Translation, the Genetic Code, and Protein Synthesis
Decoding mRNA
The Genetic Code
The genetic code is read in triplets called codons. Each codon specifies an amino acid or a stop signal. The code is nearly universal, degenerate, and nonoverlapping.
Translation Machinery
Ribosomes read mRNA from . tRNAs match codons through anticodons and deliver amino acids that are joined by peptide bonds.
Translation Stages
| Stage | Main Event |
|---|---|
| Initiation | Ribosome assembles at start codon |
| Elongation | Amino acids are added one by one |
| Termination | Stop codon triggers release |
Start and Stop
AUG usually serves as the start codon and codes for methionine. UAA, UAG, and UGA are stop codons.
What is a codon?
Codons are triplets of nucleotides read during translation.
Correct answer: A three-nucleotide sequence in mRNA
Why is the genetic code described as degenerate?
Multiple codons can encode the same amino acid.
Correct answer: Because most amino acids are specified by more than one codon.
Which molecule carries amino acids to the ribosome?
tRNA acts as an adaptor between codons and amino acids.
Correct answer: tRNA
Protein Folding and Function
A protein’s amino acid sequence influences its folding, localization, and activity. Mutations that alter the sequence can change structure and function.
What happens when a stop codon enters the ribosome A site?
Release factors recognize the stop codon and end synthesis.
Correct answer: Translation terminates and the completed polypeptide is released.