D1.1.8 DNA primase, DNA polymerase I, DNA polymerase III and DNA ligase in replication (HL) Notes

Functions of DNA Primase, DNA Polymerase I, DNA Polymerase III, and DNA Ligase in Replication

1. DNA replication is a highly coordinated process involving multiple enzymes, each with a specific role.

DNA Primase: Laying the Foundation

1. DNA polymerases can’t start synthesizing a new strand on their own.
2. They need a starting point, a short segment of RNA called a primer.

Key Functions of DNA Primase

1. Synthesizes RNA Primers: DNA primase creates a short RNA primer (about 10 nucleotides long) on the template strand.
2. Provides a 3′-OH Group: The RNA primer offers a free 3′-OH group, which is essential for DNA polymerase III to begin adding DNA nucleotides.
3. Multiple Primers on the Lagging Strand: On the lagging strand, DNA primase adds a new primer for each Okazaki fragment.

DNA Polymerase III: The Main Builder

1. DNA polymerase III is the workhorse of DNA replication, responsible for assembling the majority of the new DNA strand.
2. It is the primary enzyme responsible for synthesizing new DNA strands during replication in prokaryotes.

Key Functions of DNA Polymerase III

1. Synthesizes DNA in the 5′ to 3′ Direction: Adds nucleotides to the growing DNA strand, using the template strand as a guide.
2. High Processivity: Can add thousands of nucleotides without detaching, ensuring efficient replication.
3. Proofreading Ability: Checks each nucleotide after adding it, removing and replacing incorrect ones to minimize errors.

DNA Polymerase I: The Cleaner

1. Once DNA polymerase III has synthesized the new DNA, the RNA primers need to be removed and replaced with DNA.
2. This is where DNA polymerase I comes in.
3. An enzyme that removes RNA primers and replaces them with DNA nucleotides during replication.