AP BIOLOGY

Detailed explanation-1: -At the start of the initiation phase of translation, the ribosome attaches to the mRNA strand and finds the beginning of the genetic message, called the start codon (Figure 4). This codon is almost always AUG, which corresponds to the amino acid methionine.

Detailed explanation-2: -Although methionine (Met) is the first amino acid incorporated into any new protein, it is not always the first amino acid in mature proteins-in many proteins, methionine is removed after translation.

Detailed explanation-3: -Therefore, the initiating amino acid is always methionine in a natively synthesized protein even though non-AUG codons are used as an initiation codon.

Detailed explanation-4: -In both prokaryotic and eukaryotic cells, translation always initiates with the amino acid methionine, usually encoded by AUG.

Detailed explanation-5: -The start codon is the first codon of a messenger RNA (mRNA) transcript translated by a ribosome. The start codon always codes for methionine in eukaryotes and Archaea and a N-formylmethionine (fMet) in bacteria, mitochondria and plastids.