Nutrition may be defined simply as the utilization of foods by living organisms for normal growth, reproduction, and maintenance of health. The compounds that are classed as nutrients include water, carbohydrates, proteins or amino acids, lipids, vitamins, and minerals. These nutrients make up living tissues whether they be plant, animal, or microbial tissues. Thus, these nutrients are obtained by intake of food and are then used by the human body to build and maintain its own tissues. The organic macronutrients are carbon compounds synthesized by living organisms. They include carbohy-drates, proteins or amino acids, and lipids. In the individual chapters in this unit on the structure and properties of the organic macronutrients, specific compounds in each class are described both from the viewpoint of dietary macronutrients and of organic compounds formed in the human body during metabolism of carbohydrates, proteins and amino acids, and lipids. The fourth group of organic nutrients, the vitamins, are micronu-trients and are considered in Unit V Organic macronutrients are required in large amounts and are sources of energy for the body
Like all organic compounds, proteins, carbohydrates, and lipids are made up largely of six elements: hydrogen, oxygen, carbon, and nitrogen along with some phosphorus and sulfur. These six relatively small elements with atomic weights :£ 32 make up the structure of proteins, carbohydrates, lipids, and vitamins as well as nucleic acids and intermediates of metabolism. If water (H20), which makes
Electron micrograph of starch granules in plant cells; courtesy of Cornell Integrated Microscopy Center, Cornell University, Ithaca, NY
up about 0:5"-. of Hit- human body, is not considered, carbon, oxygen, hydrogen, and nitrogen (in organic compounds} make up 88.5% of the "dry weight" of the human body; these elements ¿ire present in about 11 kg of protein, 10 kg of fat and O.fi kg of carbohydrate (mainly glycogen) in a 65-kg adult man.
The ability of carbon to form carbon-to-carbon bonds, extended carbon chains, and cyclic c ompounds permits the formation of a myriad of organic compounds; the structure of a number of these are considered in this unit. In organic molecules, the atoms of carbon, hydrogen, oxygen, phosphorus, and sulfur are held together by covalent bonds, which are formed when two atoms share a pair of outer orbital electrons. Kach covalent bond of every molecule represents a small amount of stored energy, allowing organic molecules to serve as a source of energy to the body. Units II, III. and IV describe the processes involved in the assimilation of dietary organic macromitrients. how these are used by the body for growth and maintenance? via synthesis of the structural and functional components of the human body, and how those macronutrients are used as fuels with conversion of excess substrate to stored fuels for subsequent use.
Martha H. Stipanuk
Structure and Properties of Carbohydrates
Classification, Structures, and Nomenclature of the Monosaccharides Classification
Structures of the Aldoses and Ketoses Cyclic and Conformational Structures Chemical Reactivity of the Monosaccharides General Reactivity of Sugars Formation of Glycosidic Linkages The Maillard Reaction of Reducing Sugars with Amines Other Classes of Carbohydrates Alditols
Glycuronic, Glyconic, and Glycaric Acids Deoxy and Amino Sugars
Their Properties Polysaccharides of Nutritional Importance General Characteristics Digestible Polysaccharides Nondigestible Plant Polysaccharides Natural and Modified Polysaccharides for Use in Processed Foods Glycoconjugates of Physiological Interest Glycosaminoglycans Proteoglycans Glycoproteins Glycolipids
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