dna replication unit 4 – molecular genetics (ch. 5.2)
TRANSCRIPT
DNA Replication Unit 4 – Molecular Genetics (Ch. 5.2)
DNA Replication
DNA replication occurs in three phases:
• Initiation phase: a portion of the DNA double helix is unwound to expose the bases for new base pairing.
• Elongation phase: two new strands of DNA are assembled using the parent DNA as a template. The new DNA molecules (composed of one parent strand and daughter strand) re-form into double helices.
• Termination phase: the replication process is completed and the two new DNA molecules separate from each other.
Initiation
5’
3’ 5’
3’
origin of replication
Initiation
5’
3’
5’
3’
5’
3’
helicase
Initiation
5’
3’
5’
3’
helicase
SSBs single-strand-binding protein
SSBs SSBs
SSBs SSBs SSBs
replication fork replication bubble
Elongation
5’
3’
5’
3’
helicase
SSBs SSBs SSBs
SSBs SSBs SSBs
DNA polymerase
III
leading strand
Elongation
5’
3’
5’
3’
helicase
SSBs SSBs SSBs
SSBs SSBs SSBs
DNA polymerase
III
RNA primer
lagging strand
Okazaki fragment
primase
Elongation
5’
3’
5’
3’
helicase
SSBs SSBs SSBs
SSBs SSBs SSBs
DNA polymerase
III
DNA ligase DNA
polymerase I
Termination
5’
3’ 5’
3’
5’
3’ 5’
3’
Correcting Errors during DNA Replication
5’
3’ 5’
3’template strand
new strand
!!!!!
DNA polymerase
II
exonuclease
mismatch repair