List the key macromolecules, primary metabolites, and small molecules in metabolism.

Answer: The key macromolecules in metabolism are proteins (catalyzing reactions and providing structural support), nucleic acids (storing and transmitting genetic information), carbohydrates (providing energy and structural support), and lipids (energy storage, membrane structure, and signaling). Primary metabolites essential for cellular processes include glucose (energy source), amino acids (protein building blocks), fatty acids (lipid building blocks), and nucleotides (nucleic acid building blocks). Small molecules in metabolism, such as ATP (energy carrier), Coenzyme A (CoA, involved in fatty acid synthesis and oxidation), NAD+ (electron-carrier), and FAD (electron-carrier), play important roles as intermediates, substrates, and products of metabolic reactions.