Start codon

Definition

A start codon is a specific sequence of nucleotides in mRNA that signals the beginning of protein synthesis. The most common start codon is AUG, which codes for the amino acid methionine.

5 Must Know Facts For Your Next Test

1. The start codon initiates the translation process by signaling the ribosome where to begin mRNA translation.
2. In almost all organisms, the start codon AUG also codes for methionine, which is usually the first amino acid in a newly synthesized protein.
3. Mutations in the start codon can prevent proper protein synthesis and lead to nonfunctional proteins or diseases.
4. The initiation complex, including tRNA and other proteins, assembles at the start codon to begin translation.
5. While AUG is the most common start codon, alternative start codons like GUG and UUG can occasionally function as start sites in some organisms.

Review Questions

• What sequence of nucleotides typically serves as the start codon in mRNA?
• How does a mutation in the start codon affect protein synthesis?
• What amino acid does the common start codon code for?

Related terms

mRNA:

Messenger RNA that carries genetic information from DNA to the ribosome for protein synthesis.

Ribosome:

A molecular machine that facilitates the linking of amino acids during protein synthesis.

tRNA:

Transfer RNA that brings amino acids to the ribosome corresponding to each codon's instructions during translation.