Question

During elongation of polypeptide chain, sigma factor is:
A. Functionless
B. Retained for the specific function
C. Released for re-use
D. Required during the closing of the chain

Answer 1

Hint: Sigma factors are bacterial RNA polymerases' subunits. They are in charge of determining the specificity of promoter DNA binding and controlling the efficiency with which RNA synthesis (transcription) begins.

Complete Step by Step Answer:
A polypeptide is an unbroken chain of amino acids linked together by peptide bonds. The peptide bond attaches the carboxyl group of one amino acid to the amine group of the following amino acid to form an amide.
The covalent connection of successive amino acid residues conducted to the ribosome and properly positioned by its tRNA results in the elongation of a nascent polypeptide. Elongation needs cytosolic proteins called elongation factors. The hydrolysis of GTP facilitates the attachment of each incoming aminoacyl-tRNA as well as the movement of the ribosome along the mRNA. RNA polymerase is a transcription enzyme that synthesizes RNA from a DNA template strand. It is a complex enzyme with five essential subunits as well as a sixth sigma subunit that binds to the core enzyme transiently and stances it to promoters on DNA. Thus, the sigma subunit is only involved in transcription and not in any other step of polypeptide synthesis. So, we can say that there is no use of the sigma factor during elongation of the polypeptide chain, hence regarding it as functionless.
The correct option is A.

Note: Transferring an amino acid from the first to the second tRNA may appear counter-intuitive at first. This makes sure that the original amino terminus of the first amino acid is never modified, and therefore the polypeptide "grows" in the amino carboxy terminus (NC).