Cell Cycle

Question 1

describe the G0 phase

Answer 1

also known as ‘quiescence’, cells not actively dividing

Question 2

give an example of a cell which stays in the G0 phase and a cell which may leave the G0 phase

Answer 2

erythrocytes stay in G0

lymphocytes may leave G0 upon activation by an external signal

Question 3

describe what happens in the G1 and G2 phases

Answer 3

G1, cell growth, monitoring environment, RNA/protein synthesis for S phase prep, growth-factor development

G2, further growth, organelle replication, mitosis prep

Question 4

what do CDKs do?

Answer 4

regulate cell cycle progression in serine/threonine kinases

Question 5

what 3 things tightly regulate CDK activity?

Answer 5

cyclin presence/absense
phosphorylation/dephosphorylation
CKIs

Question 6

what are cyclins?

Answer 6

unstable activator proteins that are up or down regulated depending on cell cycle phase

Question 7

what are CKIs and how do they function?

Answer 7

CDK inhibitors - small proteins blocking cyclin/CDK activity

function by forming an inactive complex or acting as a competitive CDK ligand

Question 8

what are the 3 CKI families?

Answer 8

p21 CIP
p27 KIP
p16 INK

Question 9

name 3 ways maturation promoting factor helps cells progress from G2 to M phase, and name the molecules phosphorylised

Answer 9

nuclear enveloped destroyed (lamins)
chromosome condensation (histones/condensins)
spindle formation (mictotubule associated proteins/MAPs)

Question 10

name 6 things that must be monitored for cell progression to safely occur

Answer 10

growth factor presence
sufficient growth
DNA damage
replication errors
spindle attachment
chromosome integrity

Question 11

describe the restriction point, what cyclin it is dependant on, and the ‘gatekeeper’ of it

Answer 11

the point in which progression may continue depending on the level of growth factor signals present in the cell
dependant on cyclin D accumulation
gatekept by RB

Question 12

explain the role of Rb and CDK-cyclin D in cell cycle regulation

Answer 12

if no growth factor signals detected, Rb binds to transcription factor E2F, inhibiting transcription

if growth factor signals detected, cyclin D is produced and forms CDK-cyclin D complex, which phosphorylates Rb so it cant bind to E2F, allowing transcription to occur

Question 13

what do tumour suppressor genes (TSGs) do?

Answer 13

encode normal cell proteins that inhibit cells proliferation and growth
cause cell cycle arrest or repair DNA damage

Question 14

name 3 examples of TSGs and how they work

Answer 14

RB - blocks entry to cell cycle
p53 - detects DNA damage
BRCA1 - DNA repair

Question 15

explain the process of halting the cell cycle at DNA damage checkpoints (G1-S and G2-M)

Answer 15

DNA damage detected, p53 released, causes production of p21 (CKI) which inhibits production of CDK-cyclins results in no progression

G1-S: CDK2-cyclin E/A
G2-M: CDK1-cyclin A/B

Question 16

descibe the role of p53 in response to different levels of DNA damage

Answer 16

p53 is a transcription factor
low levels - p21 expression to halt cell cycle so DNA can be repaired
high levels - promotes genes/molecules coding for apoptosis

Question 17

describe the process of the metaphase/spindle checkpoint

Answer 17

surveillance mechanism delaying anaphase by inhibiting anaphase promoting complex (APC) until all chromosomes are attached to spindle fibres

Question 18

which cyclin is necessary for entry into M phase?
which CDK requires this cyclin to be active for M phase entry?

Answer 18

cyclin B
CDK 1

Question 19

what does CDK 1/cyclin B phosphorylate?

Answer 19

lamins, condensins

Question 20

what cyclin and CDK complex regulates cell entry into S phase and what does it phosphorylate?

Answer 20

CDK4/6, cyclin D
phosphorylates Rb protein

Question 21

what are the main checkpoints in the cell cycle?

Answer 21

restriction point (G1)
DNA damage (G1 -> S and G2 -> M)
metaphase checkpoint

Question 22

explain the importance of growth factors in the restriction point

Answer 22

cell cycle progression determined by GF presence
restriction point = cell no longer needs GFs after this point (commits to cell cycle)