- Amazing process : 6 billion base pairs in human genome.
- Equivalent to 1000 books each with 1000 pages of 12 font text.
- Error rate < 1 error per billion base pairs.
- About 50 base pairs (eukaryotic cells) per second are replicated.
- A single DNA helix is split into two strands.
- A new DNA strand is made to complete each strand of old DNA.
- This is called semi-conservative replication. New DNA helix is ½ of the old DNA helix.
- Replication begins at replication origin. Eukaryote DNA have many origins.
- Origin forms a bubble as helicase opens the helix.
- Each end of the bubble called a replication fork.
- DNA polymerases travels along strand and makes complementary strand.
- DNA polymerase moves along DNA template in 3' to 5' direction.
- The new DNA builds from 5' to 3' (the complement remember).
- Leading strand made directly.
- Lagging strand assembled in segments (Okazaki fragments) by ligase.
- Single-strand binding proteins keep the single DNA strand stable.
- Initial errors are 1 in 10,000 base pairs.
- DNA polymerases do proof reading.
- Complementary nature of DNA allows such high accuracy.
- Many repair enzymes correct, usually by excising and using complementary strand.
- UV can cause two adjacent thymine bases to bond covalently.
- The two complementary adenine are unbonded and the helix has a kink.