Label the parts of the DNA replication fork.
The correct answer and explanation is :
Labeled Parts of the DNA Replication Fork
- Helicase – Unwinds the double-stranded DNA, creating the replication fork.
- Single-Strand Binding Proteins (SSBs) – Bind to the separated DNA strands to prevent them from reannealing.
- Primase – Synthesizes a short RNA primer needed for DNA polymerase to start replication.
- DNA Polymerase III – Adds nucleotides to the growing DNA strand in the 5’ to 3’ direction.
- Leading Strand – The continuously synthesized DNA strand in the direction of the replication fork.
- Lagging Strand – The discontinuously synthesized DNA strand, made in short Okazaki fragments.
- Okazaki Fragments – Short DNA fragments formed on the lagging strand.
- DNA Ligase – Joins Okazaki fragments to create a continuous DNA strand.
- Topoisomerase (Gyrase) – Relieves supercoiling ahead of the replication fork.
Explanation (300 words)
DNA replication is a highly coordinated process that ensures the accurate copying of genetic material before cell division. It occurs at the replication fork, a Y-shaped structure where DNA is unwound and new strands are synthesized.
Helicase plays a crucial role by breaking hydrogen bonds between the two DNA strands, creating two single-stranded templates. However, this unwinding creates tension ahead of the fork, which is relieved by topoisomerase. The exposed single strands are stabilized by SSBs, preventing them from reannealing.
For replication to begin, primase synthesizes a short RNA primer on each template strand, providing a starting point for DNA polymerase III, which adds nucleotides in the 5′ to 3′ direction. The leading strand is synthesized continuously in the same direction as the replication fork, while the lagging strand is synthesized in the opposite direction in short Okazaki fragments.
Each Okazaki fragment requires a primer, and once they are synthesized, DNA polymerase I removes the RNA primers and replaces them with DNA. Finally, DNA ligase seals the gaps between fragments, forming a continuous strand.
This intricate coordination ensures high-fidelity DNA replication, essential for genetic inheritance and cellular function.
