Cyclin-Dependent Kinases and Cell Cycle

The video explains the role of cyclins and cyclin-dependent kinases (CDKs) in cell cycle regulation. Cyclins are proteins that undergo synthesis and degradation in a cyclic manner, partnering with CDKs to phosphorylate target proteins. The video details the specific cyclin-CDK complexes active in different cell cycle phases, such as G1, S, and M phases. It also covers the regulation of these complexes, focusing on Cyclin B-CDK1, and describes the activation and inhibition mechanisms involving phosphorylation. The video concludes with a summary of cyclin-CDK regulation.

What is the primary role of cyclin-dependent kinases (CDKs) in the cell cycle?

• To transport molecules across the cell membrane

• To degrade proteins

• To phosphorylate downstream proteins

• To synthesize DNA

Why are cyclins named as such?

• They form circular complexes with CDKs

• They are involved in circular DNA replication

• They are produced and degraded in a cyclic manner

• They are circular in shape

During which phase is the G1 cyclin most active?

• G2 phase

• M phase

• S phase

• G1 phase

Which cyclin-CDK complex is primarily involved in the S phase of the cell cycle?

• Cyclin D and CDK4

• Cyclin E and CDK2

• Cyclin B and CDK1

• Cyclin A and CDK6

What is the role of cyclin B in the cell cycle?

• It is involved in DNA replication

• It degrades proteins

• It regulates the mitotic phase

• It initiates the G1 phase

Which cyclin is associated with the G1 phase and has CDK4 or CDK6 as partners?

• Cyclin E

• Cyclin D

• Cyclin B

• Cyclin A

Which enzyme is responsible for activating CDKs by phosphorylation?

• CDK activating kinase

• CDC25 phosphatase

• Inhibitory kinase

• Cyclin D

What is the function of CDC25 in the regulation of cyclin-CDK complexes?

• It synthesizes CDKs

• It degrades cyclins

• It removes inhibitory phosphates

• It adds inhibitory phosphates

Which residues are phosphorylated by inhibitory kinases to inactivate CDKs?

• Threonine 61 and Tyrosine 15

• Threonine 14 and Tyrosine 15

• Tyrosine 10 and Serine 15

• Serine 10 and Threonine 20

What happens to the cyclin B-CDK1 complex at the end of the G2 phase?

• It is degraded

• It becomes inactive

• It is synthesized

• It becomes active