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DNA Replication Simulator

Semi-conservative replication — Class 11-12 / NEET

Class 11-12 · NEET
Replication Fork Animation
Replication Progress 0%
Base Pairing Rules
A — T
2 Hydrogen Bonds
Adenine · Thymine
G ≡ C
3 Hydrogen Bonds
Guanine · Cytosine
Interactive Sequence Builder
Template (3'→5'):
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New Strand (5'→3'):
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Current Phase
Initiation
Origin of replication recognized
Unwinding
Helicase breaks H-bonds
Priming
Primase adds RNA primer
Elongation
DNA Pol III synthesizes strands
Termination
Replication complete, ligase seals
Active Enzymes
Helicase — Unwinds double helix
Primase — Synthesizes RNA primer
DNA Pol III — Main replication enzyme
DNA Pol I — Removes RNA primer
Ligase — Joins Okazaki fragments
SSB Proteins — Stabilize single strands
Key Facts
🔵 Semi-conservative: each new DNA has 1 old + 1 new strand
🟢 5'→3' direction: DNA Pol III only adds nucleotides in 5' to 3'
🟡 Leading strand: synthesized continuously
🟠 Lagging strand: synthesized in Okazaki fragments (~1000-2000 bp in prokaryotes)
🔴 Speed: ~1000 nucleotides/sec in E. coli

Semi-Conservative Replication

Meselson-Stahl experiment (1958) proved that each daughter DNA retains one original (parent) strand and one newly synthesized strand.

Replication Fork

The Y-shaped structure where the two DNA strands separate. Contains helicase, SSB proteins, primase, and DNA polymerases working simultaneously.

Okazaki Fragments

Short (~100-200 bp in eukaryotes) DNA fragments synthesized on the lagging strand. Named after Reiji Okazaki. Later joined by DNA Ligase.

Origin of Replication

Specific DNA sequences where replication begins. Prokaryotes have 1 (oriC); eukaryotes have multiple origins to complete replication faster.

DNA Polymerase III

Main replication enzyme in prokaryotes. Has 5'→3' polymerase activity and 3'→5' proofreading (exonuclease) activity. Error rate: 1 in 10⁹ bases.