DNA replication #10 Flashcards
Aim of Meselson Stahl experiment
to determine DNA replication model
what are the 3 postulated methods of replication?
~semi-conservative
~conservative
~dispersive
Buoyant Density Centrifugation
allowed us to differentiate the parental(N15) and newly synthesized(N14) DNA by their different densities
the replication forks are located
at the origins of replication
Replicon
is a region of DNA that comes from a single origin of replication
how is bacterial chromosome replicated?
bidirectional, as a single unit (is 1 replicon)
what 2 genomic sequences mediate DNA replication
~replicator: is a set of in-cis- acting nucleotide sequences that can control replication. Includes easily denaturable DNA region
~initiator: protein that recognizes the replicator
what 2 steps must happen in eukaryotes to start DNA replication?
the replicator selection and the origin activation
DNA helicase function
binds to one of the strands of DNA and uses the energy from ATP hydrolysis to move along DNA
Single Stand Binding Protein
bind to exposed single stranded DNA without covering the bases. They help stabilize unbound DNA. They coat and straighten out the regions of single stranded DNA on the lagging strand
DNA synthesis cannot start without a
primer
how does DNA synthesis start?
it always starts with an RNA primer - which is synthesized by DNA primase in prokaryotes and by DNApolalpha/primase in eukaryotes
what is the direction of DNA synthesis
5’-3’
length of okazaki fragments
1000-2000 nt in prokaryotes
100-400 nt in eukaryotes
what is the primary enzyme used in DNA replication
DNA pol III
processivity of an enzyme
is its ability to catalyze consecutive reactions without releasing the substrate.
the # of nt added by the enzyme per association event with the template strand
what is the sliding clamp?
the proliferating cell nuclear antigen is a trimer of proteins with 2 domains (prokaryotes have 3)
how can the synthesis of the 2 strands happen in a synchronized fashion, in prokaryotes
they are synthesized at the same time to minimize exposure of ssDNA.
This is done by the fact that the 2 DNA polymerases are bound to each other at the growing fork linked together in the DNA pol III holoenzyme complex by a T-subunit dimer
the trombone model
is the replication model in prokaryotes.
the helicase unwinds the DNA
the leading strand is duplicated
the lagging strand is covered in SSBP
AT regular intervals, on the lagging stand a primer and an okazaki fragment are synthesized
the DNA sliding clamp is loaded on the newly formed template — primer junction on the lagging strand
primer
the template complex with the sliding clamp binds the DNA pol that starts the synthesis of a new okazaki fragment
