Lecture 10- Rb and the cell cycle

Question 1

1) Summarize each step of the cell cycle, as well, name 4 classic checkpoints in the cell cycle.

Answer 1

-G1= cell’s cytoplasm and organelle are increasing, cell is growing, getting bigger, intakes lots of nutrients
- S= DNA duplication
- G2= making sure DNA is duplicated properly, we have enough organelle for two cells, getting ready for mitosis. Cell doesn’t really function properly in this phase
Checkpoints at= end of G1 to check for DNA damage, at S to make sure duplication is done properly, at G2 once again makes sure there isn’t an error in the DNA, and in mitosis, during metaphase it checks to see the chromosomes are lined up properly for segregation.

Question 2

2) What is Rad17, Bub and ATR protein kinase and what results in it being knocked out? In which checkpoint are they at?

Answer 2

• Rad17= and G2/M C.P and will result in multiple duplications of the DNA
• Bub= Anaphase, leads to nondisjunction
• ATR= S phase, loss of replication fork, pieces of DNA lost.

Question 3

3) What is the R-point in the cell cycle? Where is it in the cycle? Why is the R-point so crucial and so important to be regulated?

Answer 3

• Called the restriction point, it is near the end of the G1 phase. It is so crucial, because after this point the cell has committed to proliferation, if there is anything wrong with it, like being too big, or not mature yet, it will proliferate anyways

Question 4

4) What are some additional cell cycle checkpoints that may also halt the cycle?

Answer 4

• if nutrients is too low, it may cause apoptosis
• loss of connection to ECM (anoikis)
• DNA or physical damage apoptosis.

Question 5

5) What are CDKs and how are they activated? Which cyclins bind to which type of kinase protein and in what stage of the cell cycle do each peak at?

Answer 5

• cyclin dependant kinases are activated by regulatory molecules called cyclin
• G1= Kinase 4/6 binds to cyclin D
• After the R-point of G1= kinase 2 with cyclin E
• In S phase= kinase 2 with cyclin A
• Near the end of S phase, beginning of G2 kinase 1 with cyclin A
• in M phase, kinase 1 with cyclin B

Question 6

6) In what way are the D-cyclins different from the others? What is their main function? Name a few signaling pathways that effect cyclin D1.

Answer 6

Their levels fluctuate a lot, they don’t have huge peaks

• it is because they are influenced by extracellular signals and they main job is the convey those signals to the cell cycle clock in the nucleus. These cyclins are responsible for cells passing the R-point.
• Effected by Wnt, Ras, Patch-smooth, etc. Proliferation signals.

Question 7

7) How is the cyclin cycle controlled? What stimulates it and give examples of what inhibits it.

Answer 7

• the cycle is stimulated by the previous complexes, ie: D cyclin and kinase 4/6 stimulate E cyclin and kinase 2.
• Inhibition:
• INK4 proteins (p16, p18, p15, p19) target CDK 4/6 and prevent ATP binding to it and don’t allow the D-CDK 4/6 complex to form
• P57, p27 and p21 inhibit cyclins E, A, and B to their kinases.
• TGF-Beta can induce the binding of p15 to D-CDK 4/6 to prevent the complex from forming.

Question 8

8) How can the cyclin inhibitors become inhibited?

Answer 8

• Signals from mitogens may go through the PI3K pathway (Ras) and activated AKT/PKB which will phosphorelate P21 molecules in the nucleus and cause it to move towards the nuclear membrane,in the cytoplasm, ultimately diminishing it’s function to inhibit cyclin A, B and E from forming.

Question 9

9) What is the effect of P21 on D-cyclin complexes?

Answer 9

• they stimulate the formation of the complex.

Question 10

10) Discuss the relative concentrations of p27 and p21 cyclin inhibitors in the early, mid and late levels of G1 phase.

Answer 10

• at early levels the concentration of p27 and p21 are high …. Do it later