What term describes an RNA molecule that can function as an enzyme?

The correct answer is ribozyme. A ribozyme is a specific type of RNA molecule that exhibits catalytic activity, meaning it can accelerate chemical reactions, similar to how enzymes do. This characteristic distinguishes ribozymes from standard RNA, which primarily serves as a messenger between DNA and protein synthesis but does not have enzymatic functions.

Ribozymes can participate in various biological processes, such as RNA splicing and the catalysis of peptide bond formation during protein synthesis in the ribosome. Their ability to act as enzymes underscores the fundamental role of RNA in biological systems, particularly in processes central to life.

Other choices, such as a ribosome, RNA polymerase, and helicase, refer to different structures or proteins involved in biological processes. Ribosomes are the cellular machinery that synthesizes proteins, RNA polymerase is an enzyme responsible for synthesizing RNA from a DNA template, and helicase is an enzyme that unwinds DNA strands during replication. While these are essential for various cellular functions, none of them function as RNA molecules or possess catalytic activity like ribozymes do.