Amino acids are organic molecules that contain an amino group (-NH2) and a carboxyl group (-COOH). They are the building blocks of proteins, which are large biomolecules that are essential for the structure, function, and regulation of the body's tissues and organs. There are 20 common amino acids that are found in proteins, and they can be divided into three categories: essential amino acids, which cannot be synthesized by the body and must be obtained from the diet; non-essential amino acids, which can be synthesized by the body; and conditional amino acids, which are essential under certain circumstances, such as during periods of illness or stress.

Amino acid derivatives are compounds that are derived from amino acids. They can be synthesized from amino acids through chemical reactions that modify the structure of the amino acid molecule. Amino acid derivatives can be classified according to the type of chemical reaction used to synthesize them, such as esterification, acetylation, and amidation.

Some examples of amino acid derivatives include:

1. Peptides: These are short chains of amino acids that are linked together by peptide bonds (-CO-NH-). Peptides are intermediate-sized molecules that are found in many biological systems, including hormones, enzymes, and neurotransmitters.

2. Proteins: These are large biomolecules that are made up of long chains of amino acids. Proteins play many important roles in the body, including providing structural support, catalyzing chemical reactions, and regulating biological processes.

3. Nucleotides: These are compounds that are composed of a nucleoside (a nitrogenous base, a sugar, and a phosphate group) and one or more phosphate groups. Nucleotides are the building blocks of nucleic acids, such as DNA and RNA, which carry genetic information.