Expansion
Transcription in the nucleus, processing, then translation on ribosomes
Expansion
Transcription (nucleus)
- RNA polymerase II makes messenger RNA; I makes ribosomal RNA; III makes transfer RNA
- Promoter regions (TATA box) bind transcription factors
- Processing: 5-prime cap, poly-A tail, splicing of introns
Translation (cytoplasm)
- Initiation: small ribosomal subunit binds the cap, scans to the AUG start codon (methionine)
- Elongation: transfer RNAs with anticodons deliver amino acids; peptide bonds form in the P and A sites
- Termination at a stop codon: UAA, UAG or UGA
Genetic code properties: triplet, degenerate (multiple codons per amino acid), unambiguous, non-overlapping and nearly universal.
Mutations follow from the code:
- Silent: no amino acid change, usually in the third base (the wobble position)
- Missense: one amino acid changed, as in sickle cell disease
- Nonsense: premature stop codon, giving a truncated protein
- Frameshift: insertion or deletion not a multiple of three, usually severe
Antibiotic targets on the bacterial ribosome: aminoglycosides and tetracyclines at the 30S subunit, macrolides, clindamycin and chloramphenicol at the 50S.