Proteins are the largest molecules in the body. Some scientists say that the main function of the cell is to produce proteins. Proteins make up 10-30% of the cells mass and can either be functional or structural molecules. Proteins are a class of complex nitrogenous compounds that are synthesized by all living organisms and yield amino acids when hydrolyzed. Proteins in the diet provide the amino acids necessary for the growth and repair of animal tissue. All amino acids contain carbon, hydrogen, oxygen and nitrogen and some also contain sulfur. About 20 different amino acids make up animal proteins, which may contain minerals such as iron or copper. A Protein consists of from 50 to thousands of amino acids arranged in a very specific sequence. The essential amino acids are those that the liver cannot synthesize (tryptophan, lysine, methionine, valine, leucine, isoleucine, phenylalanine, threonine, arginine and histidine); they are essential in the diet, and a protein containing them is called a complete protein. An incomplete protein lacks one or more of the essential amino acids. The nonessential amino acids are synthesized by the liver. Sources of amino acids in the diet are: Milk, eggs, cheese, meat, fish, and some vegetables such a soybeans are the best sources. Proteins are found in both vegetable and animal sources of food. Many incomplete proteins are found in vegetables; they contain some of the essential amino acids. A vegetarian diet can make up for this by combining vegetable groups that complement each other in their basic amino acid groups. This provides the body with complete proteins. Ingested proteins are the source of amino acids needed to synthesize the body’s own proteins, which are essential for growth of new tissue or the repair of damaged tissue, proteins are part of all cell membranes. Excess proteins in the diet may be changed to simple carbohydrates and oxidized to produce ATP. High levels of exercise, menstruation, pregnancy, lactation and convalescence from severe illness require increased protein intake. Excess protein in the diet results in increase nitrogen excretion in the urine. Amino acids are strung together through dehydration synthesis to form a complete protein. There are two classes of proteins in the body; fibrous and globular. In the next blog post we will look at the varied functions of both classes of proteins. Since dogs and cats are primarily carnivores it is important to know how proteins work in the body and what their daily requirements for proteins are. Once we are finished with discussing the basic nutritional elements we can begin to look at the sources of quality nutrients and how these nutrients enter into the body for use by the cells.