The Importance Of Amino Acids

5. The Importance Of Amino Acids

Many different proteins are known, but all of them are constructed from 23 principal amino acids. These amino acids are the building blocks of all vegetable and animal protein. A molecule of protein may contain as many as several hundred or even thousands of these amino acids. These amino acids are linked together within the protein molecule in a unique fashion known as peptide linkage. A specific protein contains a variety of amino acids linked together in a sequence specific to that protein.

The body cannot use or assimilate protein in its original state as eaten. The protein must first be digested and split into its component amino acids. The body can then use these amino acids to construct the protein it needs. The ultimate value of a food protein, then, lies in its amino acid composition. It is the amino acids that are the essential nutrients. The proper study of the role of protein in nutrition can only be done with a thorough understanding of the amino acids.

5.1 Sources of Amino Acids

5.1.1 Exogenous Protein

Amino acids are the end products of protein digestion. When protein is eaten, enzymes in the stomach and small intestine begin to break the linkages within the protein molecule and produce shorter and shorter chains of amino acids. Eventually, the amino acids are in a simplified enough chemical form so that they can pass through the intestinal walls into the bloodstream. They are then carried by the portal vein to the liver for elaboration and passed on to the blood, lymph and cells. The cells synthesize the amino acids into proteins as required.

This simplified description of the digestion and assimilation of protein applies to exogenous protein. Exogenous protein is the term for protein obtained through the diet or from outside of the body.

5.1.2 Endogenous Protein

Protein may also be obtained from within the body. This is called endogenous protein. Endogenous protein does not come directly from the foods we eat, but from the synthesis of proteins from within the body.

Obtaining protein from the diet is common knowledge. The fact that the body can synthesize protein from its own proteinaceous wastes, however, is not widely known.

As the body’s cells undergo their natural catabolic processes, they produce proteinaceous wastes in the form of spent cells and other by-products of their own metabolism. These proteinaceous products enter the lymph fluid.

Other cells in the body are able to ingest these spent proteins and to digest them in vesicles (“stomachs”) of their own formation. The body’s cells are thus able to break these proteinaceous wastes down into amino acids and use them to synthesize their own protein.

Endogenous protein (or protein from within the body) is an important source of amino acids that is often overlooked by conventional nutrition writers. Many times, up to two-thirds of the body’s total protein needs are supplied through endogenous protein and not from exogenous dietary sources.

5.2 The Amino Acid Pool

From the digestion of proteins in the diet and from the recycling of proteinaceous wastes, the body has all the different amino acids circulating in the blood and lymphatic system. When cells need these amino acids, they appropriate them from the blood or lymph. This continually-circulating available supply of amino acids is known as the amino acid pool.

The amino acid pool is like a bank that is open twenty-four hours. The liver and the cells are continually making deposits and withdrawals of amino acids, depending upon the concentration of amino acids in the blood.

When the number of amino acids is high, the liver absorbs and stores them until needed. As the amino acid level in the blood falls due to withdrawals by the cells, the liver deposits

some of the stored amino acids back into circulation.

The cells also have the capacity to store amino acids. If the amino acid content of the blood falls or if some other cells require specific amino acids, the cells are able to release their stored amino acids into circulation. Since most of the body’s cells synthesize more proteins than are necessary to support the life of the cell, the cells can reconvert their proteins into amino acids and make deposits into the amino acid pool.

Between the deposits and withdrawals by the liver and cells, there is a continual flux of amino acids in the blood and plasma. This circulating source of amino acids, as well as the potential availability of the amino acids stored within the liver and the cells, makes up the important amino acid pool. This pool of amino acids is very important in understanding why complete proteins are not necessary in the diet and will be discussed later in this lesson.

5.3 The Specific Amino Acids and Their Functions

5.3.1 Specific Amino Acids—Descriptions and Sources

The following descriptions of the amino acids include their most important functions and some of the food sources in which they are found.

ALANINE — Is a factor in regulating the adrenal glands and insuring healthy skin, particularly the scalp. It is found in almonds, alfalfa sprouts, apples, apricots, avocadoes, carrots, celery, cucumbers, grapes, lettuces, oranges, strawberries, sweet peppers and tomatoes.

ARGININE — Is used in muscle contraction and the construction of cartilage. It is essential in the functioning of the reproductive organs and in controlling the degeneration of the body cells. Arginine is found in alfalfa sprouts, beets, carrots, celery, cucumbers, lettuces, parsnips, potatoes and turnips.

ASPARTIC ACID — Is used in cardiovascular functions and in the retarding of tooth and bone destruction. It is found in almonds, apples, apricots, carrots, celery, cucumbers, grapefruits, lemons, pineapples, tomatoes and watermelons.

CYSTINE — Is used in the formation of red blood corpuscles and is involved in hair growth and the functioning of the mammary glands. It is found in alfalfa sprouts, apples, brazil nuts, beets, brussels sprouts, cabbages, carrots, currants, cauliflower, filberts, kale, pineapples and raspberries.

