Cell cycle intro

Question 1

What are the 4 phases of the cell cycle?

Answer 1

G1
S
G2
M

Question 2

What occurs during G1?

Answer 2

Growth of daughter cells after cytokinesis
Monitor environment for signals for growth
Varies in length
Restriction point

Question 3

What is the restriction point of G1?

Answer 3

RAS dependent pathways for transcription factors that activate by binding mitogen to the transmembrane receptor

Controlled by CDKs - cdk2, cdk4, and cdk6
Regulated by cyclin D and cyclin E to activate CDKs

Question 4

How are CDKs regulated?

Answer 4

Inhibited by phosphorylation at active site by Wee1
Dephosphorylated by cdc25 - activates

Question 5

How do CDKs work?

Answer 5

Activated by cyclins
Phosphorylates RB into pRB

Question 6

What is pRB and how does it function in the cell cycle?

Answer 6

Retinoblastoma protein - tumor suppressor
Binds E2F transcription factors when it is not phosphorylated, which prevents cell growth
Inhibited by phosphorylation, which is done by cdk4/cyclin D, cdk6/cyclin D, and cdk2/cycle E - this releases E2F

Question 7

What is p53 in G1?

Answer 7

Transcription factor
Tumor suppressor
Stimulates production of p21, which inhibits cdk2

Question 8

What are some cdk inhibitors?

Answer 8

CIP/KIP family (p21, p27, p57) - inhibit cdk2
INK4 family (p14, p16, p18, p19)

Question 9

How does p16 influence the G1 phase of the cell cycle?

Answer 9

Inhibits cdk4 and cdk6

Question 10

What is the S phase and how is it regulated?

Answer 10

Replication of DNA’

cdk2/cyclin A

Question 11

What is G2?

Answer 11

Builds up cell contents in preparation for division
Chromatin organize for mitosis
Checks for DNA damages or errors

Question 12

How is G2 regulated?

Answer 12

cdk2/cyclin A

cdk1 inactivated by wee1 kinase and activated by cbc25 phosphatase

Similar processes to G1

Question 13

What regulates entry into mitosis?

Answer 13

cdk1/cyclin B
p53 kinase - lamin kinase - for breakdown of nuclear envelope and chromatin condensation.

Question 14

What is G0?

Answer 14

Resting state in response to signals to stop growth
No synthesis of cell cycle proteins
Most will eventually die via apoptosis

Question 15

By what reasons may a cell enter G0?

Answer 15

Adequate growth - shortened telomeres
Terminally differentiated cells withdraw from cell cycle

Question 16

What are the phases of Mitosis?

Answer 16

Prophase
Prometaphase
Metaphase
Anaphase
Telophase
Cytokinesis

Question 17

What is interphase?

Answer 17

G1, S, G2

Question 18

What occurs during prophase?

Answer 18

2 centrosomes and mitotic spindle begins to form
Sister chromatids bound by centromere
Nucleolus disassembles

Question 19

What occurs during prometaphase?

Answer 19

Nuclear envelope disassembles

Question 20

What occurs during metaphase?

Answer 20

Chromatids align at metaphase plate
Checkpoint before anaphase

Question 21

What is the APC checkpoint?

Answer 21

Anaphase-promoting complex
Promotes degradation of cyclins which inactivated cdks. This triggers entry into anaphase

Question 22

What occurs during anaphase?

Answer 22

Sister chromatids separate and are moved toward opposite poles by microtubules
Normally all together, but sometimes chromosomes can lag

Question 23

What occurs during telophase?

Answer 23

Nuclear envelopes form and chromatids decondense

Question 24

What occurs during cytokinesis?

Answer 24

Actin contracts creating furrow which breaks off into two separate daughter cells

Question 25

How do cells detect DNA damage?

Answer 25

ATM/ATR kinase binds to DNA damages
Induce p53 and p21 to inactivate cdc

Question 26

What is the response to DNA damage?

Answer 26

Cell cycle arrest
DNA repair
Cell death