Proteins are long chains of amino acids connected through a peptide bond that results in the loss of a water molecule. Peptides are small proteins made up of approximately 2 to 100 amino acids. Amino acids have a common core with variable side chain groups (R).

The 20 natural amino acids have R groups that can be hydrophobic, hydrophilic, basic, or acidic. Proteins undergo secondary structure transformations by twisting and turning to obtain a conformation that minimizes surface tension. This makes the shape of proteins/peptides much more complicated and unique than DNA that exists in a more rigid double helix. The highly reactive hydrophilic amino acids can be positioned in the protein/peptides sequence from the sequence of the DNA. Also, hydrophilic residues tend to be found on the outside of the peptide structures. Together these factors permit proteins to be effective and selective enzymes in the body.

Some diseases result from mutated forms of proteins/peptides resulting from either mutated DNA or improper protein folding. Peptide drugs have become more popular with the aid of new technology such as X-ray crystallography and computational atomic modeling that permit better peptide drug leads. Recent advances in peptide drugs permit them to be taken orally, gaining wider acceptance. Many scientists are utilizing peptides to investigate cardiovascular disease, cancer, HIV/AIDS, hepatitis, multiple sclerosis and osteoporosis. Peptide drugs can act as hormones for control of osteoporosis or glucagen for the treatment of hypoglycemia. Others can block hormone binding to receptors, such as the peptide drug Lupron for prostate cancer and Sandostatin for growth abnormalities. Several common peptide drugs on the market are Zestril and Prinivil for hypertension, Calcitonin for Osteoporosis, Accolate for Asthma, and Integrilin for Anti-coagulation.

The main 20 amino acids