replication of DNA

Question 1

what does the nucleotide sequence of DNA encode

Answer 1

the primary structure of all cellular RNAs and proteins (including enzymes)

Question 2

what is replication

Answer 2

the process by which the DNA code is copied

Question 3

where does DNA replication occur

Answer 3

at an origin rich in A-T base pairings

Question 4

what happens to the parental strands at the start of dna replication

Answer 4

simultaneously unwound and replicated at replication forks

Question 5

what direction does DNA synthesis occur in

Answer 5

5/ to 3/ direction

Question 6

what is DNA synthesised by

Answer 6

DNA polymerases

Question 7

explain how DNA is synthesised by DNA polymers

Answer 7

3/-hydroxyl group of nucleotide on 3/-end of growing nucleic acid forms phosphodiester bond with 5/-a-phosphorus of the incoming deoxyribonucleoside 5/-triphosphate

Question 8

what does DNA polymerase require to start synthesis

Answer 8

primer segment

Question 9

what is a primer

Answer 9

often an oligonucleotide of RNA and removed once replication is completed

Question 10

intrinsic to all polymerases is what

Answer 10

a separate 3/ to 5/ exonuclease activity

Question 11

what does the 3/ to 5/ exonuclease activity do

Answer 11

double checks that the last nucleotide added to the growing chain is correct before DNA polymerase can proceed to the next template base

Question 12

what does helicases do

Answer 12

separates two parental strands by breaking hydrogen bonds using energy derived from ATP

Question 13

what does topoisomerase do

Answer 13

relives stress on double helix structure created by separation of 2 strands

Question 14

what do DNA binding proteins do

Answer 14

stabilize the separated strands

Question 15

what do primases do

Answer 15

synthesize primer strand which polymerase binds to in initiation of DNA synthesis

Question 16

what do polymerases do

Answer 16

synthesize DNA

Question 17

what are and what do exonucleases do

Answer 17

integral parts of polymerase protein
double checks insertion of bases

Question 18

why are DNA ligases used

Answer 18

at the end of replication, primer is removed, leaving a phosphodiester nick in DNA. ligases repair this break

Question 19

how many stages of DNA replication are there

Answer 19

3

Question 20

what are the 3 stages of DNA replication called

Answer 20

initiation, elongation and termination

Question 21

what happens during the initiation stage

Answer 21

helicases open the DNA helix at a replicating origin - an area rich in A-T base pairings, called autonomously replicating sequences

Question 22

what happens during elongation

Answer 22

the leading strand synthesis occurs continuously in the 5/ to 3/ direction
begings with the synthesis of an RNA primer by the primase at the replication origin
deoxyribonucleotides are added to the primer by polymerase, keeping pace with the unwinding of DNA at the replication fork

Question 23

what happens during the synthesis of the lagging strand

Answer 23

accomplished in short okazaki fragments which are then joined together by the action of liagse
DNA ligase catalyses formation of phosphodiester bonds between a 3/ hydroxyl at the end of one DNA strand and a 5/-phosphate at the end of another strand

Question 24

what happens during the termination stage

Answer 24

replication fork reaches a termination sequence and the process ends