Cell Cycle Checkpoints and Regulation Quiz
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Questions and Answers

What is the role of Cdk inhibitory proteins (CKIs) in the cell cycle?

  • Stimulating chromosome attachment to the mitotic spindle
  • Inactivating cyclin-Cdk complexes (correct)
  • Promoting progression through G2 phase
  • Activating cyclin-Cdk complexes

    • Which condition would prevent entry into the M phase of the cell cycle?

  • DNA replication is not complete (correct)
  • Abnormal cell size
  • Presence of DNA damage
  • Absence of growth factors

    • What happens at the end of mitosis regarding the M-cyclins?

  • They activate checkpoints for further cell division
  • They are duplicated for future use
  • They are targeted for destruction by APC/C (correct)
  • They initiate cytokinesis

    • What is the primary role of Cdk inhibitory proteins (CKIs) early in the cell cycle?

    <p>Regulating G1/S and S-Cdks activities</p> Signup and view all the answers

    What condition would prevent progression through G1 phase of the cell cycle?

    <p>Presence of DNA damage</p> Signup and view all the answers

    What is required for the completion of M phase in the cell cycle, including telophase and cytokinesis?

    <p>Phosphorylation of Cdk targets by phosphatases</p> Signup and view all the answers

    What are checkpoints in the cell cycle?

    <p>Points where the cell cycle stops until conditions are suitable for the cell to proceed</p> Signup and view all the answers

    Which transition is considered the ratelimiting step of the cell cycle for most cells?

    <p>G1/S transition</p> Signup and view all the answers

    What regulates cell cycle checkpoints?

    <p>Factors within the cell and messages from outside the cell</p> Signup and view all the answers

    What happens if a cell detects a problem at a checkpoint?

    <p>It blocks progression beyond that checkpoint</p> Signup and view all the answers

    Which checkpoint is also known as the 'Start transition'?

    <p>G1/S checkpoint</p> Signup and view all the answers

    What role do specific signals play at cell cycle checkpoints?

    <p>They are necessary for a cell to pass through the checkpoints</p> Signup and view all the answers

    Which CKI inhibits the G1/S-cdk complex, S-cdk complex, and M-cdk complex?

    <p>p21</p> Signup and view all the answers

    Which of the following statements about p53 is not true?

    <p>p53 is found at higher levels in unstressed cells due to its degradation by Mdm2.</p> Signup and view all the answers

    Which of the following complexes is not involved in stimulating chromosome duplication or early mitotic events?

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

    Which of the following statements about RB (Retinoblastoma protein) is true?

    <p>RB is hypo- or hyperphosphorylated, depending on its activity.</p> Signup and view all the answers

    Which CKI inhibits the G1-cdk complex (Cyclin D-cdk4 & Cyclin D-cdk6)?

    <p>p16</p> Signup and view all the answers

    Which of the following statements about the M-Cdk complex (Cyclin B-cdk1) is false?

    <p>It is involved in chromosome duplication.</p> Signup and view all the answers

    What is the primary function of cyclins in the cell cycle?

    <p>To activate cyclin-dependent kinases (Cdks) and direct them to specific target proteins</p> Signup and view all the answers

    What is the role of cyclin-activating kinase (CAK) in the regulation of the cell cycle?

    <p>It is required for the full activation of cyclin-Cdk complexes</p> Signup and view all the answers

    How do cyclin-Cdk complexes regulate different cellular processes during the cell cycle?

    <p>By phosphorylating different target proteins that become accessible at specific cell cycle phases</p> Signup and view all the answers

    What is the role of the anaphase-promoting complex (APC/C) in the cell cycle?

    <p>It stimulates the proteolytic destruction of specific regulatory proteins during the metaphase-to-anaphase transition</p> Signup and view all the answers

    What is the mechanism by which the APC/C targets proteins for degradation?

    <p>It polyubiquitinates specific target proteins, marking them for destruction in proteasomes</p> Signup and view all the answers

    Which of the following statements about cyclins and cyclin-dependent kinases (Cdks) is correct?

    <p>Cyclins are the regulatory subunits of the cyclin-Cdk complexes, and they direct Cdks to specific target proteins</p> Signup and view all the answers

    What is the primary function of DNA ligase during DNA replication?

    <p>To join the 3' end of the new DNA fragment with the 5' end of the previous fragment</p> Signup and view all the answers

    What is the primary cause of supercoiling during DNA replication?

    <p>The unwinding of the DNA double helix ahead of the replication fork</p> Signup and view all the answers

    Which enzyme is responsible for relieving the superhelical tension caused by DNA unwinding during replication?

    <p>DNA topoisomerase</p> Signup and view all the answers

    What is the primary function of histone chaperones during DNA replication in eukaryotes?

    <p>To assist in the formation of histone octamers and nucleosomes</p> Signup and view all the answers

    During which phase of the cell cycle does histone synthesis primarily occur in eukaryotes?

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

    Which of the following statements accurately describes the role of DNA topoisomerase during DNA replication?

