

    • Which structure is responsible for the division of an animal cell during cytokinesis?

  • Myosin II filaments
  • Contractile ring (correct)
  • Actin filaments
  • RhoA protein

    • What triggers the assembly and contraction of the contractile ring during cytokinesis?

  • Activation of RhoA by RhoGEF (correct)
  • Division of the cell in two
  • Assembly of actin filaments
  • Release of GDP by Myosin II

    • What is the function of RhoA in cytokinesis?

    <p>Control of contractile ring assembly</p> Signup and view all the answers

    Which protein is involved in the formation of the contractile ring in animal cells?

    <p>Actin filaments</p> Signup and view all the answers

    What is the role of a guanine nucleotide exchange factor (RhoGEF) during cytokinesis?

    <p>Stimulation of RhoA activation</p> Signup and view all the answers

    Which process occurs just beneath the plasma membrane during anaphase?

    <p>Assembly of the contractile ring</p> Signup and view all the answers

    What is the main structure underlying cytokinesis in an animal cell?

    <p>Contractile ring</p> Signup and view all the answers

    Where does the contractile ring assemble during cytokinesis?

    <p>Just beneath the plasma membrane</p> Signup and view all the answers

    What is the function of RhoA during cytokinesis?

    <p>Activating the contractile ring assembly and function</p> Signup and view all the answers

    Which protein is essential for the contraction of the contractile ring during animal cell cytokinesis?

    <p>Myosin II</p> Signup and view all the answers

    What triggers the formation of the cleavage furrow during cytokinesis in animal cells?

    <p>Contractile ring</p> Signup and view all the answers

    Which factor stimulates the release of GDP and binding of GTP to RhoA during cytokinesis?

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

    What is the role of actin filaments in the contractile ring during cytokinesis?

    <p>Cell division contractility</p> Signup and view all the answers

    During which cell cycle phase does the contractile ring assemble in preparation for cell division?

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

    What is the role of cyclins in the activity of Cdks?

    <p>Binding to Cdks to activate them</p> Signup and view all the answers

    Which class of cyclins helps govern the activities of G1/S-cyclins in late G1?

    <p>G1-cyclins</p> Signup and view all the answers

    When do M-cyclin levels decrease?

    <p>Mid-mitosis</p> Signup and view all the answers

    Which type of cyclin stimulates entry into mitosis at the G2/M transition?

    <p>M-cyclins</p> Signup and view all the answers

    What happens to S-cyclin levels until mitosis begins?

    <p>They stay elevated until mitosis</p> Signup and view all the answers

    What is the role of securin destruction at the end of metaphase?

    <p>Leads to the separation of sister chromatids</p> Signup and view all the answers

    What is the consequence of APC/C targeting S- and Mcyclins for destruction?

    <p>Inactivation of Cdk activity in anaphase</p> Signup and view all the answers

    How does APC/C activation occur?

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

    What is the significance of M-Cdk promoting Cdc20–APC/C activity?

    <p>Creates a negative feedback loop for cyclin destruction</p> Signup and view all the answers

    What occurs when Cdk becomes inactivated in the cell cycle?

    <p>Activation of phosphatases for Cdk phosphorylation</p> Signup and view all the answers

    What is the role of the Anaphase-Promoting Complex/Cyclosome (APC/C) in late M phase events?

    <p>Facilitates the destruction of cyclins</p> Signup and view all the answers

    What is the function of Cdk-activating kinase (CAK) during M-Cdk activation?

    <p>Phosphorylates Cdk at an activating site</p> Signup and view all the answers

    What triggers the activation of the 'stockpile' of M-Cdk at the end of G2 phase?

    <p>Suppression of inhibitory phosphates by Cdc25</p> Signup and view all the answers

    What is the role of protein phosphatase Cdc25 in M-Cdk activation?

    <p>Removes inhibitory phosphates from M-Cdk</p> Signup and view all the answers

    How does positive feedback loops contribute to M-Cdk activation during mitosis?

    <p>Inhibits its own inhibitor Wee1 and activates its activator Cdc25</p> Signup and view all the answers

    What is the role of cyclin in the activation of Cdk?

    <p>Directs Cdk to specific target proteins</p> Signup and view all the answers

    Which type of phosphorylation inhibits the activity of a cyclin–Cdk complex?

    <p>Phosphorylation by Wee1</p> Signup and view all the answers

    What structural change occurs in the Cdk protein upon binding with cyclin?

    <p>Loop moves away from the active site, partially activating the enzyme</p> Signup and view all the answers

    Which protein phosphorylates an amino acid near the entrance of the Cdk active site for full activation of the cyclin–Cdk complex?

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

    What effect does dephosphorylation by Cdc25 have on a cyclin–Cdk complex?

    <p>Increases Cdk activity</p> Signup and view all the answers

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