23 Cell cycle

Question 1

What are the three functional aspects of the cell cycle?

Answer 1

1. cell growth and chromosome replication
2. chromosome segregation
3. cell division

Question 2

Three major events that occur in cell cycle are what?

Answer 2

1. S phase: DNA replication
2. M phase: chromosome segregation and cell division
3. cytokinesis

Question 3

Interphase consists of waht phases of cell cycle?

Answer 3

1. G1, S, G2

Question 4

When does M phase occur?

Answer 4

1. after G2, for only 1 hour. not majority of cell life

Question 5

Where are the regulatory control points that permit/inhibit cell cycle progression?

Answer 5

1. Start checkpoin from G1 into S phase (restriction point)
2. G2/m phase: proper chromosome alignment in metaphase
3. met-anaphase check: triggers chromatid separation and cytokinesis

Question 6

What are fission yeast?

Answer 6

1. model organism for cell cycle study

2. grow at ends by elongation

Question 7

What are budding yeast?

Answer 7

1. model organism of cell cycle

2. oval yeast, divide by budding

Question 8

What is cdc gene?

Answer 8

cell-division cycle genes

Question 9

What is used to activate various steps of the cell cycle?

Answer 9

1. cyclin dependent kinases can activate specific proteins at the proper time to induce activation

Question 10

What governs the cell cycle?

Answer 10

cyclin-dependent kinases.

– [cdks] does not change over time, only the activity of activating various steps

Question 11

What is a cyclin?

Answer 11

1. protein that regulates the activity of cdks
2. [cyclins] subject to change in order to adjust activity of cdks
3. specific to the point in the cell cycle

Question 12

What are the different classes of cyclins?

Answer 12

1. G1/S
2. S
3. M

Question 13

G1/S cyclins

Answer 13

1. activate late G1 cdks

2. level drop in S phase, as we don’t want to trigger starting DNA replication more than once

Question 14

S cyclins

Answer 14

1. bind cdk after start
2. chromosome replication
3. high until mitosis, prevents secondary binding at replication origin or proteins

Question 15

M cyclins

Answer 15

1. cdks stimulate mitosis entry G2/M checkpoint

2. removed mid-mitosis

Question 16

The cdks have activation by cyclins, and what else has to occur in order to fully activate them?

Answer 16

1. cdk-activating kinase must act to remove the T-loop from the active site of the cyclin, to allow full activation of cdk

Question 17

What is the function of Wee1 kinase?

Answer 17

1. adds inhibitory phosphate to Cdk, at the roof site. Cdk is inhibited

Question 18

What is the function of cdc25?

Answer 18

1. removal of roof phosphate to cause activation of Cdk

Question 19

What are CKI?

Answer 19

Cdk inhibitory proteins, second method to inhibit Cdk activity

Question 20

When are CKI most commonly used?

Answer 20

1. G1/S and S Cdks

Question 21

What is INK4?

Answer 21

1. CKI of G1 cell cycle phase.

2. mutation leads to hereditary melanoma

Question 22

What are p53 and p21?

Answer 22

1. p53: tumor suppressor gene

2. p21: CKI under direct influence of p53, to stop cell division

Question 23

The protein SCF-ubiquitin ligase has what role in cell cycle?

Answer 23

1. adds ubiquitin to proteins, to mark them for degradation
2. can add to CKI, to promote cell division
3. F box protein is rate determining factor

Question 24

The activation of M-Cdk has what effect in terms of regulation?

Answer 24

1. positive feedback loop for activating cdc25, to remove roof phosphate from cdk
2. inhibition of Wee1 from adding roof phosphate

Question 25

What triggers progression from metaphase to anaphase?

Answer 25

1. protein degradation 2. facilitated by APC/C (anaphase promoting complex) 3. ubiquitin ligase

Question 26

What major proteins are affected during anaphase, when the APC/C is activated?

Answer 26

1. securin is degraded, which protects cohesin from degradation 2. cohesin is degraded, which holds the sister chromatids together until this point to allow for separation

Question 27

How can cyclin-cdk activity be regulated?

Answer 27

1. cdk phosphorylation 2. CKI binding 3. cyclin proteolysis 4. protein ubiquitination

Question 28

At what phases of cell cycle is chromosome duplication under control?

Answer 28

1. G1 with formation of PRE-RC, prereplicative complex | 2. S phase, during replication fork formation

Question 29

What assembles during G1 phase to ensure on 1 copy of DNA is made?

Answer 29

1. PRE-RC (prereplicative complex) | 2. binds to the replication origin preventing origin proteins from binding

Question 30

What assembles during S phase of cell cycle to control chromosome duplication?

Answer 30

1.replication forks, prevent complete trascription/copying of DNA strand

Question 31

PRE-RC is preset in G1 phase, what prevents this protein from being present during S and M phase of cell cycle?

Answer 31

1. cdks inhibit the formation of PRE-RC during S and M phase. 2. deletion of all cdks is required before entering G1, so PRE-RC can regain function and only allow 1 round of chromosomal copying