    <p>It breaks and rejoins the phosphodiester bonds in the DNA strand, allowing the DNA to unwind and relieve torsional stress caused by supercoiling.</p> Signup and view all the answers

    Which cyclin-Cdk complex is responsible for stimulating chromosome duplication during the S phase of the cell cycle?

    <p>Cyclin A-Cdk1/2 complex</p> Signup and view all the answers

    Which cyclin-Cdk complex is primarily responsible for triggering progression through the G1/S transition, also known as the 'Start transition'?

    <p>Cyclin E-Cdk2 complex</p> Signup and view all the answers

    Which cyclin-Cdk complex is responsible for stimulating entry into the M phase of the cell cycle at the G2/M transition?

    <p>Cyclin B-Cdk1 complex</p> Signup and view all the answers

    Which of the following statements about the role of the Cyclin D-Cdk4/6 complex in the cell cycle is correct?

    <p>The Cyclin D-Cdk4/6 complex is needed for progression through the G1/S transition.</p> Signup and view all the answers

    Which of the following statements about the role of the Cyclin A-Cdk1/2 complex in the cell cycle is correct?

    <p>The Cyclin A-Cdk1/2 complex is responsible for stimulating chromosome duplication during the S phase.</p> Signup and view all the answers

    Which of the following statements about the role of the Cyclin B-Cdk1 complex in the cell cycle is false?

    <p>The Cyclin B-Cdk1 complex is needed for progression through the G1/S transition.</p> Signup and view all the answers

    How does Akt promote cell cycle progression?

    <p>Activating Cyclin A</p> Signup and view all the answers

    Which of the following is not a role of Akt in the cell cycle?

    <p>Inactivation of Cyclin A</p> Signup and view all the answers

    What is the main function of p21 and p27 in relation to the cell cycle?

    <p>Inhibit Cyclin-Cdk complexes</p> Signup and view all the answers

    Which enzyme regulates the checkpoint that is not regulated by cyclin-Cdk complexes?

    <p>p16</p> Signup and view all the answers

    How do p16, p21, and p27 affect the cell cycle?

    <p>Inhibit cell cycle progression</p> Signup and view all the answers

    What is the function of RB in stopping the cell cycle?

    <p>Binding E2F transcription factors</p> Signup and view all the answers

    Which phase of the cell cycle is characterized by the synthesis of enzymes, proteins, and ATP, as well as continued cell growth?

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

    During which phase does DNA replication occur, creating two identical daughter genomes?

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

    The duration of the M phase, where the cell undergoes mitosis and cytokinesis, typically lasts how long in a mammalian cell with a 16-hour cycle?

    <p>1-2 hours</p> Signup and view all the answers

    Which phase is considered the rate-limiting step of the cell cycle for most cells?

    <p>G1 phase</p> Signup and view all the answers

    In which phase do growth factors play a crucial role in determining whether a cell proceeds with division or enters a quiescent state?

    <p>G1 phase</p> Signup and view all the answers

    Which phase is typically the shortest in duration for a mammalian cell with a 16-hour cycle?

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

    What is the primary mechanism by which DNA polymerase ensures high fidelity during DNA replication?

    <p>DNA polymerase has a proofreading mechanism that can detect and correct errors before the next nucleotide is added</p> Signup and view all the answers

    What is the primary reason that the error rate during DNA replication is much lower than the error rate during transcription (RNA polymerase)?

    <p>DNA replication has additional proofreading mechanisms that transcription lacks</p> Signup and view all the answers

    What is the primary function of the 3'-to-5' exonuclease activity of DNA polymerase during proofreading?

    <p>It removes incorrectly added nucleotides from the 3' end of the DNA strand</p> Signup and view all the answers

    Which of the following is NOT a proofreading mechanism used by DNA polymerase during DNA replication?

    <p>A separate mismatch repair system corrects errors made during replication</p> Signup and view all the answers

    What is the primary reason that the error rate during DNA replication is approximately 1 mistake per $10^{10}$ nucleotides, which is much lower than the error rate during transcription (RNA polymerase)?

    <p>DNA replication has more proofreading mechanisms than transcription</p> Signup and view all the answers

    What is the primary function of the strand-directed mismatch repair system mentioned in the text?

    <p>It is not a proofreading mechanism used by DNA polymerase during replication</p> Signup and view all the answers

    What is the role of DNA ligase in DNA replication?

    <p>Joins the 3’ end of a new DNA fragment with the 5’ end of the previous fragment</p> Signup and view all the answers

    How does DNA topoisomerase contribute to DNA replication?

    <p>Relieves supercoiling tension</p> Signup and view all the answers

    What is a key function of histone chaperones during DNA replication?

    <p>Packaging newly replicated DNA into nucleosomes</p> Signup and view all the answers

    Which enzyme is responsible for relieving supercoiling tension during DNA replication?

    <p>DNA topoisomerase</p> Signup and view all the answers

    In DNA replication, what is the main task of DNA topoisomerase?

    <p>Managing supercoiling tension</p> Signup and view all the answers

    During which phase of the cell cycle is histone synthesis primarily carried out in eukaryotes?

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

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