Along with carbohydrates and fats, proteins are macronutrients of the organism. They are macromolecules composed of carbon, hydrogen, oxygen and nitrogen. Many of them also contain sulfur and phosphorus. They are formed by amino acids joined by peptide bonds. Proteins constitute approximately 50% of the dry weight of the tissues and practically involved in the biological processes of the Agency. The main functions of the proteins are: are essential for growth. They provide essential amino acids essential for the synthesis of tissue.

They are the raw material of digestive juices, hormones, haemoglobin, enzymes, vitamins, etc. Hemoglobin carries out the transport of gases such as oxygen and carbon dioxide in blood. Enzymes act as catalysts biological to accelerating the speed of chemical reactions of the metabolism. They act as a defence, antibodies are proteins of natural defence against infections or foreign agents. Collagen is the component main supporting tissues. They allow cell movement through the myosin and actin (muscle contractile proteins).

Energy intake, the proteins bring to the body 4.4 calories (kcal) of energy per gram. Proteins are classified according to their chemical structure in: simple: produce only amino acids to be hydrolyzed. Albumins and globulins: soluble in water and dilute salt solutions. Glutelinas and prolaninas: soluble in acids and alkalis. Gluten is formed from a mixture of glutenins and gliadins with water. Derived proteins: are the product of hydrolysis. Albuminoids: Insoluble in water, are fibrous, include keratin, collagen and fibrin. Conjugated proteins: are those which contain no protein parts, for example the nucleoproteins. In metabolism, the main end product of the proteins is ammonia which is converted into urea in the liver and is excreted through urine. Essential and non-essential amino acids. Proteins are composed of hundreds or thousands of amino acids. Amino acids are divided into essential and non-essential amino acids. The essential ones are those that are not produced by our body and need to be incorporated through the diet. Non-essential can be synthesized by our body. They are essential amino acids: phenylalanine, isoleucine, Leucine, methionine, lysine, threonine, valine, and tryptophan. And during childhood and adolescence also: arginine and Histidine. They are the non-essential amino acids: alanine, PROLINE, cysteine, glycine, hydroxyproline, cystine, serine, tyrosine, aspartic acid, and glutamic. The nutritional quality of a protein depends on its content in essential amino acids, which is measured by an index called biological value. The proteins of animal origin have a biological value more than vegetable origin. Foods that provide protein of high biological value are all of animal origin: all meat, eggs and fish crustaceans and shellfish. The milk and all dairy foods that bring us protein incomplete, are all vegetable source: legumes soy cereals and their derivatives dried fruits fruits and vegetables in any case the daily diet should contain both animal and vegetable proteins in a proportionate way, since our body uses amino acids that compose those proteins. However it is very important not to neglect the intake of proteins of animal origin, which are those that contain essential amino acids that our body can not synthesize.

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