The red bead is helicase, unwinding the parent double helix at the replication fork and splitting it into two template strands. Because both new strands can only be built 5'→3', and the two templates run in opposite directions, the two daughter strands are made differently: on the leading side (green) DNA polymerase follows the fork continuously; on the lagging side it can only work backwards in short bursts called Okazaki fragments (amber → sealed), and DNA ligase (violet bead) stitches each fragment to the next once it's finished.
leading: dNew/dt = v_fork (continuous)
lagging: fragment[k] grows until length L, then ligase joins it to fragment[k-1]
- Fork speed — how fast helicase unwinds the helix; the lagging-strand gap you see behind the fork is real: fragment synthesis is inherently slower than continuous leading-strand synthesis.
- Proofreading fidelity — the chance DNA polymerase's exonuclease activity catches a mispaired base (briefly flashes red) before it becomes permanent; low fidelity leaves visible red mutations behind.
- Blue rungs = A–T base pairs, gold rungs = G–C base pairs — every rung you see is a real base pair carried through to both daughter duplexes, unchanged, exactly as semiconservative replication predicts.
Real-world relevance: this asymmetry — one strand smooth, one stitched from fragments — is why replication needs a whole toolkit (helicase, primase, two polymerases, ligase) instead of one enzyme, and why proofreading fidelity is the single biggest lever on mutation rate.