DNA Replication: Key Players and Process

Overview

• DNA replication involves several molecular entities or 'players.'
• Key enzymes and proteins orchestrate the replication process, which proceeds through initiation, elongation, and termination phases.
• DNA is read in the 3' to 5' direction and synthesized in the 5' to 3' direction.
• Replication occurs at origins of replication, identified by DNA helicase, and proceeds with the help of various enzymes and proteins.

Key Enzymes & Proteins

1. Helicase

• Unwinds and unzips the DNA double helix.
• Creates leading and lagging strands.

2. DNA Primase

• Synthesizes RNA primer for DNA polymerase.

3. DNA Polymerase

• Adds nucleotides to the template strand.
• Moves in 3' to 5' direction along the template, synthesizing new DNA from 5' to 3'.

4. DNA Ligase

• Ligates Okazaki fragments on the lagging strand.

5. DNA Gyrase (Topoisomerase)

• Relieves torsional strain ahead of replication fork by introducing negative supercoils.

6. Single Strand Binding Proteins

• Prevents single-stranded DNA from forming secondary structures.

7. Clamp Proteins

• Stabilize DNA polymerase action by forming a sliding clamp around DNA.

DNA Replication Process

Initiation

• Begins at origins of replication, rich in adenine and thymine.
• Helicase unwinds DNA, creating replication forks consisting of leading and lagging strands.
• DNA primase adds RNA primer to initiate DNA synthesis.

Elongation

• DNA polymerase synthesizes new DNA strands by adding nucleotides.
• Leading Strand: Synthesized continuously in 5' to 3' direction.
• Lagging Strand: Synthesized discontinuously, forming Okazaki fragments.
  • DNA pol alpha extends RNA primer.
  • Okazaki fragments are formed and joined by DNA ligase.

Termination

• In bacteria, replication ends when replication forks meet.
• In eukaryotes, ends at telomere regions, causing telomere shortening over time.

Additional Details

• DNA polymerase's accuracy is enhanced by proofreading capabilities and mismatch repair mechanisms.
• Error rate: Less than one mistake per 10^9 nucleotides.
• Telomere shortening is a natural process related to aging and is covered in more detail separately.