Molecular basis of inheritance part 2 Flashcards
What does helicase do
unwinds dna strands at the replication fork by breaking H-bonds
What does DNA polymerase do (4)
- Synthesizes new DNA strand by adding nucleotides to free 3’-OH grp of pre-existing DNA strand or RNA primer
- Uses parental strand as template
- Makes DNA in 5’ –> 3’ direction (links 5’ phosphate grp of new nucleotide to 3’-OH of growing strand)
- Reads template strand from 3’–> 5’
What does topoisomerase do
Relieves “overwinding” ahead of replication fork
what does primase do (2)
- RNA polymerase that synthesizes an RNA primer complementary to the DNA strand
- Provides a 3’ end for DNA polymerase
What does ligase do (2)
- glues together nicks in DNA sugar-phosphate backbone (forms phosphodiester bond)
- needed after RNA primers are replaced by DNA and for Okazi fragments
What do single-stranded binding proteins do
stabilizes single stranded DNA
Circular double stranded DNA (like in E. coli cell) has how many origins of replication and how many replication bubbles
- 1 origin of replication
- 1 replication bubble
Linear double stranded DNA (eukaryotic cell) has __ origins of replication and ____ replication bubbles
- Many origins of replication (100s-1000s)
- Many replication bubbles
What is the first step of DNA replication
initiation
where does initiation begin
origins of replication, which are short specific sequences of DNA
What 3 proteins bind to the origin of replication during initiation
- helicases (unzipping of DNA)
- single stranded binding proteins (stabilizes ss DNA)
- topoisomerase (relieves strain of unwinding)
in a replication bubble, how many replication forks
2 (Y-shaped region)
What enzyme does elongation involve
DNA polymerase III
What is elongation in DNA replication (4)
- synthesizes new strand of DNA using parental strand as template
- adds nucleotides according to base pairing rules
- links nucleotides in growing DNA strand
- requires free 3’ OH grp
What end does DNA polymerase add nucleotides to
3’end of existing nucleotide => primer needed for synthesis
in what direction does synthesis occur
5’ to 3’ direction
DNA polymerase reads template in what direction
3’ to 5’ direction
template dna containing a 3’ to 5’ strand and a 5’ to 3’ strand means replication is…
bidirectional
in dna leading strand:
DNA polymerase III synthesizes dna in what direction
same direction as dna unwinding= 5’ to 3’ toward replication fork
in what direction is template read in leading strand ?
3’ to 5’
how many rna primers needed in leading strand
1
what is a lagging strand
from discontinuous dna synthesis
in what direction does dna polymerase III synthesize DNA for lagging strands
opposite direction of DNA unwinding (5’ to 3’ away from replication fork)
in what direction is the template read in lagging strands
3’ to 5’
