Question

During elongation of polypeptide chain, sigma factor is

• A. Functionless
• B. Retained for specific function
• C. Released for re-use
• D. Required during closing of chain

Answer 1

The correct option is A Functionless

Elongation of nascent polypeptide occurs by covalent attachment of successive amino acid residues which are carried to the ribosome and correctly positioned by its tRNA. Elongation requires elongation factors which are cytosolic proteins. The binding of each incoming aminoacyl-tRNA and the movement of the ribosome along the mRNA are facilitated by the hydrolysis of GTP. RNA polymerase is the enzyme of transcription and synthesizes RNA using DNA template strand. It is a complex enzyme with five core subunits and a sixth sigma subunit which binds transiently to the core enzyme and positions it to promoters on the DNA. Thus sigma subunit is not involved in any step of polypeptide synthesis but during transcription. Thus, the correct answer is option A.