Molecular Basis of Inheritance

About this unit

This unit explains the chemistry of heredity. It covers the experiments that proved DNA is the genetic material, the structure and packaging of DNA, how DNA copies itself, and how information flows from DNA to RNA to protein (the central dogma). It also explains the genetic code, how gene expression is regulated using the lac operon, the Human Genome Project and DNA fingerprinting. This unit is the foundation for biotechnology.

Key ideas

• DNA is a double-stranded, antiparallel helix with complementary base pairing (A–T, G–C).
• Griffith, Avery–MacLeod–McCarty and Hershey–Chase showed DNA is the genetic material.
• Replication is semi-conservative, as shown by Meselson and Stahl.
• Transcription makes RNA from a DNA template; translation makes protein on ribosomes.
• The genetic code is a triplet, degenerate, nearly universal and non-overlapping.
• The lac operon shows how bacteria switch genes on and off.

How to prepare

Learn the key experiments in order with their conclusions. Draw the replication fork, a transcription unit and the lac operon. Practise questions on base composition (Chargaff's rule), codon counting and polypeptide length.