Enzymes, some hormones, and structural molecules like keratin and collagen are examples of .

Protein molecules.

Explanation:

Protein, highly complex substance that is present in all living organisms. A chain of amino acid residues is called a polypeptide which is a bond form by the carboxylate ion on one end and the -Nh2 on the other end via condensation reaction.

Proteins are large biological molecules (macromolecules), which consists of one or more long chains of amino acid residues. Proteins perform certain functions in organisms like Enzymes - catalysing metabolic reactions, DNA replication, responding to stimuli, providing structure to cells, transporting molecules from one location to another etc.

Proteins differ from one another in their amino acid sequence, which is dictated by the nucleotide sequence of their genes, which usually results in protein folding into a three-dimensional structure that determines its activity.