Biology: Molecular Biology & Genetics

Free MCAT study guide — Biological and Biochemical Foundations of Living Systems

DNA Structure & Replication

Enzyme	Function
Helicase	Unwinds double helix
Primase	Synthesizes RNA primers
DNA Pol III	Main replicative enzyme (5'→3'), proofreading (3'→5')
DNA Pol I	Removes primers, fills gaps
Ligase	Seals nicks between Okazaki fragments
Topoisomerase	Relieves supercoiling ahead of fork

Key Point: DNA replication is semiconservative. Leading strand = continuous. Lagging strand = Okazaki fragments.

Transcription & Translation

Key Point: mRNA processing (eukaryotes): 5' cap + 3' poly-A tail + splicing (introns out, exons joined).

Start codon: AUG (Met)   |   Stop codons: UAA, UAG, UGA

Genetics

p + q = 1   |   p² + 2pq + q² = 1

Key Point: HW conditions (no evolution): no mutation, no migration, no selection, large population, random mating.