Week 5- cell division- Holy

Question 1

define G0

Answer 1

G0-cells leave the cell cycle- no more cells are needed

Question 2

time spent in

1) S phase
2) M phase

Answer 2

1) 8-12 hrs

2) 1 hr

Question 3

G1

Answer 3

gap 1- decision whether or not to divide

if cell decides to divide it passes “start” point and now it is committed to starting DNA synthesis and entering mitosis

Question 4

S phase

Answer 4

where DNA synthesis occurs (xsomes and centrosomes replicate)

• after xsome rep is complete, daughter xsomes (called chromatids) remain connected to each other at the centromere
• specific DNA-binding centromeric proteins are attached to and identify this region

Question 5

G2

Answer 5

after DNA syn, cells do not immediately divide (G2)

xsomes condense to prepare for mitosis

Question 6

proteins responsible for driving the cell cycle

Answer 6

CDK’s and cyclins

Question 7

cohesions

Answer 7

Cohesions- multi-protein complexes that help keep replicated xsome pairs (daughter chromatids) together, by encircling them, until the time when it is appropriate to separate them

Question 8

condensins

Answer 8

multi-protein complexes that are involved in xomse condensations (condense so they can be more easily separated)

Question 9

most important feature of mitosis

Answer 9

each daughter cell receives a complete set of all the xsomes originally present in the mother cell ==> identical daughter cells

Question 10

what proteins are responsible for driving the cell cycle

how do they do this

Answer 10

CDK’s and cyclins
cyclins bind to CDK’s to form a complex that can further phosphorylate regulatory and transcription factors to help move the cell cycle along.

Question 11

how are CDK’s and cyclins regulated

Answer 11

regulated by being phosphorylated/dephosphorylated

Question 12

Wee1 kinase

Answer 12

adds a phosphate that inactivates Cdk’s, and Cdc25 phosphatase removes the phosphate to activate it

Question 13

Cki’s (p27)

Answer 13

proteins that bind to the cyclin-Cdk complex to inactivate it

Question 14

3 ways to regulate CDK activity

Answer 14

1) presence of cyclin
2) specific patterns of CDK phosphorylation
3) presence of Cki’s

Question 15

How are positive feedback loops used in cell cycle regulation?

Answer 15

Positive feedback works to activate more Cdc25 to activate more Cdk’s, and inhibits Wee1 to inhibit its deactivating activity

Question 16

cyclin/CDK pairs that drive:
G1
M

Answer 16

G1: Cyclin D, CDK4 or 6
M: Cyclin B, CDK1

Question 17

best pathway for cell cycle regulation

Answer 17

growth factor signaling

Question 18

regulation of G1/GO phase (MAP kinase pathway)

Answer 18

growth factors(mitrogen) dimerize and activate Ras ⇒ activates MAP kinase cascade ⇒ a P’d Map Kinase can enter the nuclease ⇒ activate transcription factors via phosphorylation ⇒ transcribe early response genes (Myc)⇒ Myc activates transcription of late response genes (cyclin D) ⇒ Cyclin D binds to CDK and becomes active ⇒ active Cdk complex phosphorylates Rb gene (which normally inhibits a transcription factor- E2F)⇒ phosphorylated Rb gene in now inactive which menas E2F can be active ⇒ E2F activates transcription of S phase cyclins to proceed with S phase

Question 19

Rb

Answer 19

when phosphorylated it is inactive and can’t in turn inactivate E2F

Question 20

E2F transcription factor

Answer 20

activates transcription of of S phase cyclins when Rb is inactive (P’d)
activate genes that make proteins needed to DNA rep

Question 21

purpose of Myc genes

Answer 21

to activate genes that encode for cyclin D which can bind to CDK

Question 22

ORC’s

Answer 22

ORC’s- origins of replication- where replication can begin (multiple of these on xsomes)

Question 23

what triggers S phase

Answer 23

triggered by production of S phase cyclins from the cyclin-D complex from G1

Question 24

pre-RC

Answer 24

early in G1, a complex of initiator proteins assembles on replication origins for form pre-replication complex

Question 25

when can pre-RC bind to replication origins

Answer 25

can only bind when unphosohorylated
-since they are substrates of CDK, they can only bind in G1, when the overall CDK activity is low (or else they would get P’d)

Question 26

what divides the cytoplasm during cytokinesis

Answer 26

a contractile ring made up of actin and myosin

Question 27

steps for entering M phase

Answer 27

M-Cyclin (Cyclin B) increases ⇒ cyclin B associates with CDK1 forming M-CDK ⇒ M-CDK is phosphorylated by an inhibitory kinase (Wee1) and an activating kinase (CAK) ⇒ inhibitory P’s keep M-CDK activity low ⇒ when Cdc25 gets activated (by phosphorylation) it removes the inhibitory P’s form M-CDK

Question 28

where are the cell cycle check points

Answer 28

1) entering S phase
2) entering M phase
3) leaving M phase

Question 29

how is p53 used in cell cycle check points

Answer 29

DNA damage → activation of ATM/ATR which then activates Chk1/Chk2 kinase → Chk1/Chk2 phosphorylate p53 and activate it (causing release of Mdm2) → p53 binds to DNA to promote p21 gene → p21 gene makes CKI’s that inhibit cyclin/Cdk to halt cell cycle