Question

Given below are two statements: 
• [Statement (I):] The first amino acid in protein synthesis is Methionine in Eubacteria. 
• [Statement (II):] The first amino acid in protein synthesis is N-formyl-methionine in Archaea. 
In light of the above statements, choose the most appropriate answer from the options given below. 
 

• A. Both Statement (I) and Statement (II) are correct.
• B. Both Statement (I) and Statement (II) are incorrect.
• C. Statement (I) is correct but Statement (II) is incorrect.
• D. Statement (I) is incorrect but Statement (II) is correct.

Hint:

Remember the initiation differences across the domains of life:
- Eubacteria: Uses N-formylmethionine (fMet) as the first amino acid.
- Archaea and Eukaryotes: Use unmodified Methionine (Met) as the first amino acid.
This biochemical difference is often used as evidence of the evolutionary relationship between Archaea and Eukaryotes.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Translation (protein synthesis) begins at a specific start codon (typically AUG) on the mRNA transcript.
The initiator tRNA carries a modified or unmodified amino acid depending on the domain of life.

Step 3: Detailed Explanation:
Let us evaluate both statements:
- Statement (I) is incorrect: In Eubacteria (true bacteria), the initiator codon (AUG) recruits a specialized initiator tRNA charged with a modified amino acid called N-formylmethionine (fMet).
Therefore, the first amino acid in bacterial protein synthesis is fMet, not unmodified methionine.
- Statement (II) is incorrect: In members of the domain Archaea, as well as in Eukaryotes, the translation initiation machinery recruits an initiator tRNA charged with unmodified methionine (Met).
Archaea do not use N-formylmethionine to initiate protein synthesis.
Because the details of both statements are reversed, both Statement (I) and Statement (II) are incorrect.

Step 4: Final Answer:
Both Statement (I) and Statement (II) are incorrect, matching Option (B).