Question

Which of the following amino acid is the first one to include in almost all the protein synthesis process?

• A. Glycine
• B. Methionine
• C. Thymine
• D. Proline

Hint:

Translation initiation always begins at the start codon AUG, which codes for the amino acid methionine (or formyl-methionine in prokaryotes).

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Translation is the process by which ribosomes synthesize proteins using the genetic code on an mRNA template.
This process begins at a specific start codon on the mRNA, which determines the first amino acid incorporated into the growing polypeptide chain.

Step 2: Detailed Explanation:
In almost all living organisms, the initiation of translation is directed by the start codon AUG on the mRNA.
The anticodon of the initiator transfer RNA (tRNA) binds specifically to this start codon.
In eukaryotes, the initiator tRNA carries the amino acid methionine.
In prokaryotes, the initiator tRNA carries a modified version, \(N\)-formylmethionine (fMet).
Because protein synthesis almost always starts at an AUG codon, methionine is the first amino acid incorporated into virtually all newly synthesized polypeptide chains.
In many mature proteins, this initial methionine is subsequently removed by post-translational modification enzymes (like methionine aminopeptidases), but it remains the universal starting amino acid during the translation process.
The other options (glycine, proline) are standard amino acids added during elongation, and thymine is a nitrogenous base found in DNA, not an amino acid.

Step 3: Final Answer:
Hence, the correct option is (B).