Biochemistry - I. II. III. IV. Carbohydrates Lipids...

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I. Carbohydrates II. Lipids III. Proteins IV. Nucleic Acids Biochemistry is the study of the chemicals of living systems and their interactions. Alone, these chemicals are not living, but together, their interactions work together to create and sustain a living organism. The reactions between them obey all of the known laws of chemistry. To sustain a living system, materials, energy, and information is needed. The substances that supply these three necessities are the basic materials which, together with water and a few kinds of ions, make up cells and tissues. Proteins are the main source of the materials. Lipids and carbohydrates are the major sources of the chemical energy needed to maintain function. And information is carried in a genetic code by molecules of nucleic acid Carbohydrates: Carbohydrates are naturally occuring polyhydroxyaldehydes or polyhydroxyketones, or they are compounds that react with water to give these compounds. They include sugars, starches, cellulose, and similar substances. Monosaccharides Carbohydrates that are unable to react with water and usually are the units making up larger carbohydrates are called monosaccharides . The most common is glucose, a pentahydroxyaldehyde, and it is the most widely occuring structural unit in the entire living world. It is the builing unit for many important polysaccarides such as cellulose and starch. Fructose, a pentahydroxylketone, is another monosaccharide that makes sugar (sucrose) when combined with glucose. CH 2 -CH-CH-CH-CH-CHO | | | | | OH OH OH OH OH glucose (open-chain form) CH 2 -CH-CH-CH-CO-CH 2 | | | | | OH OH OH OH OH fructose (open-chain form) The open-chain forms account for less than 0.1% of all the molecules. Monosaccharides usually come in cyclic forms. Cyclic Forms of Monsaccharides When dissolved in water, molecules of carbohydrates exist in equilibrium involving more than one structure. Glucose, exists as two cyclic forms and one open chain form (rare) in
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water. The equilibrium shifts to supply more of any of its members when a specific reaction occurs to only one. Galactose, another monosaccharide, differs by the projection of the OH group at carbon 4 (far left carbon in ring). Disaccharides Disaccharides are carbohydrates composed of two monosaccharide molecules. They are created through dehydration synthesis (removal of water) and broken apart through hydrolysis (addition of water). For example, these are molecules of sucrose and lactose: glucose + fructose ==> sucrose + H 2 O galactose + glucose ==> lactose + H 2 O The above structures both come in cyclic forms and are linked through oxygen bridges. Polysaccharides Polymers of of carbohydrates are called polysaccharides, and make up some of the most inportant naturally occurring compounds. They have thousands of monosaccharide units
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linked to each other by oxygen bridges. They incluse starch, glycogen, and cellulose, all three of which yield only glucose when completely hydrolyzed. Starch occurs naturally in plants, which use it to store glucose units for energy. It is often
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Biochemistry - I. II. III. IV. Carbohydrates Lipids...

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