121lab02 - Laboratory 2 - Carbohydrates and Proteins...

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1 Laboratory 2 - Carbohydrates and Proteins Learning Objectives Students Will Be Able To: Identify the structural formula of simple sugars Differentiate between monosaccharides, disaccharides, and polysaccharides Identify the storage forms of carbohydrate in animals and plants Explain the process of oxidation and how it relates to human nutrition Identify the basic structure of an amino acid Differentiate between peptides, polypeptides, and proteins Explain the importance of dietary protein in human nutrition After reading these guidelines, students should be able to answer the following questions: What is a reducing sugar? What tests will be performed to test for reducing sugars, starches and proteins? What foods will be used? What color changes are expected for each of the tests? Introduction Part 1 (a and b): CARBOHYDRATES Carbohydrates are the major source of fuel (energy) in the average human diet. Carbohydrates supply approximately half of the total caloric intake in the typical American. There are two classes of carbohydrate, sugars and polysaccharides. Sugars include disaccharides - sucrose (table sugar), lactose (milk sugar), and maltose, and monosaccharides - glucose, (the most abundant monosaccharide in nature, and the most important nutritionally), fructose (fruit sugar), and galactose (which is found only as a component in lactose). Figure 1 shows the structural formula of glucose, maltose, and sucrose. Roughly half of dietary carbohydrate is supplied by sugars; the other half by polysaccharides. Polysaccharides are long chains of glucose units strung together. They include starch, the storage form of carbohydrate in plants, glycogen, the storage form of carbohydrate in animals (Figure 2), and some fibers.
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2 Figure 1 – Structural formula of glucose, maltose, and sucrose Carbohydrates are composed of carbon, hydrogen, and oxygen molecules. The energy contained in carbohydrates comes ultimately from the sun. In the presence of chlorophyll, the sun’s energy is used to bond six molecules of water (H 2 O) from the soil with 6 molecules of carbon dioxide (CO 2 ) from atmosphere. The end products are glucose (C 6 H 12 O 6 ) and oxygen. This reaction is called photosynthesis . Glucose molecules made by photosynthesis are linked together to form starch, the primary storage form of glucose in plants. When animals or humans consume the starch, the energy stored in chemical bonds of glucose is released to fuel metabolic reactions and voluntary activities. Glucose in excess of immediate needs is stored as glycogen (the primary storage form of glucose in animals) or triglycerides (fat). Figure 2 – Structural formula of glycogen The release of energy from glucose is accomplished by oxidation of glucose molecules that results in the loss of an electron . The electron is accepted by a nearby molecule in a reduction reaction. Reduction is one of the first steps in the
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3 sequence of reactions that ultimately releases the energy stored in glucose for use
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This note was uploaded on 01/16/2012 for the course NUTR 121 taught by Professor Heathergraham during the Fall '11 term at Truckee Meadows Community College.

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121lab02 - Laboratory 2 - Carbohydrates and Proteins...

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