Mitosis & Cell Cycle Flashcards
How does CDK/cyclin do to RB?
Inhibits it.
What does RB (retino-blastoma) do?
Inhibits the cell cycle. Keeps it in G1
What are the two families of cdk inhibitors?
Ink4 (p16, for instance)
Cip/Kip (p21, for instance)
What does the ORC (origin recognition complex) do?
recognizes and binds to the dna replication origin
What proteins make up the Pre-Replication Complex (Pre-RC)?
Orc 1-6
Cdt1, Cdc6
DNA helicase (Mcm 2-7)
When is the Pre-RC formed?
During G1
Orc binds (marks) the origin.
Other factors see Orc and bind to it.
helicase comes in
It waits…
What is the regulated step that allows replication to move forward?
Activation of the helicase in the Pre-RC and simultaneous binding of the other replication factors.
Pre-RC formation is NOT regulated.
What is the Pre-RC cycle?
- Building of the Pre-RC in G1 (no activation allowed)
- Activation of the Pre-RC as you go into S phase (no Pre-RC building allowed)
- Continue blocking Pre-RC building the rest of the cell cycle till back at G1
What regulates p21?
p53
Explain how CDK gets turned on?
high cyclin concentration
cyclin binds to CDK
CDK-cyclin complex is phosphorylated by CAK (CDK-activating kinase)
What are the amino acids that get phosphorylated by CDK’s (of varying flavors)? And where are they phosphorylated?
Phosphorylated at the -OH group
- i. Serine -CH2-OH
ii. Threonine -CH(OH)-CH3 - Tyrosine -CH2-Ph-OH (para Ph)
What do transducers (usually) do?
Phosphorylate other proteins (effectors) that actually “do” something.
At what phase transitions can Effectors pause the cell cycle and fix DNA damage?
All of them…
G1 –> S
S –> G2
G2 –> M
What does Rad17 do?
Detects radiation damage and stops the cell cycle. Recruits ATM/ATR
What do ATM/ATR do?
ATM/ATR are transducers (kinases).
They phosphorylate Chk2/Chk1
Chk2/Chk1 phosphorylate effectors (such as p53 trxn factor for p21)
How does p53 regulate p21?
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)
What are some of the DNA damage categories that call on ATM/ATR?
Double strand breaks
Stalled Replication forks
DNA mismatches
Nucleotide damage
What do Chk1/Chk2 do?
Chk1/Chk2 are a second layer of transducers; kinases (after ATM/ATR)
- start the repair process
- inhibit (Cdc25) CDK’s
- phosphorylate p53 which sends for either apoptosis or p21
If a cell (mammary) loses its good copy of BRCA2, so now only has defective BRCA2, what functionality has this cell lost?
Cell checkpoint pathway is no longer functional
What happens in cells with only a mutant BRCA2?
DNA damage is not detected because checkpoints are lost.
More than the normal 2 copies of DNA in the S phase are seen.
What is the really detrimental deletion in small cell lung cancer (as discussed in lecture)?
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.
What is the “double whammy” found in non-small cell lung cancer (as discussed in lecture)?
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.
Why is it easer to treat non-small cell lung cancer if it has the “double whammy” ?
You can use drugs to block the phosphorylation of RB by cyclinD/Cdk4
