Functions in replication explains how DNA is copied, checked, amplified or analysed through specific strand relationships, enzymes and molecular techniques.
Coverage 2013–2024 · Updated 16 Jul 2026
In prokaryotic DNA replication, primase, DNA polymerase III, DNA polymerase I and DNA ligase perform distinct sequential jobs.
| Enzyme | Required function |
|---|---|
| DNA primase | Synthesizes short RNA primers that provide a 3′ end |
| DNA polymerase III | Extends from each primer by adding DNA nucleotides 5′→3′; performs most new-strand synthesis |
| DNA polymerase I | Removes RNA primers and replaces them with DNA nucleotides |
| DNA ligase | Seals remaining nicks in the sugar–phosphate backbone, joining adjacent DNA sections |
On the lagging strand, primase repeatedly starts fragments, polymerase III extends them, polymerase I replaces each primer, and ligase seals the final backbone gaps.
This named-enzyme sequence is limited to the prokaryotic system. Polymerase I replaces primers; ligase does not synthesize the missing DNA nucleotides.
This objective is assessed through structured response, commonly using Identify / Explain / Outline.
Identify / Explain / Outline / Describe
Build the answer around this relationship: Functions in replication depends on matching each strand, enzyme or laboratory step to its exact function.
Saying helicase forms new strands instead of unwinding DNA and breaking hydrogen bonds.
Representative question
Describe the function of three named enzymes involved in DNA replication.
DNA strands have 5' and 3' ends; DNA polymerase adds nucleotides to the 3' end, so new DNA forms 5' to 3'. Leading strand synthesis is continuous; lagging strand synthesis is discontinuous as Okazaki fragments using repeated RNA primers. In the prokaryotic model, primase starts, DNA polymerase III extends, DNA polymerase I replaces primers, and ligase joins fragments. DNA polymerase III removes mismatched nucleotides from the 3' end; proofreading improves copying accuracy and reduces mutations.
