The answer is B. Amino acids.
Proteins are made up of amino acids, which are linked together by peptide bonds. Amino acids are small organic molecules that contain a central carbon atom bonded to an amino group, a carboxyl group, a hydrogen atom, and a variable side chain. The side chain is what distinguishes one amino acid from another.
There are 20 different amino acids that are commonly found in proteins. The order in which the amino acids are linked together is called the primary structure of the protein. The primary structure of a protein determines its three-dimensional shape, which is called its tertiary structure. The tertiary structure of a protein is responsible for its function.
Proteins play a variety of important roles in the body. They are involved in metabolism, cell signaling, and immunity. Proteins are also essential for building and repairing muscle tissue.
Disaccharides, nucleotides, and fatty acids are not the molecules that link together to form proteins. Disaccharides are two sugar molecules linked together. Nucleotides are the building blocks of DNA and RNA. Fatty acids are the building blocks of lipids.