Biochemistry Multiple Choice Questions on “Regulation of the Cell Cycle by Protein Kinases”.
1. Which of the following statements regarding cyclin-dependent protein kinase is not correct?
A. Their activity is regulated by cyclins
B. They can alter the activity of proteins involve in the progression of cells through cell cycle
C. Their activity fluctuates during cell cycle
D. Each type of cell contains one specific form
e) Their activity is regulated by changes in gene expression, protein phosphorylation and proteolysis
Answer: C
Clarification: They remain constant throughout cell cycle.
2. Which of the following statements regarding cyclins is not correct?
A. They can become linked to ubiquitin
B. They catalyze the phosphorylation of protein
C. They contain a specific amino acid sequence that target them for proteolysis
D. They are activated and degraded during cell cycle
Answer: D
Clarification: They activate cdk enzymes.
3. What is Ubiquitin?
A. Protein kinase
B. Protease
C. Component of the electron transport system
D. Protein that tags another protein for proteolysis
Answer: D
Clarification: Ubiquitin binds to a substrate protein resulting in their degradation.
4. Cdk2/cyclinE functions in ____________
A. G2/M transition
B. G2
C. M
D. G1/S transition
Answer: D
Clarification: Cdk1/cyclinB functions in M phase Cdk2/cyclinA functions in S phase, G2 phase.
5. In which phase of cell cycle is DNA replicated?
A. G1 phase
B. S phase
C. G2 phase
D. M phase
Answer: B
Clarification: During the S phase, DNA replication takes place.
6. Cyclin dependent kinases which control progression through cell cycle checkpoints are totally activated by which of the following?
A. Binding to cyclin, plus phosphorylation by a Cdk activating protein kinase
B. Binding to cyclins
C. Phosphorylation by Cdk activating protein kinase
D. Phosphorylation by a tyrosine kinase
Answer: A
Clarification: Cyclin dependent kinases are totally activated by binding to cyclin and phosphorylation by a Cdk activating protein kinase.
7. At the end of each phase of cell cycle cyclins activating Cdks in that phase are inactivated irreversibly by _____________
A. Multiple phosphorylations
B. De-phosphorylation
C. Ubiquitinylation
D. Destabilizing by proteolysis in a proteosome
Answer: D
Clarification: At the end of each phase of cell cycle, cyclins are inactivated irreversibly by destabilizing by proteolysis in a proteasome.
8. At which cell cycle checkpoint, cell cycle is halted if cell’s DNA is damaged?
A. G1 – S
B. S – G2
C. G2 – M
D. G0 – G1
Answer: A
Clarification: During G1 phase cell grows and during S phase DNA replicates. So there must be a checkpoint between these two phases to check if there is a damage in DNA.
9. Which of the following occurs in meiosis but not in mitosis?
A. Attachment of spindle fibers to kinetochore
B. Replication of DNA prior to start of cell division
C. Separation of sister chromatids at anaphase
D. Pairing of homologous chromosomes at metaphase plate
Answer: D
Clarification: Pairing of homologous chromosomes at metaphase plate does not occur in mitosis.
10. Passage of a cell through stages of cell cycle is controlled by a protein kinase that phosphorylates many different proteins at appropriate times.
A. Cdk activating kinase
B. Cyclin-dependent kinase
C. Cyclins
D. Tyrosine kinase
Answer: B
Clarification: Passage of a cell through stages of cell cycle is controlled by Cdk.
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