DNA Replication: Mechanisms Overview

What occurs during the termination phase of DNA replication?

What is the main role of telomerase in eukaryotic DNA replication?

Which strand is synthesized continuously during DNA replication?

How does DNA polymerase contribute to the integrity of the DNA sequence?

What is a characteristic of the lagging strand during DNA replication?

What initiates the unwinding of double-stranded DNA during replication?

How does DNA polymerase add nucleotides to the leading strand?

What distinguishes the synthesis of the leading strand from that of the lagging strand?

What is the role of DNA ligase in DNA replication?

Why does primase lay down multiple primers on the lagging strand?

What stabilizes unwound single-stranded DNA during replication?

In what direction does DNA polymerase synthesize new DNA?

What happens to the RNA primers after they are no longer needed on the lagging strand?

DNA Replication: Initiation, Elongation, and Termination

Initiation: The beginning of DNA replication.
- Replication begins at origins of replication, multiple sites to speed replication in eukaryotes.
- Helicase unwinds the DNA double helix, creating the replication fork, by breaking hydrogen bonds between base pairs.
- Single-strand binding proteins (SSBs) stabilize the unwound single strands to prevent them from reannealing.
- Primase synthesizes short RNA primers to provide starting points for DNA polymerase to extend new DNA.
- One primer is needed on the leading strand, and multiple primers are needed on the lagging strand.

Elongation

Leading Strand: Continuous synthesis in the 5' to 3' direction, matching the movement of the replication fork. DNA polymerase continuously adds nucleotides in one direction.
Lagging Strand: Discontinuous synthesis in short fragments called Okazaki fragments. Synthesized away from the replication fork. DNA polymerase adds nucleotides in the 5' to 3' direction from each primer.
DNA Ligase joins the Okazaki fragments together into a continuous strand.
DNA pol moves in the 5' ----> 3' direction.

Termination

Replication ends when replication forks meet or when the entire DNA molecule is copied.
Telomeres (found only in eukaryotic linear DNA): Specialised structures at the ends of chromosomes that require specialized enzymes (telomerase) for complete replication.
Proofreading and repair enzymes check for and correct errors for higher accuracy.

Leading vs Lagging Strands Summary

Feature	Leading Strand	Lagging Strand
Synthesis	Continuous	Discontinuous (Okazaki fragments)
Primer Needs	One	Multiple
Direction	5' to 3', same as replication fork	5' to 3', opposite to replication fork
Enzyme Completion	Continuous strand	Joined fragments by DNA ligase

This quiz covers the key processes of DNA replication including initiation, elongation, and termination. Understand the roles of helicase, DNA polymerase, and the differences between leading and lagging strands. Test your knowledge on how these mechanisms work together to ensure accurate DNA duplication.