DNA proof: Griffith (transformation) → Avery (DNase only destroys) → Hershey-Chase (^32P pellet / ^35S supernatant) → Watson-Crick (right-handed antiparallel double helix; A=T 2H-bonds; G≡C 3H-bonds; Chargaff's rules).

Replication: Semiconservative (Meselson-Stahl: Gen1=all hybrid; Gen2=50% hybrid + 50% light); DNA Pol III synthesizes ALWAYS 5'→3'; leading=continuous; lagging=Okazaki fragments (joined by ligase); primase makes RNA primer; RNA Pol needs NO primer.

Genetic code: 64 codons = 61 sense + 3 stop (UAA/UAG/UGA); AUG=start+Met; code is degenerate, non-ambiguous, non-overlapping, universal; ribosome A-site (arrival) → P-site (peptide bond) → E-site (exit).

Lac operon: allolactose (NOT lactose) = true inducer; repressor binds OPERATOR (not promoter); lacZ (beta-galactosidase) → lacY (permease) → lacA (transacetylase); super-repressor → constitutively OFF; nucleosome = octamer (2×H2A, H2B, H3, H4) + H1 linker (H1 NOT in octamer).

Numbers: Human genome = 3.2 × 10^9 bp; ~20,000–25,000 genes; <2% coding; nucleosome = ~200 bp (147 bp core); 3 RNA Pol in eukaryotes (Pol I=rRNA; Pol II=mRNA; Pol III=tRNA); VNTRs + Southern blotting = DNA fingerprinting.