Lecture 2 Flashcards
1
Q
DNA replication
A
- cell contains full DNA complement (every division need replication of full genome)
- copying mechanism for genetic material
- two strands are complimentary; each acts as template for building new strand
- parent molecule unwinds/unzips; new strand constructed from free nucleotides using base-pairing rules
2
Q
Alternative models
A
- semiconservative: each daughter molecule comprises one strand for parent molecule
- conservative: two parent strands rejoin, newly made strands join
- dispersive: each stand is mix of old and new
3
Q
isotrpic tracing
A
- labelled nucleotides (supplied parents heavy isotrope of nitrogen; free nucleotides lighter isotrope)
- semiconservative correct
4
Q
Origins of replication
A
- begins at special sites called origins of replication (two strands separate opening replication ‘bubble’)
- replication proceeds for orifin until entire colecule is copied
5
Q
replication fork
A
- each replication bubble is a replication forke (y shaped region where new DNA strands elongate)
- dozen enzymes/other proteins participate in DNA replication
6
Q
untwisting helix
A
- helicase: enzyme that untwists and separates double helix at fork
- single-strand binding proteins: binds to stabilise single-strand DNA
- topoisemerase: corrects ‘overwinding’ ahead of forks by breaking, swivelling and rejoining DNA
7
Q
elongating new strand
A
- catalysed by polymerases
- DNA polymerases require primer and DNA template
- polymerases add nucleotides to free 3’ end of growing strand (new DNA strand can elongate only in 5’ -> 3’ direction)
- rate is about 500 nucleotides/s in bacteria; 50 for humans
8
Q
nucleotide addition
A
- added nucleotide is nucleoside triphosphate
- dATP supplies adenin to DNA (similar to ATP; difference is sugars)
- monomer of dATP joine strand; loses two phosphate groups as molecule of pyriphosphate
9
Q
antiparallel elongation
A
- leading strand
- along one template DNA polymerase synthesises leading strand continuously
- moving toward replication fork
- lagging strand
- polymerase 3 works in direction away from fork to elongate new strand
- lagging strand synthesised as seriesof segments (okazaki fragments) subsequently joined by ligase
- polymerase 1 replaces RNA primers with DNA
10
Q
DNA replication complex
A
- proteins participate in DNA replication (form large complex - DNA replication machine)
- replication machine probably stationary (reeling in parental DNA; extruding new daughter DNA)
11
Q
Bacterial DNA replication proteins
A
- helicase
- single-strand binding protein
- topoisomerase
- primase
- DNA pol 3
- DNA pol 1
- DNA ligase
12
Q
helicase
A
- unwinds helix
13
Q
SSBP
A
- binds to stabilise
14
Q
topo.
A
- relieves overwinding
- braking, swiveling, rejoining
15
Q
primase
A
- synthesises RNA prime at 5’ end (leading strand)
- and of each Ozaki fragment (lagging strand)
