The Cell Cycle & Regulation Flashcards
Cell Cycle Phases (explain each)
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
Cell Division (M phase)
prophase, prometaphase, metaphase, anaphase, telophase
prophase
pt 1 of m phase
mitotic spindle forms
pro metaphase
pt 2 of m phase
nuclear envelope is gone, microtubules attach to chromosomes
metaphase
pt 3 of m phase
chromosomes aligned on mitotic spindle and attach
anaphase
pt 4 of m phase
sister chromatids pulled apart by m. spindle
telophase
final part of m phase
nuclear membrane reforms around new sets of chromosomes
What is Progression, Transition and Checkpoint
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
How can we detect cell cycle phases
- 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
Cell cycle regulators
1) Cyclins
2) Cyclin Dependent Kinases (CDKs)
Cyclins
- Cell cycle regulatory proteins
- 12 types
- Present during G1, S and G2/M phases
Cyclin-Dependent Kinases (CDKs)
- Serine/Threonine kinanses
- Dependent on cyclin concentration for activation
Cyclin and CDK pairings
-CDK4/CDK6 —— Cyclin D
-CDK2 ——— Cyclin E & Cyclin A
CDK1 ———– Cyclin A & B
How do cyclins activate CDKs and act on a substrate
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
CDK4/CDK6 & Cyclin D Function and Dominant Activity
- Moves phase past restriction point at G1/S boundary
- Active during G1
CDK2 and Cyclin A/E Function and Dominant Activity
- Initiates DNA synthesis is S phase
- Cyclin A: active during S1
- Cyclin E: active during G1/S transition
CDK1 & Cyclin A/B Function and Dominant Activity
- Transition from G2 to M
- Cyclin A: active during S
- Clyclin B: active during G2
What does ubiquitin do
Targets cyclin for destruction via proteasome
What is responsible for Cyclin-CDK binding?
PSTAIRE alpha-Helix
What is Cdc25
A protein phosphatase that activates Cyclin-CDK complex and remove inhibitory phosphates
What is the order of cell phases?
G1, S, G2, M
What are CKIs and the relevant types?
Cyclin-dependent kinase inhibitor
- INK4: p16^Ink4a
- CKI: p27^Kip1
- CKI: p21Cip1/Waf1
CKI: p21 —- Cdk substrates and functions
- Most cdk-cyclin complexes
- Function:
1) Induced by p53 tumor suppressor
2) Stops cycle after DNA damage
3) Cycle stop at senescence
CKI: p57 —– Cdk substrates and Functions
- Most Cdk complexes
- Function:
- growth suppressors will make it stop the cycle
INK4: p16 —— cdk substrates and functions
- Cdk4, Cdk6
- Function:
- cycle arrest in senescene
- Works with retinoblastoma protein in growth regulation (pRb)
Ras proteins (and mutation implication
- 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)
Myc transcription factor
protein signaled by Ras to activate/upregulate CDK and cyclin movement to begin cell proliferation
Restriction point
point where cells commit to divide —- all or nothing
Briefly describe the steps that drive the G1/S transition
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
Briefly describe the steps that drive the G2/M transition
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
Name the G1 checkpoints, give brief detail and under what conditions do they occur
- 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.
Explain the G2 checkpoints
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
When does the cell cycle need to stop? What if it continued?
1) development
2) repair
3) tissue renewal
Pathology development
