Question

When does the codon AUG signal the start of a protein? When does it code for the amino acid methionine?

Short answer

When codon AUG comes at the beginning of an mRNA, it signals the start of protein synthesis, and when it appears in the middle of a series of codons, it specifies or codes for the amino acid methionine.

Step-by-step solution

Introduction

The codon AUG codes for methionine and also functions as an initiation site: translation into protein begins at the first AUG in an mRNA's coding region. The additional start codons identified by GenBank are uncommon in eukaryotes and code for Met/fMet in most cases.

Explanation

Codon AUG marks the start of protein synthesis when it appears at the beginning of an mRNA, and it specifies or codes for the amino acid methionine when it appears in the middle of a series of codons.