What does RNA polymerase do during transcription?

During transcription, RNA polymerase plays a crucial role in synthesizing RNA by adding ribonucleotides to a growing RNA strand. This process involves the enzyme unwinding the DNA double helix and reading the template strand to produce a complementary strand of pre-mRNA. As it moves along the DNA, RNA polymerase catalyzes the formation of phosphodiester bonds between the ribonucleotides, resulting in the formation of a single-stranded RNA molecule that is complementary to the DNA template. This pre-mRNA strand ultimately serves as the precursor to mature messenger RNA (mRNA) after further processing, which is essential for the expression of genes into proteins. Thus, the central function of RNA polymerase during this phase of gene expression is accurately captured by the notion that it builds pre-mRNA from nucleotides.