replication of DNA Flashcards
what does the nucleotide sequence of DNA encode
the primary structure of all cellular RNAs and proteins (including enzymes)
what is replication
the process by which the DNA code is copied
where does DNA replication occur
at an origin rich in A-T base pairings
what happens to the parental strands at the start of dna replication
simultaneously unwound and replicated at replication forks
what direction does DNA synthesis occur in
5/ to 3/ direction
what is DNA synthesised by
DNA polymerases
explain how DNA is synthesised by DNA polymers
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
what does DNA polymerase require to start synthesis
primer segment
what is a primer
often an oligonucleotide of RNA and removed once replication is completed
intrinsic to all polymerases is what
a separate 3/ to 5/ exonuclease activity
what does the 3/ to 5/ exonuclease activity do
double checks that the last nucleotide added to the growing chain is correct before DNA polymerase can proceed to the next template base
what does helicases do
separates two parental strands by breaking hydrogen bonds using energy derived from ATP
what does topoisomerase do
relives stress on double helix structure created by separation of 2 strands
what do DNA binding proteins do
stabilize the separated strands
what do primases do
synthesize primer strand which polymerase binds to in initiation of DNA synthesis
what do polymerases do
synthesize DNA
what are and what do exonucleases do
integral parts of polymerase protein
double checks insertion of bases
why are DNA ligases used
at the end of replication, primer is removed, leaving a phosphodiester nick in DNA. ligases repair this break
how many stages of DNA replication are there
3
what are the 3 stages of DNA replication called
initiation, elongation and termination
what happens during the initiation stage
helicases open the DNA helix at a replicating origin - an area rich in A-T base pairings, called autonomously replicating sequences
what happens during elongation
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
what happens during the synthesis of the lagging strand
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
what happens during the termination stage
replication fork reaches a termination sequence and the process ends
