Mitosis and Cell Cycle

Question 1

List the stages of the somatic cell cycle and what occurs in each.

Answer 1

1. G1: (regulation) cell growth is coordinated with cell division at the restriction point R where the cell determines if it is big enough o move on to S phase
2. S: chromosome synthesis occurs
3. G2: (regulation)
4. M: chromosome segregation occurs

Question 2

What is the main goal of the somatic cell cycle?

Answer 2

To ensure exact duplication of the genome is S phase followed by exact division of the genome in M phase to produce identical daughter cells.

Question 3

How do cells prevent re-replication of their genomes?

Answer 3

By keeping the assembly and activation of replication complexes in separate cell cycle phases.

Question 4

What are the consequences of genomic instability either by chromosome re-replication in S phase or mis-segregation during mitosis?

Answer 4

Human diseases such as cancer and birth defects, like trisomy 21

Question 5

Why do differentiated, post-mitotic cells such as neurons grow without cycling?

Answer 5

Because they are stuck at the restriction point R

Question 6

Why are mutations in CDI genes a marker for cancer?

Answer 6

Active CDKs (cyclin dependent kinase) are produced by growth factor hormones/cancer factor proteins => cell replication
CDIs (CDK Inhibitors) turn off CDKs and mutations often affect ability to turn off CDKs => uncontrolled proliferation

Question 7

Which mutation is most frequently seen in cancer cells?

Answer 7

Mutation in Ink4 (CDK4 inhibitor)

=> lets CDK4 push past the restriction point regardless of other growth factors

Question 8

How is the presence of RB (retinoblastoma protein) indicative of cancer development?

Answer 8

RB is an S phase inhibiting, tumor suppressor:
Low [RB] or PO4’d RB => abnormally high replication rates

i.e. small lung cancer

Question 9

How do mitogens have a role in cancer development?

Answer 9

Mitogens signal activation of CDK4 which leads to the inhibition of RB and a positive feedback cycle => irreversible commitment to completing the cell cycle

Question 10

Why do patients that lack ATM (ataxia telangiectasia mutated) have a high risk of cancer?

Answer 10

ATM is an integral protein kinase for the DNA damage checkpoint

ATM is a serine/threonine protein kinase recited for double stranded DNA break repair; it PO4’s proteins (p53, CHK2, H2AX tumor suppressors) to activate cell cycle arrest, DNA repair or apoptosis