Protein Roles, Structural, Functional + Amino Acid Products, Epinephrine, Serotonin, Norepinephrine, Thyroid hormone, Bile,

   «Previous     Next»    Back to Index

What role do proteins play in the human body?

Much of structure and function of our body is based on proteins. Thus, protein and individual amino acids must function in our body in a number of ways. For instance, proteins can function as: enzymes (regulate chemical reactions), structural proteins (yield form to cells and tissue), contractile proteins (provide basis for muscle contraction), antibodies (help protect us from foreign entities), transport proteins (help transport substances in our blood), protein hormones (i.e., insulin, glucagon, and growth hormone), clotting factors (allow our blood to clot to stop a hemorrhage), and receptors on cells (allow hormones and neurotransmitters to function).

Individual amino acids can be used to make certain hormones and neurotransmitters such as epinephrine, serotonin, norepinephrine, and thyroid hormone (see Amino Acid Products Table). In fact, most neurotransmitters are derived from amino acids. Amino acids are also used to make other important substances such as creatine, choline, carnitine, nucleic acids, and the vitamin niacin. Last, amino acids can be used by some tissue as an energy source or can be converted to glucose or fat depending upon our current nutritional/metabolic state (i.e., fasting, fed, exercise).

What foods contain protein?

Because protein is vital to life, all life forms will contain protein; however, the protein content will vary. In general, foods of animal origin will have greater protein content than plants and plant-derived foods (see Table 6.3). Among the foods that have the highest protein content (percent of calories) are water-packed tuna and egg whites. Being an animal, tuna (and other fish) contain skeletal muscle for locomotion. Thus, eating finned or shellfish provides protein sources that are fairly similar to human skeletal muscle proteins. Meanwhile, the predominant protein in egg whites is albumin (e.g., ovalbumin and conalbumin) and ovomucoid, globulins and lysozymes. Another popular protein sources with this group, because of their protein density, is milk. The principal proteins in milk are caseins and whey, which are actually families of related proteins.

Cereal grains produce a vast array of proteins (including albumins); however, the most interesting proteins may be gliadin and glutenin. When these proteins are mixed with water, such as when we make dough, gluten is formed. Gluten provides the structural basis for the network that traps gases produced by yeast when dough rises. Soy lacks these proteins, and ingredients need to be added to soy flour to make it rise to a light bread. Gluten continues to be a topic of interest as many people either experience an allergy or intolerances to foods that contain it as detailed in Food & Supplements.

   «Previous     Next»    Back to Index