DNA Structure & Replication - Quick Reference

Central Dogma

  • The central dogma of information flow: DNA→RNA→Protein\text{DNA} \rightarrow \text{RNA} \rightarrow \text{Protein}
  • Information stored in DNA; copied to RNA (transcription); used to make proteins (translation).

DNA Structure and Base Pairing

  • DNA is usually double-stranded; two strands held together by hydrogen bonds between bases on opposite strands.
  • Base-pairing rules: A pairs with T,G pairs with C.A \text{ pairs with } T,\quad G \text{ pairs with } C.
  • Complementary base pairing enables copying of genetic material.

History: Watson–Crick Model (brief context)

  • Watson & Crick combined Chargaff’s rules and Franklin’s data to propose a structure that suggests a copying mechanism via base pairing.

DNA Replication Basics

  • DNA replication uses both strands as templates.
  • Copying steps:
    1) Separate the two strands
    2) Use each strand as a template
    3) Add nucleotides using base-pairing rules to form two copies
  • DNA synthesis direction: 5′→3′5' \rightarrow 3'; new nucleotides are added at the 3′3' end.

Origins and Replication Fork

  • Replication begins at origins; the E. coli chromosome has 11 origin, each eukaryotic chromosome has many.

Replication Fork: Leading vs Lagging

  • Replication fork forms; Synthesis on the LEADING strand is continuous; on the LAGGING strand is discontinuous (Okazaki fragments).

RNA Primers and Joining

  • RNA primers are removed by DNA polymerase I, which uses 5' to 3' exonuclease activity.
  • Okazaki fragments are joined by DNA ligase, sealing the nicks.