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AP Biology · Unit 6: Gene Expression & Regulation

6.4 Translation

mRNA to protein

Translation builds a protein from mRNA at the ribosome. The mRNA is read in three-base units called codons, each specifying one amino acid. Translation begins at the start codon AUG (methionine) and ends at a stop codon.

The role of tRNA

Transfer RNA (tRNA) brings amino acids to the ribosome. Each tRNA has an anticodon that base-pairs with the matching mRNA codon, ensuring the right amino acid is added. The genetic code is nearly universal and redundant (multiple codons can code for the same amino acid).

Key terms

Translation
Building a protein from mRNA at the ribosome.
Codon
A group of three mRNA bases that codes for one amino acid.
tRNA & anticodon
tRNA carries an amino acid; its anticodon pairs with the mRNA codon.
Start codon (AUG)
Signals the start of translation and codes for methionine.
Genetic code (redundant)
Nearly universal, and multiple codons can specify the same amino acid.

Try an AP-style question

Data

An mRNA reads 5'-AUG UUU GGC UAA-3'. Codons: AUG = Met, UUU = Phe, GGC = Gly, UAA = stop.

What polypeptide is produced?

  1. Met–Phe–Gly–Stop
  2. Met–Phe–Gly
  3. Gly–Phe–Met
  4. Phe–Gly
Show the answer

B. Translation starts at AUG and ends at the stop codon, which codes for no amino acid.

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