Prokaryotic DNA replication

Proteins needs for DNA replication

1. DnaA

2. DNA helicase

3. Single stranded binding proteins

4. DNA gyrase

5. Primase

6. DNA polymerase

7. DNA polymerase III

8. DNA polymerase 1

9. DNA ligase

where is the origin of replication located in prokaryotes

a region called the oriC that is AT rich

DnA protein

initiator protein

Initiation of DNA replication

1. DnA protein binds to DnA binding sites on oriC causing it to unwind. 

2. Helicase unwinds DNA at replication fork in 5’→3’ to separate hydrogen bonds allowing access to template strand

3. Single stranded binding proteins bind to keep DNA unwound and avoid hairpins

4. DNA gyrase makes breaKs in DNA ahead of replication machinery to relieve torsion from helicase.

primase

an enzyme that synthesizes a short primer (10-12 N) with provides 3’OH group for DNA polymerase to begin synthesis

Elongation in prokaryote DNA replication

1. Primase binds to helicase at replication fork to start making the primer

2. primer is used only to 5’ end of leading strand, and a new primer is generated at beginning of each okazaki fragment of the leading strand.

3. DNA polymerase elongates the DNA strand bu adding nucleotides to the 3’ end of the growing strand, following templates sequence.

In E. coli. there are 5 different DNA polymerases

DNA polymerase I

has 5’ →3’ polymerase activity, and both directions of exonuclease activity (one of a kind!). Its specialty is replacing RNA nucleotides with DNA nucleotides.

DNA polymerase III

• is the main DNA polymerase, 5’→ 3’ polymerase activity, and 3’ →5’ exonuclease activity.

Exonuclease activity

• proofreading ability, and replaces incorrectly added nucleotides with correct ones.  

How does the process of lagging strand DNA synthesis make an intact DNA strand?

1. Primase synthesizes primers

2. DNA pol III extends primers and synthesizes okazaki frgaments in 5’→3’

1. once DNA pol III reachs 5’ end of previous primer, its replaced by DNA pol I. which removes primer and fills in gap with DNA

2. DNA ligase seals the gap between okazaki fragments creating a continuous DNA strand.

Summery of proteins in prokaryotic DNA replication