DNA Replication and Recombination (Exam 3)

what are the 3 modes of DNA replication? describe each. Which one did Watson and crick say was the most likely scenario?

- Conservative: 1 new + 1 new = 1 strand

- Semi-Conservative: each strand is 1/2 old and 1/2 new. (This is most likely)

- Dispersive: The 2 new strands are mixes of old and new

where does replication begin? what direction does it proceed?

ORI (or ORIc in bacteria). It is bidirectional and goes both ways.

what is a replicon?

a unit of length to measure replicated DNA

Describe bacterial replication

- Single, circular DNA

- ORIc (only spot)

- more simple due to less DNA

What 4 things are required for DNA replication?

- DNA Poly 1

- DNA template

- A primer

- All 4 dNTPs

Describe chain elongation.

- Occurs in 5' to 3' direction by adding one nucleotide at a time to 3' end

- 5' carbon connects to PO4 and 3' of other carbon connects to other end of PO4

what is the role of DNA poly I, II, and III? which one is the only one capable of doing exonuclease activity from 5-3?

- Create/elongate DNA (all need primers)

- Only DNA poly I

What is the role of DNA poly I, II, IV, and V?

DNA repair

What are the 7 key issues to be resolved during DNA replication?

1. Unwind helix

2. reduce supercoiling

3. primers

4. lagging strand

5. remove RNA primers

6. Join primer gaps

7. proof reading

what does DNAa do?

binds to ORI and begin to open

Describe DNA helicase and its job.

Enters the hole made by DNA and opens DNA to recruit holoenzyme

what do SSBPs do?

stabilizes strand and prevents rebinding (holds open the "Door")

what is the role of DNA gyrase and topoisomerase?

gyrase: relieves supercoiling

topoisomerase: cut DNA

what are Okazaki fragments?

- fragments created by lagging strand

- need to remove primers and ligate gaps

what does DNA poly I do to primers? what does DNA ligase do after that?

It removes them and ligase glues the "holes" to create 1 strand

describe DNAs ability to proofread and do error corrections.

Not perfect. DNA poly exo 3'-5' to remove errors and prevent mutations

How is Eukaryal DNA synthesis different than bacterial?

- more complex

- many ORI's

- have a pre-RC to tag ORI as initiation spot

- have DNA poly alpha, epsilon, and delta