Mitosis & Cell Cycle

Question 0

How does CDK/cyclin do to RB?

Answer 0

Inhibits it.

Question 1

What does RB (retino-blastoma) do?

Answer 1

Inhibits the cell cycle. Keeps it in G1

Question 2

What are the two families of cdk inhibitors?

Answer 2

Ink4 (p16, for instance)

Cip/Kip (p21, for instance)

Question 3

What does the ORC (origin recognition complex) do?

Answer 3

recognizes and binds to the dna replication origin

Question 4

What proteins make up the Pre-Replication Complex (Pre-RC)?

Answer 4

Orc 1-6
Cdt1, Cdc6
DNA helicase (Mcm 2-7)

Question 5

When is the Pre-RC formed?

Answer 5

During G1

Orc binds (marks) the origin.
Other factors see Orc and bind to it.
helicase comes in
It waits…

Question 6

What is the regulated step that allows replication to move forward?

Answer 6

Activation of the helicase in the Pre-RC and simultaneous binding of the other replication factors.

Pre-RC formation is NOT regulated.

Question 7

What is the Pre-RC cycle?

Answer 7

1. Building of the Pre-RC in G1 (no activation allowed)
2. Activation of the Pre-RC as you go into S phase (no Pre-RC building allowed)
3. Continue blocking Pre-RC building the rest of the cell cycle till back at G1

Question 8

What regulates p21?

Answer 8

p53

Question 9

Explain how CDK gets turned on?

Answer 9

high cyclin concentration
cyclin binds to CDK
CDK-cyclin complex is phosphorylated by CAK (CDK-activating kinase)

Question 10

What are the amino acids that get phosphorylated by CDK’s (of varying flavors)? And where are they phosphorylated?

Answer 10

Phosphorylated at the -OH group

1. i. Serine -CH2-OH
   ii. Threonine -CH(OH)-CH3
2. Tyrosine -CH2-Ph-OH (para Ph)

Question 11

What do transducers (usually) do?

Answer 11

Phosphorylate other proteins (effectors) that actually “do” something.

Question 12

At what phase transitions can Effectors pause the cell cycle and fix DNA damage?

Answer 12

All of them…
G1 –> S
S –> G2
G2 –> M

Question 13

What does Rad17 do?

Answer 13

Detects radiation damage and stops the cell cycle. Recruits ATM/ATR

Question 14

What do ATM/ATR do?

Answer 14

ATM/ATR are transducers (kinases).
They phosphorylate Chk2/Chk1
Chk2/Chk1 phosphorylate effectors (such as p53 trxn factor for p21)

Question 15

How does p53 regulate p21?

Answer 15

If p53 is phosphorylated (by ATM/ATR), it does its job as trxn factor for p21.
p21 then inhibits CDK and the cell cycle is arrested (G1–>S or G2 –>M)

Question 16

What are some of the DNA damage categories that call on ATM/ATR?

Answer 16

Double strand breaks
Stalled Replication forks
DNA mismatches
Nucleotide damage

Question 17

What do Chk1/Chk2 do?

Answer 17

Chk1/Chk2 are a second layer of transducers; kinases (after ATM/ATR)

1. start the repair process
2. inhibit (Cdc25) CDK’s
3. phosphorylate p53 which sends for either apoptosis or p21

Question 18

If a cell (mammary) loses its good copy of BRCA2, so now only has defective BRCA2, what functionality has this cell lost?

Answer 18

Cell checkpoint pathway is no longer functional

Question 19

What happens in cells with only a mutant BRCA2?

Answer 19

DNA damage is not detected because checkpoints are lost.

More than the normal 2 copies of DNA in the S phase are seen.

Question 20

What is the really detrimental deletion in small cell lung cancer (as discussed in lecture)?

Answer 20

RB

So now there is no communication between the inside and outside of the cell (in regards to cell cycle regulation)
The cell cycle has nothing inhibiting it so division of tumor cells is very fast.

Question 21

What is the “double whammy” found in non-small cell lung cancer (as discussed in lecture)?

Answer 21

RB is present and active but over expression of cyclinD (unregulated)
p16 is not present so the over-expressed cyclinD will phosphorylate RB unchecked, and inactivate it.

Question 22

Why is it easer to treat non-small cell lung cancer if it has the “double whammy” ?

Answer 22

You can use drugs to block the phosphorylation of RB by cyclinD/Cdk4