Proteins (translated from Greek: "first thread") are the basis of structure and function in all living things. It is a complex, molecularly heavy organic compound consisting of amino acids joined by peptide bonds; they are frequently called polypeptides for this reason. Proteins have numerous functions in organisms, including:
- Enzymes or subunits of enzymes
- Structure and mechanics, such as cytoskeletal joints or muscles
- Immune response
- Storage and transport of ligands
Proteins are encoded by DNA; RNA is transcribed from DNA, and proteins are built on the RNA template by ribosomes.
A protein's unique 3-dimensional folded structure is called its native state; the folding and unfolding of proteins are a large part of what allows it to function. They are amazingly complex, and biologists must describe them in four different ways: the primary structure, or amino acid sequence, held together with covalent peptide bonds; secondary structure, or highly-patterned subunits, held together with hydrogen bonds; tertiary structure, or its shape, primarily held together by hydrophobic interactions; and quaternary structure, or the shape resulting when multiple protein molecules bond together to form a larger structure. The process by which the tertiary and quaternary structures form is called protein folding.
The level of a protein's structure often defines its purpose; for instance, a protein that lacks tertiary structure will probably act as a hormone; one with tertiary structure usually acts as an enzyme.
Web Resources On Proteins
Protein Information Resource
Book Resources On Proteins
Proteins : Structures and Molecular Properties by Thomas E. Creighton
Introduction to Protein Structure by Branden & Tooze