DNA replication #10

Question 1

Aim of Meselson Stahl experiment

Answer 1

to determine DNA replication model

Question 2

what are the 3 postulated methods of replication?

Answer 2

~semi-conservative
~conservative
~dispersive

Question 3

Buoyant Density Centrifugation

Answer 3

allowed us to differentiate the parental(N15) and newly synthesized(N14) DNA by their different densities

Question 4

the replication forks are located

Answer 4

at the origins of replication

Question 5

Replicon

Answer 5

is a region of DNA that comes from a single origin of replication

Question 6

how is bacterial chromosome replicated?

Answer 6

bidirectional, as a single unit (is 1 replicon)

Question 7

what 2 genomic sequences mediate DNA replication

Answer 7

~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

Question 8

what 2 steps must happen in eukaryotes to start DNA replication?

Answer 8

the replicator selection and the origin activation

Question 9

DNA helicase function

Answer 9

binds to one of the strands of DNA and uses the energy from ATP hydrolysis to move along DNA

Question 10

Single Stand Binding Protein

Answer 10

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

Question 11

DNA synthesis cannot start without a

Answer 11

primer

Question 12

how does DNA synthesis start?

Answer 12

it always starts with an RNA primer - which is synthesized by DNA primase in prokaryotes and by DNApolalpha/primase in eukaryotes

Question 13

what is the direction of DNA synthesis

Answer 13

5’-3’

Question 14

length of okazaki fragments

Answer 14

1000-2000 nt in prokaryotes

100-400 nt in eukaryotes

Question 15

what is the primary enzyme used in DNA replication

Answer 15

DNA pol III

Question 16

processivity of an enzyme

Answer 16

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

Question 17

what is the sliding clamp?

Answer 17

the proliferating cell nuclear antigen is a trimer of proteins with 2 domains (prokaryotes have 3)

Question 18

how can the synthesis of the 2 strands happen in a synchronized fashion, in prokaryotes

Answer 18

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

Question 19

the trombone model

Answer 19

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

Question 20

primer

Answer 20

the template complex with the sliding clamp binds the DNA pol that starts the synthesis of a new okazaki fragment