DNA Replication :

*It is a semi-conservative process

*The daughter DNA molecules produced consist of one progeny and one parental strand

DNA as Template

*Each strand of the parent DNA acts as template, make the new daughter strand

*Makes 2 new complete double helices

*Each with 1 old and 1 new strand

*DNA synthesis proceeds only in the 5' 3'direction which means that the strand being copied is been read in the 3' 5' direction

*DNA replication begins at specific base sequence (Origin of replication) when helicase binds to parental

*DNA and begins to unwind it (break the H bond)

*Each parent strand becomes a template used to synthesize the complimentary strand

*Single-strand binding (SSB) protein bind to single DNA strands and stabilize them

*Prevents the double helix from re-forming until the strand are replicated

*Both strand require RNA primer for initiation of synthesis because DNA can be elongated only by addition to 3' end of existing polynucleotide strand

Leading Strand (template 3’ – 5’)

*RNA primase synthesize the primer:

- 5-14 nucleotides

- To provide the 3’ OH end

*DNA polymerase binds to the 3’ end

- Add nucleotides to the growing end

*The primer will be digested by DNA polymerase

- Replaced by DNA

*Primer will be joined by DNA ligase

*DNA polymerase binds to the 3’ end

- Add nucleotides to the growing end

Lagging Strand (template 5’ – 3’)

*RNA primase synthesize the primer

*DNA polymerase binds to the 3’ end

- Add nucleotides to the growing end

*Moves discontinuously away from the replication fork

*Forms short fragments - Okazaki fragments

*The primer will bedigested by DNA polymerase

- Replaced by DNA

*All Okazaki fragments are joined by DNA ligase

*New complementary DNA strand 3’ - 5’

Animation : DNA Replication Process