Topic 3-1 Flashcards
all DNA replication needs to be:
accurate and fast!
what were the three proposed models of DNA replication?
- conservative replication
- dispersive replication
- semiconservative replication
Meselson and Stahl’s experiment found that the true model for DNA replication is:
semi-conservative
what was Meselson and Stahl’s experiment?
- E.coli were grown in an 15N media first, and then were transferred to a 14N media and were allowed to replicate
- DNA from the 15N media appeared as a single, blue band; DNA from the first 14N generation were a single, purple band; DNA from the second 14N generation had a purple band and a red band
what are the four major steps of DNA replication (in prokaryotes)?
1) initiation
2) unwinding
3) elongation
4) termination
do prokaryotes have circular or linear DNA?
mostly circular
describe the initiation step of DNA replication (prok)
the origin of replication (OriC) is recognized by the initiator complex, which causes a slight unwinding of the DNA
what is the OriC?
a specific sequence of DNA that is recognized by the initiatior complex in DNA replication
needs single stranded DNA to do its job (needs the initiator complex to open a bubble)
DNA helicase
- prevents damage to ssDNA
- prevents secondary DNA structures
- sequence independent
these are characteristics of:
single stranded binding proteins (SSBs)
relieves torsion by cutting dsDNA during the unwinding phase of replication
DNA gyrase
DNA polymerase can only attach nucleotides to:
a pre-existing 3’OH group
DNA synthesis occurs in what direction?
5’ –> 3’
How does DNA polymerase start DNA synthesis?
it can’t, a primase is needed
what is the function of a primase?
it adds RNA primers (10-12 nucleotides long) to the ssDNA and leaves a 3’OH open for DNA polymerase to attach to
- large muliportein complex
- synthesizes DNA strand in 5’ to 3’ direction
- has 3’ to 5’ exonuclease activity to correct errors
- high processivity
these are all traits of:
DNA polymerase III
- large multiprotein complex
- synthesizes DNA in 5’ to 3’ direction
- removes RNA primers and replaces them with nucleotides
- low processivity
these are all traits of:
DNA polymerase I
what is the function of DNA ligase?
joins the okazaki fragments together to make a continuous strand of DNA
in prokaryotes, DNA replication ends when:
the two replication forks meet
some organisms contain a specific _________ that stops DNA replication
termination sequence
what is the alleged function of topoisomerase in theta replication?
they temporarily cleave the DNA
what are the two main types of circular DNA replication?
theta replication and rolling-circle replication
the base pair error rate is _______ mistakes/ 1 billion base paris
<1
how is the accuracy of DNA replication acheived?
1) errors in base pair selection by DNA polymerase = 1/100,000
2) proofreading by DNA polymerase
3) mismatch repai occurs soon after DNA replication
