IB Biology Topic D1.1.2: Semi-conservative Nature of DNA Replication Notes

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DNA Replication Is Semi-Conservative

1. When DNA replicates, the two strands of the double helix separate.
2. Each original strand acts as a template for a new complementary strand.
3. The result is two identical DNA molecules, each with one old strand and one new strand.
4. This preserves genetic information with high fidelity during cell division.

Complementary Base Pairing Keeps Copies Accurate

1. Template-driven synthesis
   1. DNA polymerase reads the template strand.
   2. For each base on the template, it adds the complementary nucleotide to the new strand.
2. Hydrogen bonding as a quality check
   1. Correct base pairs (A-T or C-G) form stable hydrogen bonds.
   2. Incorrect pairs, such as A-C, do not form proper hydrogen bonds.
   3. If bonding is weak or absent, the wrong nucleotide is rejected.

Base Pairing Gives High Fidelity

1. Complementary base pairing means the template sets the base sequence of the new strand.
2. This makes replication remarkably accurate, copying the genome with very few errors.