Fundamentals of Human Nutrition/Amino acids

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12.2 Amino AcidsEdit

Amino acids are the monomers of proteins and are an essential part of human growth, development, and health. There are a total of twenty amino acids, with Asparagine being the first to be discovered in 1806. Amino acids are all composed of a carboxyl group, an amino group, and a hydrogen atom bonded to the same carbon atom-the alpha carbon (Basic Structure, 2003). They differ from one another in their side chains, or the R groups bonded to the alpha carbon. The R groups of the different amino acids can differ in size and structure, as well as electric charge (acidic or basic), which influences the solubility of the amino acids in water (Nelson and Cox, 2013).

There twenty amino acids that are generally found in proteins, and they are: Glycine, Alanine, Valine, Isoleucine, Leucine, Proline, Methionine, Phenylalanine, Tyrosine, Tryptophan, Serine, Cysteine, Threonine, Asparagine, Glutamine, Aspartic acid, Glutamic acid, Histidine, Lysine, and Arginine. Proteins are broken down using hydrolysis reactions in which a water molecule is added to the protein, and this results in individual amino acids being formed. Proteins are synthesized using dehydration reactions (condensation reaction), in which a molecule of water is removed and a peptide bond forms between the amino acids. When two amino acids are joined together, the resulting molecule is called a dipeptide. When three are joined together, the molecule is called a tripeptide (Whitney and Rolfes, 2015). As a chain of many amino acids forms and grows, the chain is called a polypeptide.

The human body needs and uses the different amino acids to make proteins to help the body: 1) Metabolize food, 2) Repair torn or damaged body tissues, 3) Grow, and 4) Perform other important body functions (Amino acids, 2013).

The twenty amino acids are separated into three groups: 1) Essential amino acids, 2) Nonessential amino acids, and 3) Conditional Amino Acids. Essential amino acids are the amino acids that the body cannot synthesize by itself or cannot make in adequate quantities. Instead it must get these amino acids through food obtained in the diet. There are a total of nine essential amino acids. These are: Valine, Isoleucine, Leucine, Threonine, Histidine, Lysine, Phenylalanine, and Tryptophan. The nonessential amino acids are those that the body can synthesize by itself and make in large enough quantities. There are 11 nonessential amino acids and they can be supplied by food in the diet but it is not a requirement. Nonessential amino acids can be produces as long as there is a supply of Nitrogen to produce the amino group of the amino acid and pieces of fat or carbohydrates to form the rest of the structure. Conditional amino acids are amino acids that are usually nonessential but become essential during times of stress, illness, or other special circumstances. One such illness is Phenylketonuria, an inherited disease in which the nonessential amino acid tyrosine becomes essential because the body cannot convert phenylalanine into tyrosine (Whitney and Rolfes, 2015).

There are several foods that one should eat to obtain all essential amino acids. These foods include: beans, chicken, lean meat, fish, nuts and seeds, peanut butter, tofu, lentils and many others (Protein in diet, 2013).

Citations: 1) Amino acids: MedlinePlus Medical Encyclopedia. (2013, February 18). Retrieved October 4, 2015. 2) Whitney, E., & Rolfes, S. (2015). Proteins. In Understanding Nutrition (14th ed., p. Chapter 6). 3) Proteins, Peptides & Amino Acids. (2013, May 5). Retrieved October 4, 2015. 4) Nelson, D., & Cox, M. (2013). Amino Acids, Peptides, and Proteins. In Lehninger principles of biochemistry (6th ed., pp. 76-77). New York: W.H. Freeman and Company. 5) Protein in diet: MedlinePlus Medical Encyclopedia. (2013, April 30). Retrieved October 4, 2015. 6) Basic Structure of an Amino Acid. (2003, August 25). Retrieved October 4, 2015.

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12.2.1 GlucogenicEdit

12.2.2 KetogenicEdit

12.2.3 UreaEdit