60 Questions
What is the role of Cdk inhibitory proteins (CKIs) in the cell cycle?
Inactivating cyclin-Cdk complexes
Which condition would prevent entry into the M phase of the cell cycle?
DNA replication is not complete
What happens at the end of mitosis regarding the M-cyclins?
They are targeted for destruction by APC/C
What is the primary role of Cdk inhibitory proteins (CKIs) early in the cell cycle?
Regulating G1/S and S-Cdks activities
What condition would prevent progression through G1 phase of the cell cycle?
Presence of DNA damage
What is required for the completion of M phase in the cell cycle, including telophase and cytokinesis?
Phosphorylation of Cdk targets by phosphatases
What are checkpoints in the cell cycle?
Points where the cell cycle stops until conditions are suitable for the cell to proceed
Which transition is considered the ratelimiting step of the cell cycle for most cells?
G1/S transition
What regulates cell cycle checkpoints?
Factors within the cell and messages from outside the cell
What happens if a cell detects a problem at a checkpoint?
It blocks progression beyond that checkpoint
Which checkpoint is also known as the 'Start transition'?
G1/S checkpoint
What role do specific signals play at cell cycle checkpoints?
They are necessary for a cell to pass through the checkpoints
Which CKI inhibits the G1/S-cdk complex, S-cdk complex, and M-cdk complex?
p21
Which of the following statements about p53 is not true?
p53 is found at higher levels in unstressed cells due to its degradation by Mdm2.
Which of the following complexes is not involved in stimulating chromosome duplication or early mitotic events?
G1-Cdk complex
Which of the following statements about RB (Retinoblastoma protein) is true?
RB is hypo- or hyperphosphorylated, depending on its activity.
Which CKI inhibits the G1-cdk complex (Cyclin D-cdk4 & Cyclin D-cdk6)?
p16
Which of the following statements about the M-Cdk complex (Cyclin B-cdk1) is false?
It is involved in chromosome duplication.
What is the primary function of cyclins in the cell cycle?
To activate cyclin-dependent kinases (Cdks) and direct them to specific target proteins
What is the role of cyclin-activating kinase (CAK) in the regulation of the cell cycle?
It is required for the full activation of cyclin-Cdk complexes
How do cyclin-Cdk complexes regulate different cellular processes during the cell cycle?
By phosphorylating different target proteins that become accessible at specific cell cycle phases
What is the role of the anaphase-promoting complex (APC/C) in the cell cycle?
It stimulates the proteolytic destruction of specific regulatory proteins during the metaphase-to-anaphase transition
What is the mechanism by which the APC/C targets proteins for degradation?
It polyubiquitinates specific target proteins, marking them for destruction in proteasomes
Which of the following statements about cyclins and cyclin-dependent kinases (Cdks) is correct?
Cyclins are the regulatory subunits of the cyclin-Cdk complexes, and they direct Cdks to specific target proteins
What is the primary function of DNA ligase during DNA replication?
To join the 3' end of the new DNA fragment with the 5' end of the previous fragment
What is the primary cause of supercoiling during DNA replication?
The unwinding of the DNA double helix ahead of the replication fork
Which enzyme is responsible for relieving the superhelical tension caused by DNA unwinding during replication?
DNA topoisomerase
What is the primary function of histone chaperones during DNA replication in eukaryotes?
To assist in the formation of histone octamers and nucleosomes
During which phase of the cell cycle does histone synthesis primarily occur in eukaryotes?
S phase
Which of the following statements accurately describes the role of DNA topoisomerase during DNA replication?
It breaks and rejoins the phosphodiester bonds in the DNA strand, allowing the DNA to unwind and relieve torsional stress caused by supercoiling.
Which cyclin-Cdk complex is responsible for stimulating chromosome duplication during the S phase of the cell cycle?
Cyclin A-Cdk1/2 complex
Which cyclin-Cdk complex is primarily responsible for triggering progression through the G1/S transition, also known as the 'Start transition'?
Cyclin E-Cdk2 complex
Which cyclin-Cdk complex is responsible for stimulating entry into the M phase of the cell cycle at the G2/M transition?
Cyclin B-Cdk1 complex
Which of the following statements about the role of the Cyclin D-Cdk4/6 complex in the cell cycle is correct?
The Cyclin D-Cdk4/6 complex is needed for progression through the G1/S transition.
Which of the following statements about the role of the Cyclin A-Cdk1/2 complex in the cell cycle is correct?
The Cyclin A-Cdk1/2 complex is responsible for stimulating chromosome duplication during the S phase.
Which of the following statements about the role of the Cyclin B-Cdk1 complex in the cell cycle is false?
The Cyclin B-Cdk1 complex is needed for progression through the G1/S transition.
How does Akt promote cell cycle progression?
Activating Cyclin A
Which of the following is not a role of Akt in the cell cycle?
Inactivation of Cyclin A
What is the main function of p21 and p27 in relation to the cell cycle?
Inhibit Cyclin-Cdk complexes
Which enzyme regulates the checkpoint that is not regulated by cyclin-Cdk complexes?
p16
How do p16, p21, and p27 affect the cell cycle?
Inhibit cell cycle progression
What is the function of RB in stopping the cell cycle?
Binding E2F transcription factors
Which phase of the cell cycle is characterized by the synthesis of enzymes, proteins, and ATP, as well as continued cell growth?
G2 phase
During which phase does DNA replication occur, creating two identical daughter genomes?
S phase
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?
1-2 hours
Which phase is considered the rate-limiting step of the cell cycle for most cells?
G1 phase
In which phase do growth factors play a crucial role in determining whether a cell proceeds with division or enters a quiescent state?
G1 phase
Which phase is typically the shortest in duration for a mammalian cell with a 16-hour cycle?
M phase
What is the primary mechanism by which DNA polymerase ensures high fidelity during DNA replication?
DNA polymerase has a proofreading mechanism that can detect and correct errors before the next nucleotide is added
What is the primary reason that the error rate during DNA replication is much lower than the error rate during transcription (RNA polymerase)?
DNA replication has additional proofreading mechanisms that transcription lacks
What is the primary function of the 3'-to-5' exonuclease activity of DNA polymerase during proofreading?
It removes incorrectly added nucleotides from the 3' end of the DNA strand
Which of the following is NOT a proofreading mechanism used by DNA polymerase during DNA replication?
A separate mismatch repair system corrects errors made during replication
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)?
DNA replication has more proofreading mechanisms than transcription
What is the primary function of the strand-directed mismatch repair system mentioned in the text?
It is not a proofreading mechanism used by DNA polymerase during replication
What is the role of DNA ligase in DNA replication?
Joins the 3’ end of a new DNA fragment with the 5’ end of the previous fragment
How does DNA topoisomerase contribute to DNA replication?
Relieves supercoiling tension
What is a key function of histone chaperones during DNA replication?
Packaging newly replicated DNA into nucleosomes
Which enzyme is responsible for relieving supercoiling tension during DNA replication?
DNA topoisomerase
In DNA replication, what is the main task of DNA topoisomerase?
Managing supercoiling tension
During which phase of the cell cycle is histone synthesis primarily carried out in eukaryotes?
S phase
Test your knowledge on cell cycle checkpoints and regulation mechanisms in eukaryotic cells. Explore how factors within the cell and external signals influence the progression through different stages of the cell cycle.
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