Amino Acid Coded by the Start Codon

In the process of protein synthesis, also known as translation, messenger RNA (mRNA) carries the genetic information from DNA in the form of codons. A codon is a sequence of three nucleotide bases that specifies a particular amino acid or a stop signal.

Protein synthesis begins at a specific site on the mRNA molecule, which is indicated by a start codon. There is one primary start codon that signals the ribosome to begin translation.

The genetic code is nearly universal across different organisms. The start codon is universally recognized as AUG.

The codon AUG specifically codes for the amino acid methionine. This is true for both prokaryotic and eukaryotic organisms, although in prokaryotes, the initial methionine is often modified to N-formylmethionine (fMet), but the codon still specifies methionine.

Therefore, the amino acid coded by the start codon (AUG) for protein synthesis is methionine.

Let's look at the options provided:

• methionine: This is the amino acid coded by the start codon AUG.
• tryptophan: This amino acid is coded by the codon UGG.
• arginine: This amino acid is coded by several codons, including CGU, CGC, CGA, CGG, AGA, and AGG.
• More than one of the above: Only methionine is coded by the start codon.
• None of the above: Methionine is indeed coded by the start codon.

Based on the genetic code and the role of the start codon in protein synthesis, the correct amino acid is methionine.