Proteins are large, complex molecules made up of smaller units called amino acids.

Here's a breakdown:

* Amino acids: There are 20 different amino acids that are commonly found in proteins. Each amino acid has a central carbon atom bonded to:

* An amino group (-NH2)

* A carboxyl group (-COOH)

* A hydrogen atom (-H)

* A side chain (R group): This is the unique part of each amino acid, giving it its specific properties.

* Polypeptide chains: Amino acids link together to form long chains called polypeptide chains. These chains are held together by peptide bonds, which are formed between the carboxyl group of one amino acid and the amino group of the next.

* Protein structure: Polypeptide chains fold into complex three-dimensional shapes, determined by the sequence of amino acids and interactions between them. These shapes are crucial for the protein's function.

In summary, proteins are essentially chains of amino acids linked by peptide bonds, folded into specific shapes.