Polypeptides are polymers composed of amino acids bound together by peptide bonds. Information in the messenger RNA determines the exact sequence of amino acids in a polypeptide.
Without polypeptides and their component amino acids, humans would not be able to survive. Peptide hormones control a variety of endocrine functions, from maintaining a normal glucose level to regulating the amount of calcium in the bloodstream. Growth hormone, thyroid-stimulating hormone, oxytocin and human chorionic gonadatropin are among the many peptide hormones found in the human body.
Humans also need amino acids to manufacture enzymes and structural proteins and to transport proteins. Proteins are essential for growth, tissue repair and metabolism. Although the human body produces some of its own amino acids, it doesn't produce all the amino acids necessary for survival. These amino acids are called essential amino acids because the body cannot manufacture them. Essential amino acids must come from protein-rich foods.
When a person consumes a protein-containing food, his digestive system uses enzymes called pepsin and trypsin to break it down. These enzymes break the bonds holding the amino acids together. The digestive system absorbs free amino acids and sends them to the bloodstream for circulation to other parts of the body.