What is the chemical composition of proteins?

Proteins are complex macromolecules composed of smaller building blocks called amino acids. The chemical composition of proteins consists of carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur. The basic structure of an amino acid includes an amino group (-NH2), a carboxyl group (-COOH), a hydrogen atom, and a unique side chain or "R" group. The side chain varies among different amino acids, giving each amino acid its distinct properties.

When amino acids are joined together through peptide bonds, they form a polypeptide chain, which then folds into a specific three-dimensional structure to create a functional protein. The sequence of amino acids along the polypeptide chain determines the protein's unique shape and function.

There are 20 common amino acids that make up proteins, and they can be classified into different groups based on the properties of their side chains:

Nonpolar, aliphatic amino acids: Glycine, Alanine, Valine, Leucine, Isoleucine, Methionine, Proline.
Aromatic amino acids: Phenylalanine, Tyrosine, Tryptophan.
Polar, uncharged amino acids: Serine, Threonine, Cysteine, Asparagine, Glutamine.
Positively charged (basic) amino acids: Lysine, Arginine, Histidine.
Negatively charged (acidic) amino acids: Aspartic acid, Glutamic acid.
The unique arrangement and interaction of these amino acids within a protein's three-dimensional structure determine its function. Proteins have diverse roles in living organisms, including enzymes, structural components, signaling molecules, transporters, antibodies, and more.