ch 18

Question 1

Describe in very general terms, what is happening in each phase of the cell cycle, including G0

Answer 1

G0 phase: inactive phase
G1 phase: cell is growing; serves as a time of decision-making for the cell
S phase: DNA synthesis
G2 Phase: cell is growing; makes sure cell is ready to proceed to next phase
M Phase: mitosis and cytokinesis

Question 2

Explain how cyclins and cyclin-dependent kinases work together to control transition from one phase of the cycle to the next

Answer 2

To become enzymatically active, cyclins must bind to the CDK, once this happens the active cyclin-CDK complex phosphorylates key proteins in the cell that are required to initiate particular steps in the cell cycle. The cyclin also helps direct the CDK to target proteins

Question 3

Explain how p53 and p21 act together to stop cells with damaged DNA from continuing to progress through the cycle.

Answer 3

When DNA is damaged, specific protein kinases respond by both activating the p53 protein. The activated p53 thus accumulates and stimulates the transcription of the gene that encodes the CDK inhibitor p21. The p21 protein binds to G1/S-CDK and S-CDK and inactivates them, so that the cell cycle arrests in G1.

Question 4

Define apoptosis

Answer 4

controlled form of programmed cell death that allows excess cells to be eliminated from an adult or developing organism

Question 5

Bad (or Bax)

Answer 5

promotes cell death by inducing the release of cytochrome c from the mitochondria into the cytosol

Question 6

BCl2

Answer 6

inhibits apoptosis by preventing Bax and Bak from releasing cytochrome C

Question 7

Akt

Answer 7

phosphorylates Bad and inactivates it

Question 8

Cytochrome C

Answer 8

induces cell death by promoting the assembly of an apoptosome

Question 9

Caspases

Answer 9

mediates the destruction of the cell by apoptosis when activated