Cell Cycle from Rich Notes

Question 1

The Eukaryotic cell cycle is divided into what 4 phases?

Answer 1

G1, S, G2, and M

Question 2

What phase of the cell cycle is the growth phase in which cells are metabolically active?

Answer 2

G1

Question 3

What phase of the cell cycle is the phase where DNA is replicated?

Answer 3

S

Question 4

What phase of the cell cycle is the second growth phase during which the cell prepares for mitosis?

Answer 4

G2

Question 5

What phase of the cell cycle is where the chromosomes are segregated and the cell divides into two daughter cells?

Answer 5

M

Question 6

Which divides faster, yeast or mammalian cells?

Answer 6

Yeast. (90 min vs. 18-24 hours)

Question 7

During the early divisions of embryonic cells, the G1 and G2 phases are actually skipped. What happens as a result, and how is it possible to do this?

Answer 7

Blastomeres become smaller.

Oocytes store a lot of maternally transcribed RNAs and proteins that the first few cells use.

Question 8

What is the point in G1 for yeast where they check to see if the conditions are right to proceed to the S phase? What controls whether or not the yeast pass this point?

Answer 8

START

external factors like nutrients and mating factors

Question 9

What point in the G1 phase for animal cells do the cells check to see if conditions are right to go into the S phase? What allows the cells to pass this point?

Answer 9

restriction point

external growth factors - without these, the cell enters G0. cell metabolically active, but doesn’t divide.

Question 10

DNA is replicated once during the cell cycle. This is step is regulated by what of the ORC and by binding of the what to replication origins?

Answer 10

phosphorylation; MCM helicase

Both of these prevent replication origins of being used again until cell cycle complete.

Question 11

What is the function of external signals in the cell cycle? Internal signals?

Answer 11

E: coordinate cell division w/ conditions in the cells environment

I: process goes in proper order, one phase completes before another starts, and no errors at any steps

Question 12

What are examples of external signals in the cell cycle? Internal signals?

Answer 12

E: nutrients or growth factors

I: signaling cascades started by growth factors, and cyclins and cyclin-dependent kinases

Question 13

What is MPF, maturation promoting factor, made of?

Answer 13

Cyclin B and Cdk1

Question 14

In a general sense, how is Cdk1 regulated?

Answer 14

by association with Cyclin B and by phosphorylation and dephosphorylation of specific amino acids on the Cdk

Question 15

In a specific, crazy long flow chart sense, how is Cdk1 regulated?

Answer 15

Cdk activating kinase adds phosphate (P) to Thr 161 and kinase wee1 adds P to Tyr 15 on Cdk1, Cdk1 is inhibited by P on Tyr 15; when proper stimulus received, phosphatase cdc25 removes P at Tyr 15 –> activates MPF (complex) –> adds P to targets; Cyclin B destroyed by proteasome later and Cdk1 inactivated; removal of P at Thr 161 further inactivates Cdk1

Question 16

Match each Cdk with the correct cyclin and cell cycle phase. Each should only be used once. There are 5 combinations.
Cdk: 1, 1, 2, 2, 4/6
Cyclin: A, A, B, D, E
Early G1-R, G1 to S transition, S, S to G2 transition, G2 to M transition

Answer 16

Cdk 4/6, Cyclin D, Early G1-R
Cdk 2, Cyclin E, G1 to S transition
Cdk 2, Cyclin A, S
Cdk 1, Cyclin A, S to G2 transition
Cdk 1, Cyclin B, G2 to M transition

Question 17

What are the two families of Cdk inhibitors, what members make up each family, and what does each family bind to?

Answer 17

Ink4; p15, p16, p18, p19; Cdk4/6 (inhibits progression through G1)

CIP/KIP; p21, p27, p57; Cdk2/Cyclin A or Cdk2/Cyclin E (inhibits progression through G1 and S phases)

Question 18

Growth factor signaling activates a signaling cascade through Ras/Raf/MEK/ERK that promotes the synthesis of which cyclin during G1?

Answer 18

Cyclin D

Question 19

What is an example of a protein that is phosphorylated by

Cdk4,6/Cyclin D?

Answer 19

Retinoblastoma or Rb

Question 20

The Rb protein regulates the transcription of what cyclin? How does it do this?

Answer 20

Cyclin E; binds to E2F in hypophosphorylated state, transcription repressed; Rb phosphorylated by Cdk4,6/Cyclin D
–> Rb dissociates –> transcription enhanced

Question 21

Early in G1, Cdk2/Cyclin E is inhibited by p27. How is this inhibition relieved?

Answer 21

Increased synthesis of Cyclin E, and inactivation of p27 by its binding to Cdk 4,6/Cyclin D and its degradation; activation of Cdk2/Cyclin E allows cell to pass R and make transition from G1 to S phase

Question 22

Where are the checkpoints in the cell cycle to check for DNA damage or incompletely replicated DNA? What happens if the damage cannot be repaired?

Answer 22

G1, S, G2; apoptosis

Question 23

In M phase, a checkpoint ensures that the chromosomes are properly aligned so that they can be distributed equally to the two daughter cells. What is this checkpoint called?

Answer 23

spindle assembly checkpoint

Question 24

Damaged DNA is detected by complexes that contain either ATM or ATR. What does ATM recognize? (No, not a debit card…) What does ATR recognize?

Answer 24

ATM: double strand breaks

ATR: single strand breaks or unreplicated DNA

Question 25

Both ATM and ATR are kinases that phosphorylate downstream kinases Chk1 or Chk2. What do Chk1 and Chk2 do?

(Did a banker discover this stuff? ATM, Chk looks like Check……..)

Answer 25

phosphorylate cdc25 phosphatase, which prevents it from activating Cdk1 and Cdk2 by removing inhibitory phosphate at Tyr 15

Question 26

ATM and Chk2 also phosphorylate transcription factor p53. What does p53 do? What kinds of cells is p53 often mutated in?

Answer 26

increases the synthesis of p21, which inhibits Cdk2/Cyclin E and prevents the cell from entering S phase

tumor cells

Question 27

How many daughter cells are produced from cellular replication?

Answer 27

Two