Lecture 13: DNA Replication Flashcards
In which phase of the cell cycle does DNA replication occur?
The S phase
Which DNA polymerase is involved in DNA replication? Function?
1 and 3
1: repair and recombination, also helps create the phosphate backbone, getting rid of primers in OKAZAKI
3: adds nucleotides to the synthesising strand (MAIN)
How many DNA polymerases does E.Coli have, and how many are actually involved in DNA replication?
5; only 2 involved
The growing strand: which way?
Bases added to the 3’ end: so grows 5’ to 3’
Why is RNA primer needed?
We need at least a small section of double strand to be able to begin DNA replication. RNA can spontaneously replicate itself whereas DNA cannot (needs primer)
Differences in Poly 1 and 3; size, subunits, processivity, speed
Size: Poly 3 > Poly 1
Subunits: Poly 3 > Poly 1
Processivity: Poly 3 > Poly 1
Speed: Poly 3 > Poly 1
What does “processivity” of polymerase mean?
The number of bases/things it can add on until it falls off; its limit
What is proofreading and what is the difference in proofreading of Poly 1 and 3?
Proofreading/EXONUCLEASE: removing nucleotides
BOTH can proofread 3’ to 5’ (backwards)
ONLY POLY 1 can proofread 5’ to 3’ (forwards)
Differences in origin of replication of EUK vs PRO?
Eukaryotes have MULTIPLE origins of replication
There is an important section in the DNA strand important for replication; what is it?
The section where there are multiple A-T base pairs. These bonds are weak and therefore this section is easy to separate, in preparation for replication.
What is a replication fork?
“The point at which DNA strands are separated to allow replication”. The area where replication actually takes place.
Name the proteins involved in INITIATION OF REPLICATION
- DNA A
- DNA B
- Primase
- Single-stranded DNA-binding protein
- DNA gyrase (topoisomerase)
Another name for DNA gyrase?
Topoisomerase 2
What is the function of DNA A?
Recognises the origin sequence, gets the whole process started
What is the function of DNA B?
Unwinds the DNA (one at each replication fork/end)’ i.e 2