DNA Structure, Replication, and Mutations - Revision Sheet

1. 📌 Essentials

• DNA a double helix composed of two complementary nucleotide chains.
• Nucleotides consist of a base (A, T, C, G), sugar (deoxyribose), and.
• Complementary base pairing: A-T and C-G.
• DNA replication occurs during the S phase, involving unwinding and copying.
• DNA polymerase synthesizes new strands by adding complementary nucleotides.
• Replication is semi-conservative: each daughter DNA has one original and one new strand.
• Mutations include substitutions, insertions, and deletions, affecting genetic sequences.
• Mutations can result from errors during replication or environmental mutagens (UV, X-ray).
• DNA repair mechanisms correct most errors but are not perfect.
• Mutations contribute to genetic diversity and evolution; can be inherited if in germ cells.
• Replication speed in eukaryotes: approx. 100 nucleotides/sec.
• Human chromosome 1: ~250 million nucleotides; replication duration: ~8 hours.

---