Final answer:
The correct answer is option A. siRNA is not required for the synthesis of proteins; instead, it regulates the expression of genes by interfering with mRNA. mRNA, tRNA, and rRNA are necessary for protein synthesis.
Step-by-step explanation:
The process of protein synthesis involves several types of RNA, each with a specific role. mRNA (messenger RNA) is a single-stranded transcript of DNA that carries the genetic information from DNA to the ribosome, where the protein is synthesized. rRNA (ribosomal RNA) is a component of ribosomes, which ensures the proper alignment of mRNA and catalyzes the formation of peptide bonds between amino acids. tRNA (transfer RNA) carries specific amino acids to the ribosome to be added to the growing polypeptide chain.
However, siRNA (small interfering RNA) is not directly involved in the synthesis of proteins. Instead, it plays a role in the regulation of gene expression by interfering with the expression of specific mRNA strands. This regulatory process does not contribute to the actual assembly of protein molecules.
Therefore, the RNA not required for the synthesis of protein is siRNA.