The Cell Cycle & Regulation

Question 1

Cell Cycle Phases (explain each)

Answer 1

Interphase

- G0 - dormant state, non cycling
- G1 - between end of division and DNA replication for growth
- S - DNA synthesis 
- G2 - between DNA replication and division

Division (M) - mitosis

Question 2

Cell Division (M phase)

Answer 2

prophase, prometaphase, metaphase, anaphase, telophase

Question 3

prophase

Answer 3

pt 1 of m phase

mitotic spindle forms

Question 4

pro metaphase

Answer 4

pt 2 of m phase

nuclear envelope is gone, microtubules attach to chromosomes

Question 5

metaphase

Answer 5

pt 3 of m phase

chromosomes aligned on mitotic spindle and attach

Question 6

anaphase

Answer 6

pt 4 of m phase

sister chromatids pulled apart by m. spindle

Question 7

telophase

Answer 7

final part of m phase

nuclear membrane reforms around new sets of chromosomes

Question 8

What is Progression, Transition and Checkpoint

Answer 8

Progression - moving through cell cycle phase
Transition - one phase to another
-Checkpoints - cell mechanisms that control order/timing of cell cycle phase transitions to make sure DNA is correct before reproduction

Question 9

How can we detect cell cycle phases

Answer 9

• Cells labeled with DNA-binding fluorescent dye
• Passed through cytometer
• Flurescence proportional to DNA content
• On histogram, two peaks shows G1 and G2/M phases, when Dan is highest; S is in between

Question 10

Cell cycle regulators

Answer 10

1) Cyclins

2) Cyclin Dependent Kinases (CDKs)

Question 11

Cyclins

Answer 11

• Cell cycle regulatory proteins
• 12 types
• Present during G1, S and G2/M phases

Question 12

Cyclin-Dependent Kinases (CDKs)

Answer 12

• Serine/Threonine kinanses

- Dependent on cyclin concentration for activation

Question 13

Cyclin and CDK pairings

Answer 13

-CDK4/CDK6 —— Cyclin D
-CDK2 ——— Cyclin E & Cyclin A
CDK1 ———– Cyclin A & B

Question 14

How do cyclins activate CDKs and act on a substrate

Answer 14

1) Cyclin binds to CDK
2) CDK-activating kinase (CAK) phosphorylates CDK’s threonine residue (PSTAIRE a-helix) while Cdc25 dephsphorylates inhibitory phosphates.
3) Cyclin-CDK complex phosphorylates substrate proteins, changing activation status.
4) Change in reg protein dictates whether next phase begins

Question 15

CDK4/CDK6 & Cyclin D Function and Dominant Activity

Answer 15

• Moves phase past restriction point at G1/S boundary

- Active during G1

Question 16

CDK2 and Cyclin A/E Function and Dominant Activity

Answer 16

• Initiates DNA synthesis is S phase
• Cyclin A: active during S1
• Cyclin E: active during G1/S transition

Question 17

CDK1 & Cyclin A/B Function and Dominant Activity

Answer 17

• Transition from G2 to M
• Cyclin A: active during S
• Clyclin B: active during G2

Question 18

What does ubiquitin do

Answer 18

Targets cyclin for destruction via proteasome

Question 19

What is responsible for Cyclin-CDK binding?

Answer 19

PSTAIRE alpha-Helix

Question 20

What is Cdc25

Answer 20

A protein phosphatase that activates Cyclin-CDK complex and remove inhibitory phosphates

Question 21

What is the order of cell phases?

Answer 21

G1, S, G2, M

Question 22

What are CKIs and the relevant types?

Answer 22

Cyclin-dependent kinase inhibitor

• INK4: p16^Ink4a
• CKI: p27^Kip1
• CKI: p21Cip1/Waf1

Question 23

CKI: p21 —- Cdk substrates and functions

Answer 23

• Most cdk-cyclin complexes
• Function:
  1) Induced by p53 tumor suppressor
  2) Stops cycle after DNA damage
  3) Cycle stop at senescence

Question 24

CKI: p57 —– Cdk substrates and Functions

Answer 24

• Most Cdk complexes
• Function:
  
  • growth suppressors will make it stop the cycle

Question 25

INK4: p16 —— cdk substrates and functions

Answer 25

• Cdk4, Cdk6
• Function:
  
  • cycle arrest in senescene
  • Works with retinoblastoma protein in growth regulation (pRb)

Question 26

Ras proteins (and mutation implication

Answer 26

• aka “small G proteins”
• Extracellular proteins/ligand (mitogen, which controls growth) binds to Ras protein, which in turn starts signal cascade to mic (transcription factor) to begin cell proliferation
• Mutation leads to Ras indicating cell to keep dividing (i.e. cancer)

Question 27

Myc transcription factor

Answer 27

protein signaled by Ras to activate/upregulate CDK and cyclin movement to begin cell proliferation

Question 28

Restriction point

Answer 28

point where cells commit to divide —- all or nothing

Question 29

Briefly describe the steps that drive the G1/S transition

Answer 29

1) D-CDK4 phosphorylates pRb
2) E-CDK2 hyperphosphorylates pRb, leading E2F1 to increase the creation of more cyclin E.
3) E-CDK2 creation is therefore increased, driving additional phosphorylations of pRb

Question 30

Briefly describe the steps that drive the G2/M transition

Answer 30

1) B-CDK1 activated and maintained by Cdc25
2) B-CDK1 move to the nucleus, begin spindle assembly
3) Once complete, Anaphase promoting complex (APC) destroys CDK1 to stop process

Question 31

Name the G1 checkpoints, give brief detail and under what conditions do they occur

Answer 31

• Done after DNA damage
  1) Slow - Stabilization p53, upregulation of p21, which binds and inhibits Cyclin-CDK complexes
  2) Fast - Activation of Chk2/Deactivation of Cdc25. Therefore Cdc25 can’t remove inhibitory phosphates.
  3) ARP/p16 pathway - G1 stops via 1) upregulation of p53 and p21, inhibiting CDK2 or 2) p16 will directly inhibit CDK4 & CDK6 kinases. BOTH PREVENT Rb Physphorylation.

Question 32

Explain the G2 checkpoints

Answer 32

1) DNA damage signals two ATM-dependent paths.
2) First path - Chk1/Chk2 target Cdc25 for export, leading to inactive B-CDK1 complex
3) Second path - p53 upregulates p21, which further inhibits B-CDK1

This results in G2 stop

Question 33

When does the cell cycle need to stop? What if it continued?

Answer 33

1) development
2) repair
3) tissue renewal

Pathology development