DNA Replication Revision Sheet

1. 📌 Essentials

• DNA replication copies the entire DNA molecule to produce two identical strands.
• Occurs in the nucleus of eukaryotic cells; cytoplasm of prokaryotes.
• Key enzymes: helicase, primase, DNA polymerase, ligase.
• Replication is semi-conservative: each new DNA contains one original.
• Directionality of synthesis: 5' to 3'.
• Leading strand: continuous synthesis; lagging strand:azaki fragments.
• Base pairing rules: A=T, C≡G.
• Replication begins at specific origins.
• Forks are Y-shaped structures where DNA unwinding occurs.
• Proofreading by DNA polymerase ensures fidelity.

2. 🧩 Key Structures & Components

• DNA molecule — double helix with antiparallel strands.
• Nucleotides — sugar (deoxyribose), phosphate, nitrogenous base.
• Base pairs — A=T (2 H-bonds), C≡G (3 H-bonds).
• Replication fork — site of active DNA unwinding.
• Origin of replication — specific sequence initiating replication.
• Enzymes:
  • Helicase — unwinds DNA
  • Primase — synthesizes RNA primer
  • DNA polymerase — adds nucleotides
  • Ligase — joins Okazaki fragments
• Okazaki fragments — short DNA segments on lagging strand.
• Single-strand binding proteins — stabilize unwound DNA.

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