GLUTAMIC ACID — Is used in maintaining blood-sugar levels. Anemia will not occur if this and other nutrients are obtained and used. Glutamic acid is also a factor in the secretion of gastric juices. It is found in brussels sprouts cabbages, carrots, celery, green beans, lettuces and papayas

GLYCINE — Is a factor in forming muscle fiber and cartilage and in regulating sex hormones. It is found in alfalfa sprouts, almonds, carrots, celery, okra, oranges, potatoes, pomegranates, raspberries, turnips and water melons.

HISTIDINE — Is used in manufacturing glycogen and in the control of mucus. It is a component of hemoglobin and semen. It is found in alfalfa sprouts, applet, beets, carrots, celery, cucumbers, endive, papayas, pineapples and pomegranates.

HYDROXYGLUTAMIC ACID — Is similar to glutamic acid and is a factor in controlling digestive juices. It is found in carrots, celery, grapes, lettuces, plums, raspberries and tomatoes.

HYDROXYPROLINE — Aids in liver and gallbladder functions, in emulsifying fats and in the formation of red blood corpuscles. It is found in almonds, apricots, avocadoes, brazil nuts, beets, carrots, cherries, cucumbers, coconuts, figs, grapes, lettuces, oranges, pineapples and raisins.

IODOGORGOIC ACID — Is a factor in all glandular functions. It is found in carrots, celery, lettuces, pineapples and tomatoes.

ISOLEUCINE — Aids in the regulation of the thymus, spleen, pituitary and the metabolism. It is also a factor in forming hemoglobin, lsoleucine is found in .avocadoes, coconuts, papayas, sunflower seeds and almost all nuts.

LEUCINE — Counterbalances the isoleucine amino acid and is found in the same food sources.

LYSINE — Aids in the functions of the liver, gallbladder and pineal and mammary glands. It is also a factor in fat metabolism and in preventing cell degeneration. Lysine is found in alfalfa sprouts, apples, apricots, beets, carrots, celery, cucumbers, grapes, papayas, pears and soybean sprouts.

METHIONINE — Aids in the functioning of the spleen, pancreas and lymph glands. It is a constituent of hemoglobin and tissues and is found in apples, brazil nuts, cabbages, cauliflower, filberts, kale and pineapples.

NORLEUC1NE — Balances the functions of leucine. Synthesized within the body if needed.

PHENYLALANINE — Is involved in the functions of the kidneys and bladder and in eliminating wastes. It is found in apples, beets, carrots, pineapples and tomatoes.

PROLINE — Involved in manufacturing white corpuscles and in the emulsifying of fats. It is found in apricots, avocadoes. almonds, beets, brazil nuts, carrots, cherries, coconuts, cucumbers, figs, grapes, oranges, pineapples and raisins.

SERINE — Aids in the tissue cleansing of the mucus membrane and in the lungs and bronchial. It is found in alfalfa sprouts, apples, beets, carrots, celery, cucumbers, cabbages, papayas and pineapples.

THREONINE — Aids in the balancing of amino acids. Threonine is found in alfalfa sprouts, carrots, green leafy vegetables and papayas.

THYROXINE — Involved with the activity of the thyroid, pituitary and adrenals and in metabolic functions. It is found in carrots, celery, lettuces, tomatoes and pineapples.

TRYPTOPHANE— Involved in the generation of cells and tissues and in the pancreatic and gastric juices. Tryptophane is also a factor in the optic system. It is found in alfalfa sprouts, beets, carrots, celery, green beans and turnips.

TYROSINE — Is a factor in the development of the cells and tissues and in the generation of red and white blood corpuscles. It is also found in the adrenals, pituitary, thyroid and hair. Food sources of this amino acid are alfalfa sprouts, almonds, apricots, apples, beets, carrots, cucumbers, cherries, figs, lettuces, sweet peppers, strawberries and watermelons.

VALINE — Involved in the functioning of the mammary glands and ovaries. It is found in apples, almonds, beets, carrots, celery, okra. pomegranates, squashes and tomatoes.

5.3.2 Functions of Amino Acids

We can say that, generally, the amino acids serve five functions in the body:

  1. They furnish the material from which proteins are synthesized by various cells.
  2. They are used by the cells in manufacturing enzymes, hormones and other nitrogenous products.
  3. They are used in constructing blood protein.
  4. They may furnish a source of energy, with some of the amino acids being transformed into glucose and glycogen.
  5. They aid the body in performing many functions as described in their individual descriptions.

5.4 Amino Acids—Essential and Non-Essential

5.4.1 Essential Amino Acids

Of the 23 amino acids, eight are termed essential. These are isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophane and valine. It is also said that a ninth amino acid, histidine, is essential for infants.

An “essential amino acid” is an amino acid that the body cannot produce by reduction (oxidation) from another amino acid. In other words, an essential amino acid must be found in a food source and cannot be produced within the body.

5.4.2 Non-Essential Amino Acids

The remaining 15 amino acids are termed “non-essential.” but this term is somewhat misleading. They are essential to our health and well-being, but it is not essential that they be present in the foods we eat (provided that there is an adequate supply of the essential amino acids in our diet).

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