bilogy 101 july 9

Central Idea – Translation (Protein Synthesis)

• Translation = decoding of mRNA nucleotide sequence into an amino-acid sequence (polypeptide/protein).
• Directionality:
  • mRNA is threaded left → right through the ribosome.
  • The amino-acid chain is “read out” right → left.

tRNA, Codons & the Wobble Phenomenon

• Cells contain ≈ 40 distinct tRNA species, fewer than the 61 sense codons.
  • Reason: Wobble – the 3rd (3′) base of a codon can often pair non-canonically, letting one tRNA decode multiple codons.
  • Example ranges:
  • Tryptophan → only one codon.
  • Some amino acids → two codons.

- Others (e.g., Leu, Ser, Arg) → six codons.