Protein Metabolism

Protein is composed of carbon, hydrogen, oxygen, nitrogen, and, in some cases, sulfur. Protein is the only nutrient that contains nitrogen, a fact that makes it both essential and potentially toxic. Amino acid building blocks constitute the larger molecular structures of protein. Some of these amino acids can be synthesized from other amino acids (referred to as nonessential amino acids), while some must be obtained from the foods we eat (referred to as essential amino acids). There is widespread confusion about essential and nonessential amino acids because the word nonessential suggests that, although they are present, they are not really needed. This, however, could not be further from the truth. Both the essential and nonessential amino acids are equally important (and therefore equally essential) in human metabolic processes.

Amino acids combine together to make much larger proteins. The sequence of the amino acids and the secondary and tertiary structures of the protein determine its function. When dietary protein is consumed, it is digested into polypeptides (small protein molecules) and eventually into individual amino acids. The amino acids are absorbed into the blood and transported to different tissues, where they are manufactured into necessary proteins. Tissues manufacture the proteins that are needed through the amino acids available to them. To ensure that the tissues are capable of manufacturing needed proteins, the essential amino acids must be present for protein synthesis to take place. Some people believe that if you want healthy looking hair and nails, you should consume the primary protein that hair and nails are made of (gelatin). Gelatin is a low-quality protein with a poor distribution of the essential amino acids, so it would not encourage an optimal protein synthesis. Put simply, eating hair and nails does not encourage optimal synthesis of hair and nails. The best way to ensure an optimal synthesis of needed proteins is to make all the essential amino acids available to cells so they are capable of making whatever they need.

Several amino acids have specific effects on the central nervous system . Because of these known effects, single amino acids have been sold with the purpose of imparting these known outcomes. Tryptophan, for instance, has been sold as an agent that causes relaxation or sleepiness. The dangers, however, of pushing high doses of single amino acids into the system are sufficiently large that this should not be done unless under the careful supervision of a physician. The best strategy is to supply the widest possible array of essential amino acids from food alone, which allows the individual tissues to synthesize the amino acids needed for optimal body function.

The liver is the central processing unit for protein synthesis, continually monitoring protein needs and synthesizing amino acids and proteins to satisfy a variety of needs. This protein synthesis is accomplished through transamination and deamination reactions. In transamination, the nitrogen from one amino acid is used for the manufacture of another amino acid; in deamination the amino group is removed from an amino acid and converted to ammonia . The remaining carbon structure is either reconstructed as fat and stored, converted to glucose (as happens with the amino acids alanine and glutamine), or burned for energy. Once all protein needs are met, the fate of all remaining amino acids is deamination. The ammonia created during deamination is toxic to the body, but enzymes in the liver convert the ammonia to urea. Urea is excreted from the body in the urine. Therefore, the greater the extra protein consumed, the greater the production of ammonia that must be removed from the system (as urea). The majority of the remaining deaminated carbon chains are typically stored as fat.