DNA Replication

Study Notes

Each parent strand of DNA is incorporated into a new double-stranded DNA molecule.
This model was proven by experiments conducted by Meselson and Stahl.

DNA must "unzip" using an enzyme called DNA helicase, which breaks the H-bonds between base pairs starting at the replication origin.
The point of separation of the two strands of DNA is called the replication fork.
Tension in the unwinding strand is relieved by topoisomerases, which cleave one or two of the DNA strands, allowing them to untwist, then rejoin the strands.
The strands are kept apart by single-stranded binding proteins (SSBs).

The leading strand is built in a continuous fashion by DNA polymerase III by adding nucleoside triphosphates onto the 3' end of the parent strand.
New DNA is assembled 5' to 3'.
Replication starts when RNA primase puts down a 'starting point' - RNA primer (about 10 to 60 RNA ribonucleotides long).
Only one primer is needed for the leading strand, and it is built continuously toward the replication fork.
The lagging strand is built away from the replication fork in short fragments called Okazaki fragments by DNA Polymerase III.
RNA primers are continuously added to the 5' end of the new strand (or the 3' end of the parent strand).
DNA polymerase I removes the RNA primers and replaces them with DNA nucleotides (while also proofreading the strands).
Okazaki fragments are connected by DNA ligase by creating phosphodiester bonds between nucleotides.

DNA polymerase I and III proofread new strands.
DNA polymerase II repairs damage to DNA, including damage that occurs between replication events.

Prokaryotic genomes are much smaller and usually contain just one replication bubble.
Eukaryotic DNA is very long and linear, therefore thousands of replication bubbles can appear.

Each parent strand of DNA is incorporated into a new double-stranded DNA molecule.
This model was proven by experiments conducted by Meselson and Stahl.

DNA must "unzip" using an enzyme called DNA helicase, which breaks the H-bonds between base pairs starting at the replication origin.
The point of separation of the two strands of DNA is called the replication fork.
Tension in the unwinding strand is relieved by topoisomerases, which cleave one or two of the DNA strands, allowing them to untwist, then rejoin the strands.
The strands are kept apart by single-stranded binding proteins (SSBs).

The leading strand is built in a continuous fashion by DNA polymerase III by adding nucleoside triphosphates onto the 3' end of the parent strand.
New DNA is assembled 5' to 3'.
Replication starts when RNA primase puts down a 'starting point' - RNA primer (about 10 to 60 RNA ribonucleotides long).
Only one primer is needed for the leading strand, and it is built continuously toward the replication fork.
The lagging strand is built away from the replication fork in short fragments called Okazaki fragments by DNA Polymerase III.
RNA primers are continuously added to the 5' end of the new strand (or the 3' end of the parent strand).
DNA polymerase I removes the RNA primers and replaces them with DNA nucleotides (while also proofreading the strands).
Okazaki fragments are connected by DNA ligase by creating phosphodiester bonds between nucleotides.

DNA polymerase I and III proofread new strands.
DNA polymerase II repairs damage to DNA, including damage that occurs between replication events.

Prokaryotic genomes are much smaller and usually contain just one replication bubble.
Eukaryotic DNA is very long and linear, therefore thousands of replication bubbles can appear.