Proteins (also called polypeptides) are large biological molecules which consists of one or more chains of amino acid. Proteins perform a series of functions which are catalysing metabolic reactions, DNA replication, providing structure to cells, transport molecules from one location to another within an organism etc.
Collagen consists of amino acids bound together to form a triple helix of elongated fibrils. It can be found in the skin, ligaments etc.
Enzymes are globular protein molecules which have the tertiary structure. They are generally rounded, "squashed" ball shape. Others include fibrous proteins which are long thin structures and are found in muscles and hair.
