Question:
Which of the following amino acids initiates protein synthesis in all organisms?
Which of the following amino acids initiates protein synthesis in all organisms?
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- Universal Start Codon: AUG
- Corresponding Amino Acid: Methionine (Met)
- In prokaryotes, it is N-formylmethionine (fMet).
This is the first amino acid located at the N-terminal end of newly synthesized proteins.
- Corresponding Amino Acid: Methionine (Met)
- In prokaryotes, it is N-formylmethionine (fMet).
This is the first amino acid located at the N-terminal end of newly synthesized proteins.
Updated On: Aug 13, 2026
- Glycine
- Methionine
- Thymine
- Proline
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The Correct Option is B
Solution and Explanation
Step 1: Understanding the Concept:
Translation is the process by which ribosomes synthesize proteins using an mRNA template.
The initiation of translation is a highly conserved molecular event guided by specific start codons and initiator tRNAs.
Step 2: Detailed Explanation:
In both prokaryotes and eukaryotes, the universal start codon on the mRNA transcript is AUG.
- This codon is recognized by a specialized initiator transfer RNA (tRNA).
- In eukaryotes, the AUG start codon recruits an initiator tRNA carrying the amino acid Methionine.
- In prokaryotes, plastids, and mitochondria, the initiator tRNA carries a modified form of this amino acid, known as N-formylmethionine (fMet).
During polypeptide chain elongation, the first amino acid incorporated at the N-terminus is always methionine (or fMet).
- Glycine and Proline are incorporated at subsequent internal positions based on the mRNA sequence.
- Thymine is a nitrogenous base found in DNA, not an amino acid.
Step 3: Final Answer:
The amino acid that starts protein synthesis in all organisms is Methionine.
Therefore, the correct option is (B).
Translation is the process by which ribosomes synthesize proteins using an mRNA template.
The initiation of translation is a highly conserved molecular event guided by specific start codons and initiator tRNAs.
Step 2: Detailed Explanation:
In both prokaryotes and eukaryotes, the universal start codon on the mRNA transcript is AUG.
- This codon is recognized by a specialized initiator transfer RNA (tRNA).
- In eukaryotes, the AUG start codon recruits an initiator tRNA carrying the amino acid Methionine.
- In prokaryotes, plastids, and mitochondria, the initiator tRNA carries a modified form of this amino acid, known as N-formylmethionine (fMet).
During polypeptide chain elongation, the first amino acid incorporated at the N-terminus is always methionine (or fMet).
- Glycine and Proline are incorporated at subsequent internal positions based on the mRNA sequence.
- Thymine is a nitrogenous base found in DNA, not an amino acid.
Step 3: Final Answer:
The amino acid that starts protein synthesis in all organisms is Methionine.
Therefore, the correct option is (B).
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