DNA Replication
DNA replication is the biological process by which a cell makes an identical copy of its DNA before cell division. This ensures that genetic information is faithfully transmitted from parent cells to daughter cells.
Semi-Conservative Replication
DNA replication follows a semi-conservative mechanism, first demonstrated by Meselson and Stahl in 1958. This means:
- 1The double helix "unzips" by breaking hydrogen bonds between base pairs
- 2Each original strand serves as a template for a new complementary strand
- 3Each resulting DNA molecule contains one original (parental) strand and one newly synthesized strand
Key Insight: This mechanism ensures high fidelity in genetic
inheritance because each new DNA molecule retains half of the original genetic material.
3D Model: Semi-Conservative Conservation
Interactive visualization — available in the full lesson
Key Replication Enzymes
| Enzyme | Function |
|---|---|
| Helicase | Unwinds and separates the double helix by breaking hydrogen bonds |
| Primase | Synthesizes short RNA primers to initiate DNA synthesis |
| DNA Polymerase III | Main enzyme that adds nucleotides in the 5' → 3' direction |
| DNA Polymerase I | Removes RNA primers and replaces them with DNA |
| DNA Ligase | Joins Okazaki fragments by forming phosphodiester bonds |
| Topoisomerase | Relieves tension ahead of the replication fork by cutting and rejoining DNA |
| Single-Strand Binding Proteins (SSBs) | Stabilize separated strands and prevent re-annealing |
Interactive visualization — available in the full lesson