IB Biology Sub-topic D1.1 Notes

Once DNA's structure was determined, the process of its replication needed to be determined. At the onset, this was tied between three main theories of replication existing at the time:

1. Conservative replication - the theory that both parent strands remain together (conserved), and an entirely new duplicate is formed.
2. Semi-conservative replication - the theory that the  parent strands break apart and each help form a new strand to produce two half-new and half-old copies.
3. Dispersive replication - the theory that the parent strands are cut and split up randomly to then produce copies with random amount of old and new DNA.

Meselson and Stahl determined that DNA replication was semi-conservative. You are expected to know this superficially, whilst HL students will learn this process in more detail. It occurs as follows:

1. Helicase unwinds and separates the double helix by breaking hydrogen bonds between DNA strands.
2. DNA polymerase links nucleotides to the pre-existing strands via complementary base pairing to form two new identical strands.
3. The strands separate and wind back into a double helix.

This method of replication via complementary base pairing has a high accuracy as only certain nucleotides are able to bind to another successfully. Deep knowledge of the process also allows for a number of industrial applications, such as DNA profiling.