1.4 - Cell Cycle Control

Question 1

4 phases of cell cycle (4)

Answer 1

1. M - mitosis
2. G1 - Gap1
3. S - synthesis
4. G2 - Gap2

Question 2

conditions that must be right for cell division to occur (checkpoints) (3)

Answer 2

1. is the cell big enough? - cell growth
2. is the environment favourable?
3. DNA integrity? - DNA damage/problems during replication

Question 3

genetic approaches to understanding cell cycle (studies in 2 single cell eukaryotic organisms crucial for understanding cell cycle control) (2)

Answer 3

1. budding yeast (saccharomyces cerevisiae)
2. fission yeast (schizosaccharomyces pombe)

Question 4

budding yeast (saccharomyces cerevisiae) division

Answer 4

divides by budding

Question 5

fission yeast (schizosaccharomyces pombe) division

Answer 5

cells grow lengthwise until they reach critical size before going into mitosis and divide by medial fission

Question 6

what will a ts mutation in a random essential gene lead to?

Answer 6

the cell arresting across the cell cycle

Question 7

what will a ts mutation in a cell cycle regulator gene lead to?

Answer 7

arrest at a discrete cell cycle stage

Question 8

Cdc mutation at 36°C

Answer 8

cannot divide to form 2 cells

Question 9

wee mutant at 36°C

Answer 9

divides too early to form 2 cells

Question 10

master cell cycle regulator

Answer 10

Cdc2

Question 11

mutations identified by Cdc2 screen (3)

Answer 11

1. mutants that block in S
2. mutants that block in G1
3. mutants that block in G2

Question 12

what is required for G1/S and G2/M?

Answer 12

Cdc25

Question 13

do wee mutations delay cell cycle?

Answer 13

no, they divide to produce small G1 cells

Question 14

Cdc2 mutant variations (2)

Answer 14

1. Cdc
2. Wee

Question 15

role of wee1

Answer 15

negatively regulates movement from G2 -> M (inhibits mitosis)

Question 16

role of Cdc25

Answer 16

positively regulates movement from G2 -> M (activates mitosis)

Question 17

what happens to cyclins throughout each cell cycle?

Answer 17

made and destroyed each cell cycle (cyclin proteins accumulated as cells progress through cell cycle)

Question 18

mitosis promoting factor in mitotic nuclei

Answer 18

MPF - promotes metaphase

Question 19

mitosis promoting factor (MPF) enzyme identity

Answer 19

active mitotic CDK complex

Question 20

mitosis promoting factor (MPF) complex structure

Answer 20

complex between a 34kD serine/threonine protein kinase

Question 21

what kind of enzyme is cdc2

Answer 21

cyclin-dependant protein kinase (CDK)

Question 22

CDK

Answer 22

cyclin dependant protein kinase

Question 23

what does CDK regulation ensure?

Answer 23

ordered progression through the cell cycle (look at one note diagram)

Question 24

what does M-CDK do when its activity has successfully brought about cell state required for cell division?

Answer 24

it helps trigger its own destruction by promoting the activation of APC which ubiquitylates cyclins leading to their destruction

Question 25

what controls progression through mitosis?

Answer 25

MPF/Mitotic CDK

Question 26

one of the most important events during G1/S

Answer 26

transition between preparing DNA for replication in G1 and performing DNA replication in S (making sure the cell does not try to re-replicate already replicated DNA)

Question 27

licenses

Answer 27

permits DNA to be replicated (cells are licensed to go through S phase once in a cell cycle)

Question 28

when is licensing occuring/ inihibited (2)

Answer 28

1. occurs in G1 2. inhibited in S phase (when the already licensed DNA is replicated)

Question 29

2 main groups of cyclin/CDK complexes in humans? (2)

Answer 29

1. G1/S - control entry into S phase 2. G2/M - control entry into mitosis

Question 30

cell cycle is a CDK cycle (7)

Answer 30

1. low Cdk activity (loading of licensing factors at origin) 2. S-cyclin increases 3. S-Cdk activated replication 4. S-Cdk activity high (no relicensing) 5. M-cyclin increases 6. M-Cdk activated, triggers mitosis 7. after spindle checkpoint satisfied, APC activated and cyclins destroyed, resetting cycle

Question 31

checkpoints

Answer 31

cells delay cell cycle progression in response to external signals (e.g. DNA damage)

Question 32

major transition points/checkpoints in interphase (2)

Answer 32

1. START - cells licensed in G1 to enter S phase 2. G2/M transition

Question 33

how is the Cdk/cyclin complex kept inactive/activated (2)

Answer 33

1. kept inactive - Wee1 2. activated - Cdc25

Question 34

spindle checkpoint role (2)

Answer 34

1. monitors whether cells assemble their chromosomes and spindles correctly (occupancy of kinetochores/tension) 2. ensures all chromosomes lined up on metaphase plate and attached to microtubules to both poles before anaphase is triggered

Question 35

role of MAD proteins

Answer 35

inhibits separation at unattached kinetochores (prevent activation of APC)

Question 36

APC

Answer 36

anaphase promoting complex

Question 37

role of APC

Answer 37

targets cyclin proteins for destruction (essential to exit mitosis and keep cell cycle moving)