DNA replication

Semi-conservative replication

The mechanism of DNA duplication where the double helix unzips and each parent strand serves as a template, yielding two DNA molecules each composed of one original strand and one newly synthesised strand.

Conservative replication model

A hypothesis stating that the original DNA molecule remains completely intact while a totally new double-stranded copy is synthesized.

Meselson-Stahl experiment

An investigation using heavy ($15\text{N}$) and light ($14\text{N}$) nitrogen isotopes in bacteria to prove that DNA replication is semi-conservative.

Role of density gradient centrifugation in the Meselson-Stahl experiment

To separate DNA molecules based on density, causing heavier DNA strands ($15\text{N}$) to sink lower, intermediate hybrid DNA ($15\text{N}/14\text{N}$) to rest in the middle, and lighter DNA ($14\text{N}$) to remain higher in the test tube.

Meselson-Stahl experiment: DNA band result after generation 1 in $14\text{N}$ medium

A single intermediate band composed entirely of hybrid DNA containing one heavy ($15\text{N}$) strand and one light ($14\text{N}$) strand.

Meselson-Stahl experiment: DNA band result after generation 2 in $14\text{N}$ medium

Two equal bands: one intermediate band ($15\text{N}/14\text{N}$ hybrid DNA) and one light band ($14\text{N}/14\text{N}$ DNA).