DNA Replication Notes

UNITY DNA

• DNA is antiparallel.
• Backbone consists of:
  • 5-carbon sugar (deoxyribose).
  • Phosphate.
  • Nitrogenous base.
• A + T form 2 hydrogen bonds, while G + C form 3 hydrogen bonds.
• Bases include Adenine (A), Thymine (T), Guanine (G), and Cytosine (C).
• A single strand of DNA has 1 backbone.
• Purines (A, G) pair with pyrimidines (T, C).
• More hydrogen bonds lead to greater stability.
• Carbons are labeled 1' to 5' on the deoxyribose sugar.
• DNA levels are antiparallel.

Nucleotides

• Nucleotides are the building blocks of DNA.

Replication

• If you have one strand, you can synthesize the other.
• Daughter strands are newly made; parental strands are original strands.

Replication Models

• Semiconservative: Each new DNA molecule contains one original and one new strand.
• Conservative: Original strands stay together, and a new double helix is created.
• Dispersive: Strands have chunks of both old and new DNA.

Replication Process

• Replication opens up a replication bubble.
• DNA helicase pulls apart the strands.
• Topoisomerase removes knots caused by overwinding.
• SSBP (single-stranded binding proteins) stabilize separated strands.
• Replication origin is the starting point of replication.
• Primase inserts an RNA primer at the origin, allowing DNA polymerase to begin synthesizing daughter strands.
  • Primase builds RNA primers (e.g., 5'-UACGUU-3').
  • Given a DNA sequence (e.g., 5'-ATGCAA-3'), DNA is always built in the 5' to 3' direction.
• DNA polymerases catalyze new DNA replication.

DNA Polymerases

• DNA polymerases:
  • Require a primer.
  • Need a template (parental strand) to make DNA.
  • Only build in the 5' to 3' direction.

Leading Strand

• Leading strand is synthesized continuously towards the replication fork.