Translation at the Ribosome
The ribosome reads codons and tRNA brings the matching amino acid, turning a base sequence into an amino acid sequence. The code is degenerate, non-overlapping and read from a fixed start.
What a learner can do afterwards
- Matches a codon to its anticodon and says what the tRNA carries.
- Uses a codon table to build a short amino acid sequence from an mRNA sequence.
- Explains what degeneracy means for a change in the third base of a codon.
1 · Read
Ribosomes read mRNA in groups of three bases called codons. Reading starts at AUG, which also brings the first amino acid, methionine. With four bases taken three at a time there are 64 codons for about 20 amino acids. Most amino acids therefore have several codons, and the difference often sits in the third base. That sharing is called degeneracy.
The ribosome is built from a small and a large subunit clamped around the mRNA. Transfer RNAs dock one codon at a time, each anticodon pairing with its codon. Every tRNA carries its amino acid, and the ribosome links each new arrival to the growing chain. Then the message slides along by exactly one codon.
Try a short message: AUG followed by CUA, then a stop codon. AUG starts the chain with methionine, and CUA pairs with the anticodon GAU to add the next link. The stop codon fits no tRNA, so the finished chain is released to fold.
The reading frame is fixed from the start codon, and codons never overlap. Start one base off and every triplet after it changes, so always count in threes from AUG.
From AUG, triplet by triplet, tRNAs bring amino acids until a stop codon ends the chain.
2 · Watch
Take it off screen
Where it sits
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.