3: Genome Maintenance- DNA Replication And Repair

Question 1

DNA Replication Enzymology

Answer 1

DNA polymerase (needs RNA primer), DNA ligase, RNA primer, DNA primase, Okazaki Fragment, Sliding clamp (helps polymerase stay on), Helicase (advance fork), Single-strand Binding Proteins, Topoisomerase (relieves supercoils).

Question 2

Trombone Slide Model

Answer 2

Leading and Lagging Strands are Replicated Together

Both are happening at replication fork

Question 3

Irinotecan

Answer 3

Inhibitor of Toposiomerase (used in cancer chemotherapy)

Question 4

Sliding Clamp (DNA replication)

Answer 4

Brace is called replication factor C (RFC)

Clamp is called proliferating cell nuclear antigen (PCNA)

Damage activates p53, turns on p21, binds and inactivates PCNA (inhibiting replication)

Question 5

Prokaryotic DNA Replication (origin)

Answer 5

Bi-directional from single origin site

Question 6

Eukaryotic DNA Replication (origin)

Answer 6

Bi-directional from multiple origin sites

Question 7

DNA Replication Origin

Answer 7

Origin of replication complex (ORC)
Binds to origin along with regulatory protein Cdc6 (prevents initiation)

MCM helicase joins ORC to open up DNA once Cdc6 inactivated

Question 8

Telomerase

Answer 8

Incomplete DNA 5’ end replication on lagging strand

DNA leaves 3’ overhangs at end

*RNA component for template and polymerase components

High telomerase levels in embryos and cancer cells

Question 9

DNA Replication (what can go wrong)

Answer 9

Fork can break (protein comes along and marks it, fixing system comes to fix it)

DNA polymerase puts in wrong base (proofreading and mismatch repair help)

DNA slippage- trinucleotide repeat expansions (Huntington Disease)
-can’t read it and passes over it, generating repeats.

Question 10

DNA Slippage

Answer 10

Generate repeats and contractions

Trinucleotide repeat expansions (Huntington Disease)

Polymerase cannot read and slips over it

Question 11

DNA Mismatch Repair

Answer 11

System scans for mismatch, parental or daughter strand

Bacteria: methylation clarifies

Humans: enzymes sense strands with gaps (because of origin sites all over)

Question 12

Hereditary Non-Polyposis Colon Cancer (Lynch Syndrome)

Answer 12

Few Polyps

Occurs after 40 years

5% colon cancers

Inherited mutations in Mismatch Repair (MSH2 or 6, MLH1, PMS2)

Look at CA micro satellite repeats stability (increases or decreases in tumor tissue)

Question 13

Familial Adenomatous Polyposis (FAP)

Answer 13

Many polyps

Young age

1% of colon cancers

Inherited mutations in FAP tumor suppressor gene

Remove colon (too many polyps)