Question

In bacteria, the codon AUG stands for

• A. Glycine
• B. Methionine
• C. N-formyl methionine
• D. Both B and C

Answer 1

The correct option is D Both B and C

The process of translation i.e protein synthesis involves three processes- inititaion, elongation and termination. The synthesis of all proteins starts with the same amino acid: methionine. In eubacteria, the first amino acid in newly synthesized polypeptide is N-formylmethione. However formylation is not neccesary because non-formylated methionine can function as an initiator amino acid.

Eukaryotes and archaea also use methionine as an initiating amino acid, but it is not formylated methionine. In eubacteria, such as E.coli, AUG and GUG and on rare occasions UUG serve as initiation codons. When one of these triplets is present in the initiation position, it is recognized by N-formyl Met-t-RNA and N-formylmethionine appears as the first amino acid in the chain. The meaning of AUG and GUG codons depends on their context. When the AUG codon is used for initiation, it is read as formyl-methione; when used within the coding region, it represents methionine. Similarly when GUG codon serves as an initiation codon, it is read as formylmethionine. Initiation in the eukaryotic cytoplasm almost always uses AUG as the initiator.