L55 cell division

Question 1

CDK

Answer 1

cyclin dependant kinases

activity depeds in Cyclin
-cyclin determines specificity

phosphorylate serine threonine residies of substrate protiens

Question 2

Phase and cyclin

Answer 2

G1 early: D  4/6
G1 late: E   2
-dependant on external signaling by mitogens
G1S : A   2
SG2:   A 1 (CDC2)
G2/M  B    1 (CDC2)
-dependant on DNA rep completion
Mphase check
-dependant on alignment of chromosomes

Question 3

Cell cycle starts

Answer 3

Mitogen binds to RTK , phophorylationL via MAPK, synthesis of MYC
-myc drives expression go Cyclin D

C-CDK 4/6 first active compled
-must be exposed every time to mitogen

Question 4

restriction point

Answer 4

sequential activity of Cyclin D-4/6 followed by Cyclin E-CDK2 allow cell to pass rest point
both work in tandem to Pohphorylate a protein called Rb

Rb allows activation of E2f

RETINOBLASTOMA: Rb -tumor suppressor

• 3rd gest month
• hyperphosphorylation does not allow Rb to bind and suppress E2F so all protiens are expressed

1. GF signal increase synthesis of Cyclin D—CDK4/6
2. C-CDK 4/6 begins to phos serient threonine residoes (hypophosphorylation)
3. partioal active E2F allows production of Cyclin E—-CDK2
4. E-CDK2 HYPERphosphorylates and completes Rb inactivation

Question 5

M phase checkpoint

Answer 5

G2M and M phase have scheduled halts

G2-M: activation of CDK1
M and spindle: deactivation of CDK 1

MPF maturation promoting factor
-cdc2 (cell division cycle) –cyclin B complex is as a unit is called MPF

1. large number of B-CDC2 (MPF) complexes have been stockpiled but are not active
   - inacgtivating phophoylations of B—CDC2 during G2 ensures CDC2 activity is minimal until ready for mitosis

:ready signal”- dna synth complete, activation of CDC25-DEPHOSPHORYLATES MPF

Question 6

metaphase

Answer 6

line up X and spindle assembly checkpoint

-all cear signal

• activates APC (anaphase promoting complex)- ubiquitin ligase
• degrades Cyclin B & cohesion (what binds chromatids together)
• cohesion is the substrate for separase (usually kep in an inactive form via binding if inhibitory subunits)
• activated destruction of inhibitory unit of separase, degrades cohesion

Question 7

unexpected DNA damage

Answer 7

CDKi-can halt cell cycle at any phase damage is detected

INK4 group: inhibitor of CDK4 or 6

• P16 protein
• environmental stress

WAF1/CIP1 groupL inhibits all cyclin CDK’s except 4/6

• p21
• dna damage (involved p53)