Biological catalysts that accelerate chemical reactions in living organisms are known as enzymes. Their primary constituent is protein. Certain enzymes necessitate the assistance of non-protein entities, termed cofactors or coenzymes, for their operational capacity. Nevertheless, the fundamental framework of an enzyme is derived from proteins, which are themselves assembled from amino acids. - While carbohydrates, lipids, and nucleic acids fulfill other crucial cellular functions, they do not characteristically operate as enzymes. Consequently, the accurate selection is option (A) Proteins.