3rd hour

DNA REPLICATION Replication begins at special sites called

origin of replication

A stretch of DNA having a specific sequence of nucleotides

Protein that initiate DNA replication recognize this sequence and attach to the DNA

Two strands of DNA separate and opening up a replication ‘bubble’

The Process Of DNA Replication

1)Unwound DNA strandEnzymes involved Function

DNA helicase enzymes

Separating the two strand of DNA

Helix-destabilizing proteins

bind to single DNA strand, preventing re-formation of the double helix until strands are

copied

Topoisomerase/girase

prevent the formation of knots during replication

2. DNA Synthesized

Leading Strand

DNA synthesize: start from 5’ end 3’end toward replication fork.

require an RNA primer first synthesised at the

point of initiation of replication.

Enzyme : primase

Then primase is displaced by DNA polymerase later will synthesize DNA.

Ribonuclease will digest the RNA primer.

DNA replication is

continuous.

Lagging strand

DNA synthesize: start from 5’ end

3’end Away from the

replication fork. DNA replication is

discontinuous.

require an RNA primer first synthesized at the point of initiation of

replication. synthesized by a protein complex known

as primase.

Then primase is displaced by DNA polymerase later will synthesize DNA.

Lagging Strand Only short piece

can be synthesize because DNA Polymerase would need to move far away from the fork.

These short segments called Okazaki fragments.

2)DNA Synthesize (continue)

3’ end 5’end

Leading strand Lagging strand

Start synthesizing from the 3’ strand end

Start synthesizing from the 5’ strand end

*The fragment joined together by DNA ligase.*Lastly, two double helix strand are formed.

Enzymes involved in DNA Replication DNA helicase : Unwind the double helix Primase : Synthesize RNA primer and

initiates the replication. DNA Polymerase : Synthesizes DNA. DNA Ligase : Joins the ends of DNA

segments.