Protein metabolism is the chemical process used by the body to break down dietary or endogenous proteins into amino acids. Ingested dietary proteins are digested into amino acids and absorbed into the bloodstream. These amino acids are then used to synthesize new proteins or can be used as an energy source. DNA carries the instructions for building cells and tissue. This information is expressed by combining specific amino acids into unique proteins.
The basic difference between protein and carbohydrate is that while carbohydrates are made out of simple sugars (carbon, hydrogen, and oxygen), protein is made from amino acids (carbon, hydrogen, oxygen, nitrogen, and sulfur). The nitrogen is a basic component of the protein's amino acids and accounts for 13 to 20% of the total mass.
The synthesis of a new protein requires the presence of all necessary amino acids. Amino acids have the same general structure with unique side chains determining the identity and function of each. They are much like letters in the alphabet that can be combined to form unique "words" or proteins. Non-essential amino acids can be produced by our bodies.
Proteins are needed to make, repair and maintain all tissues of the body. Proteins compose cells and they also help regulate cell function. Proteins function as enzymes used to speed up biological reactions. Protein can be used as an energy source, but it is not an efficient fuel like carbohydrates and fat.
Most authorities believe that the amount of protein converted to glucose is quite small, except under conditions of intense exercise or metabolic starvation. Under these conditions, amino acids produce the major source of glucose for blood sugar maintenance.