Cell Cycle 2

Question 1

What is the role of the G1 cyclins?

Answer 1

Bind and activate Cdks which stimulate entry into a new cell at the Start

Question 2

What is the role of G1/S cyclins?

Answer 2

activates Cdks that stimulate progression through Start, resulting commitment to cell cycle entry

Question 3

What is the role of S cyclins?

Answer 3

Cyclin activates Cdks necessary for DNA synthesis and contribute to the control of some of the early mitotic events

Question 4

What is the role of the M cyclins

Answer 4

Cyclins activates Cdks necessary for entry into mitosis

Question 5

What does the G1 Cyclins concentration depend on?

Answer 5

Depends on the rate of cell growth

Question 6

When does the G1/S cyclin concentration peak?

Answer 6

Concentration peaks in late

Question 7

What happens to the S cyclins concentration during S phase?

Answer 7

Concentration rises and remains high during S cyclins

Question 8

When does the M cyclins concentration increase and then peak?

Answer 8

M cyclins concentration rises in mitosis then peaks in metaphase

Question 9

How do different Cyclin–Cdk complexes trigger different cell-cycle events?

Answer 9

Cyclins binds to different Cdks
The cyclins both activate and directs Cdks to specific target protein. The same complexes can induce different events at a different time in the cycle due to availability of the substrates

Question 10

What controls Cdk activity?

Answer 10

Inhibitory phosphorylation

Question 11

The active Cyclin-Cdk complex can be inhibited by what?

Answer 11

Phosphorylation at 1 or 2 sites in the active site of the enzyme,
Phos, of Tyr 15 by Wee1 or
Tyr 14 and Tyr 15 by Myt 1

Question 12

Define Cdk inhibitor protein

Answer 12

protein that interacts with Cdks or Cdk–cyclin complexes to block their activity, usually during G1 or in response to inhibitory signals from the environment or damaged DNA

Question 13

Describe the regulation of the cell cycle starting at transiton though G1

Answer 13

Signals from outside (growth factors) are detected
activation of a signaling pathway leads to the activation of the G1/S-Cdk, which in turn via phosphorylation of Rb protein allows E2F factor to express genes needed for S phase

Question 14

Describe the regulation of the cell cycle starting as the G1 arrest

Answer 14

Regulation involves signal transduction via multi-step signalling pathways, and transcriptional regulation

Question 15

Name the 3 activators of SCF complexes

Answer 15

Skp2
FBW7
Beta-TRCP

Question 16

Name 2 activators of APC/C complexes?

Answer 16

Cdc20

Cdh1

Question 17

Control of mitosis by APC/C

Answer 17

M-Cdk activity promotes metaphase and activity of APC/C ^CDc20 which triggers anaphase and CDk inactivation and triggering APC^Cdh1 for G1

Question 18

Progression through the cell cycle is governed at three major checkpoints.

What are these

Answer 18

In mid to late G1, Cdks are activated by G1/S- and S-phase cyclins, resulting in entry into the cell cycle at Start.

Entry into mitosis (at the G2/M checkpoint) is triggered by activation of M-phase Cdk– cyclin complexes.

Finally, the metaphase-to-anaphase transition is driven by Anaphase Promoting Complex/Cyclosome (APC/C), which triggers the destruction of cyclins and other regulators

Question 19

What are the four phases in the Eukaryotic cell cycle?

Answer 19

G1
S
G2
M