Lecture 22 - Cell Cycle II (Ch. 18)

What is the primary function of the cell-cycle control system?

A. To synthesize new organelles randomly

B. To ensure cell-cycle events occur in a set sequence and are completed before the next begins

C. To prevent the cell from ever entering the S phase

D. To facilitate cell death in all conditions

B

Which checkpoint ensures the environment is favorable before the cell commits to DNA replication?

A. G2 to M transition

B. Metaphase to Anaphase transition

C. G1 to S transition (Start)

D. Cytokinesis checkpoint

C

At the G2/M checkpoint, the control system primarily checks for:

A. Proper attachment of chromosomes to the spindle

B. DNA damage and completion of DNA replication

C. Sufficient levels of glucose in the blood

D. The presence of a cell wall

B

What must happen for the cell to progress from Metaphase to Anaphase?

A. All DNA must be replicated

B. The cell must reach a certain size

C. All chromosomes must be properly attached to the mitotic spindle

D. The nuclear envelope must reform

C

What is required for a Cdk to become enzymatically active?

A. It must be degraded by a proteasome

B. It must bind to a specific cyclin protein

C. It must be exported from the nucleus

D. It must bind to a ribosome

B

How do cyclin levels change throughout the cell cycle?

A. They remain constant at all times

B. They fluctuate in a cyclical fashion

C. They only increase during the M phase

D. They decrease immediately after G1

B

Which cyclin-Cdk complex is responsible for driving the cell into mitosis?

A. G1-Cdk

B. G1/S-Cdk

C. S-Cdk

D. M-Cdk

B

The rapid fall of cyclin concentrations during the cell cycle is primarily due to:

A. Targeted degradation via the anaphase-promoting complex (APC/C)

B. Translation of cyclin mRNA being blocked

C. Secretion of cyclins out of the cell

D. Reversal of the cell cycle to G0

D

What does the APC/C tag cyclins with to mark them for destruction?

A. Phosphate groups

B. Ubiquitin chains

C. Methyl groups

D. Acetyl groups

A

Besides cyclin binding, what else is required for a Cdk to be fully active?

A. Dephosphorylation by Wee1

B. Phosphorylation at a specific activating site

C. Attachment to the cell membrane

D. Binding to DNA

B

Which protein acts as an inhibitory kinase by adding a phosphate to Cdk to keep it inactive?

A. Cdc25

B. Wee1

C. p21

D. p27

B

Which protein acts as an inhibitory kinase by adding a phosphate to Cdk to keep it inactive?

A. Cdc25

B. Wee1

C. p21

D. p27

B

The phosphatase that removes inhibitory phosphates from Cdk to activate the complex is:

A. APC/C

B. Cdc25

C. p53

D. Rb

B

What is the role of Cdk inhibitor proteins like p27?

A. They phosphorylate the Cdk

B. They bind to the cyclin-Cdk complex to block its activity

C. They promote the transition to the S phase

D. They help assemble the spindle

B

What is the "resting state" that cells enter if environment conditions are unfavorable in G1?

A. G2

B. S

C. G0

D. M

C

Which extracellular signals stimulate animal cells to multiply?

A. Antigens

B. Mitogens

C. Myosins

D. Condensins

B

What is the molecular "brake" that prevents cells from entering the S phase by inhibiting transcription?

A. p53

B. Rb (Retinoblastoma) protein

C. Cyclin D

D. Helicase

B

How do mitogens trigger the cell cycle to proceed?

A. They activate G1-Cdk, which phosphorylates and inactivates Rb

B. They destroy all Cdks in the cell

C. They bind directly to DNA to start replication

D. They prevent the formation of cyclins

A

Which protein is known as the "guardian of the genome" and increases in response to DNA damage?

A. Rb

B. p53

C. Cdc6

D. Separase

B

Activated p53 promotes the transcription of which Cdk inhibitor?

A. p21

B. p27

C. Wee1

D. Mad2

A

Which protein binds to the Origin Recognition Complex (ORC) in G1 to prepare for DNA replication?

A. Cdc25

B. Cdc6

C. p53

D. Ubiquitin

B

S-Cdk triggers DNA replication and prevents re-replication by:

A. Degrading the DNA polymerase

B. Phosphorylating Cdc6, leading to its degradation

C. Activating Wee1

D. Reforming the nuclear envelope

B

If DNA is incompletely replicated, which protein is inhibited to prevent the cell from entering M phase?

A. Rb

B. Cdc25

C. p21

D. Cohesin

B

The positive feedback loop in M-Cdk activation involves M-Cdk activating more of its own activator, which is:

A. Wee1

B. Cdc25

C. p53

D. APC/C

B

Which of the following is NOT a target of M-Cdk?

A. Condensins

B. Nuclear lamins

C. Myosin light-chain kinase

D. Ribosomal RNA

D

The spindle checkpoint delays anaphase until:

A. DNA is fully repaired

B. All chromosomes are stably attached to the spindle

C. The cell has doubled in size

D. The nuclear envelope has reformed

B

Unattached kinetochores send a signal that inhibits which complex?

A. S-Cdk

B. APC/C

C. p53

D. ORC

B

Which protein must be degraded by APC/C to allow the activation of separase?

A. Securin

B. Cohesin

C. Cyclin B

D. Rb

A

What does the enzyme separase do?

A. It replicates DNA

B. It cleaves cohesin complexes to separate sister chromatids

C. It builds the cell plate in plants

D. It phosphorylates p53

B

Which kinase is inhibited by M-Cdk to ensure the Cdk remains active?

A. Cdc25

B. Wee1

C. Mitogen

D. Integrin

B