Which RNA type is primarily involved in the synthesis of proteins?

Messenger RNA (mRNA) plays a crucial role in the synthesis of proteins. It serves as the primary template transcribed from DNA during the process of gene expression. Once synthesized, mRNA carries the genetic information from the nucleus to the ribosomes, where translation occurs. The ribosomes read the sequence of nucleotides in the mRNA and translate it into a specific polypeptide or protein by matching codons in the mRNA with the appropriate amino acids brought by transfer RNA (tRNA).

In contrast, heterogeneous nuclear RNA (hnRNA) is an early precursor of mRNA that undergoes various modifications, such as splicing, before becoming mature mRNA. MicroRNA plays a regulatory role by binding to mRNA molecules and can inhibit protein synthesis, but it is not directly involved in the synthesis itself. Small nuclear RNA (snRNA) is involved in the splicing process of pre-mRNA but does not directly contribute to protein synthesis either. Thus, mRNA is the specific type of RNA whose primary function is to direct the synthesis of proteins.