lecture 3 & 4 - dna replication Flashcards
is dna replication semi-conservative or conservative
semi-conservative
what was discovered in 1953
Watson and Crick discovered that DNA is symmetrical (important idea for DNA rep)
explain the meselson-stahl experiment
proves that DNA rep is semi-conservative
E. coli (fast replicator) is grown in 15N which is rather heavy, then it was switched to 14N which is lighter. All the replications were the same weight in the first generation but in the second generation they started to be different weights which proves semi-conservative
where does replication begin in prokaryotes
in the middle of DNA in an A-T area
which direction along the DNA does replication move
bidirectional
who identified dna polymerase
arthur kornberg
what does DNA Pol III do in prokaryotes
catalyzes addition of nucleotide to growing DNA chain
what does DNA poly III require in prokaryotes
primer and template
which way does dna pol iii move in prokaryotes
5’ to 3’ with respect to growing chain (antiparallel to template)
what do the other dna polymerases do in prokaryotic replication
help with repair reactions
how do the leading and lagging strands differ in DNA rep
leading is synthesized continuously while lagging is made with short Okazaki fragments that are joined together afterwards
what is primase
a RNA polymerase in E coli that provides a priming end
what happens to the RNA left my primase once replication is complete in prokaryotic replication
the RNA primer is removed 5’ -> 3’ by exonuclease activity of DNA Pol I and then the gaps are filled in by DNA Pol I
do okazaki fragments require primers
yes
what does DNA ligase do in DNA replication
connects the 3’ end of one okazaki frag to 5’ end of the next
what makes up the DNA Pol III holoenzyme
900 kD dimeric structure
each monomeric unit has catalytic core, dimerisation subunit and a beta clamp. there is a single clamp loader complex
each core is associated with one strand of DNA. core has the polymerase and the 3’-5’ exonuclease
the clamp loader places the sliding clamp (beta complex) onto the DNA
what is a 3’-5’ exonuclease
proof reads to make sure the correct base was added
what is a single stranded binding protein
helps protext the single stranded dna to prevent from degradation and secondary structure formation
what does topoisomerase do in prokaryotes
prevents DNA from getting tangled (relieves pressure in supercoiled DNA)
what does helicase do in DNA replication
disrupt the h bonds that hold the 2 dna strands together
what makes up the replisome in dna replication
helicase + primosome + polymerase
how can the 2 DNA polymerases complexed be attached and move in opposite direction in DNA rep
the lagging strand is looped back
where does dna replication termination occur in prokaryotes
opposite oriC by contrahelicase
how many origins of replication are there in euk dna rep
multiple
