Chapter 1: Proof That DNA is the Genetic Material (Historical Experiments)
Three landmark experiments established DNA as the hereditary molecule. Griffith's 1928 transformation experiment proved a heritable "transforming principle" existed, though he did not identify it. Avery, MacLeod, and McCarty (1944) used selective enzymatic destruction to show only DNase abolished transforming activity — identifying the principle as DNA. Hershey and Chase (1952) used radioactive isotopes (^32P for DNA; ^35S for protein) in bacteriophage T2 to physically demonstrate that DNA — found in the bacterial pellet — was the injected genetic material, while protein — found in the supernatant — remained outside.
Chapter 2: DNA Structure and Packaging
Watson and Crick's 1953 double helix model established DNA as a right-handed antiparallel double helix. Complementary base pairing (A=T, 2 H-bonds; G≡C, 3 H-bonds) follows Chargaff's rules. In eukaryotes, DNA is packaged into nucleosomes (200 bp DNA + histone octamer of H2A, H2B, H3, H4; H1 is the linker histone, not part of the octamer). Nucleosomes compact into the 30 nm fibre, loops, and ultimately the metaphase chromosome.
Chapter 3: DNA Replication
Replication is semiconservative (Meselson-Stahl, 1958). It proceeds bidirectionally from origins of replication. Key enzymes: helicase (unwinds), SSBs (stabilize), topoisomerase (relieves supercoils), primase (makes RNA primer), DNA Pol III (synthesizes 5'→3'), DNA Pol I (removes primers), ligase (joins fragments). The leading strand is continuous; the lagging strand forms Okazaki fragments joined later by ligase.
Chapter 4: Transcription and Post-Transcriptional Processing
RNA polymerase (no primer needed) reads the template strand 3'→5' and synthesizes mRNA 5'→3'. Eukaryotic pre-mRNA undergoes 5' capping, 3' polyadenylation, and intron splicing before export from the nucleus. Prokaryotic transcription and translation are coupled (no nuclear envelope). Three eukaryotic RNA polymerases: Pol I (rRNA), Pol II (mRNA), Pol III (tRNA, 5S rRNA).
Chapter 5: The Genetic Code
The code has 64 codons: 61 sense (encoding 20 amino acids) + 3 stop (UAA, UAG, UGA). AUG is the universal start codon (methionine). Code properties: degenerate, non-ambiguous, non-overlapping, comma-less, universal (nearly). Wobble at the third codon position allows one tRNA to recognize multiple codons.
Chapter 6: Translation
Translation initiates when the small ribosomal subunit binds the 5' cap of mRNA and scans to the first AUG. The large subunit joins to form the initiation complex. During elongation: aminoacyl-tRNA enters A-site; peptide bond forms (catalyzed by 23S rRNA); translocation shifts the ribosome one codon. Translation terminates when a stop codon enters the A-site and release factors trigger polypeptide release.
Chapter 7: Gene Regulation — Lac Operon
The Lac operon is a classic negative inducible system. The lacI-encoded repressor binds the operator and blocks transcription. Allolactose (formed from lactose by beta-galactosidase) is the true inducer — it binds the repressor, causing conformational change, releasing the operator, allowing transcription of lacZ (beta-galactosidase), lacY (permease), lacA (transacetylase) as a polycistronic mRNA.
Chapter 8: Human Genome Project and DNA Fingerprinting
The HGP (1990–2003) sequenced the entire 3.2 billion bp human genome and identified ~20,000–25,000 protein-coding genes, with only ~2% of the genome coding for proteins. DNA fingerprinting uses the high variability of VNTRs (Variable Number Tandem Repeats). Restriction-digested DNA is separated by gel electrophoresis, transferred to a membrane by Southern blotting, and hybridized with labelled probes that detect the unique VNTR pattern of each individual.