Molecular Biology for the MCAT

DNA Replication

Semiconservative replication:

• Helicase unwinds DNA
• Primase lays RNA primer
• DNA Pol III extends 5'→3'
• Ligase seals Okazaki fragments on lagging strand

Transcription

RNA polymerase reads template 3'→5', synthesizes mRNA 5'→3'.

Post-transcriptional processing:

• 5' cap (7-methylguanosine)
• 3' poly-A tail
• Intron splicing (alternative splicing → multiple proteins from one gene)

Translation

• Start codon: AUG (methionine)
• Stop codons: UAA, UAG, UGA
• tRNA anticodon pairs with mRNA codon

Biotechnology

• PCR: Amplifies DNA using primers + Taq polymerase + thermal cycling
• Gel electrophoresis: Separates by size (smaller = faster)
• CRISPR-Cas9: Gene editing with guide RNA
• Blots: Southern (DNA), Northern (RNA), Western (protein) — SNOWdrop