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BCH-2 Carbohydrates

BCH-2 Carbohydrates - Carbohydrates Carbohydrates Over Over...

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Carbohydrates square6 Over half of the organic carbon on the planet is stored as polymers of glucose - starch or cellulose. Humans can hydrolyze starch for energy, but only a few organisms produce the enzyme cellulase, needed to hydrolyze cellulose. square6 The general formula for sugars is CH 2 O. Sugars are composed of monosaccharides, oligosaccharides and polysaccharides. Typical polysaccharides like glycogen found in animals, while starch and cellulose are found in plants. Carbohydrates are a major source of energy and they are a major component of cell walls of plants and bacteria.
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Structure and Stereochemistry Monosaccharides are either aldoses (polyhydroxy aldehydes) or ketoses (polyhydroxy ketones). The simplest sugars are trioses: glyceraldehyde and dihydroxyacetone. Stereochemically glyceraldehydes can be either D or L. The most abundant sugars are the hexoses. Also very important are two pentoses: ribose and deoxyribose found in RNA and DNA. The side that the hydroxyl group is on at the chiral carbon (carbon 2 in glyceraldehyde and carbon 5 in glucose) determines whether it is D- [to the right] or L- [to the left]. You should try to learn about the different names associated with isomers of sugars.
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Cyclic Structure Anomers Five and Six carbon sugars tend to have cyclic structures rather than straight chains. Aldohexoses form hemiacetals and ketohexoses for hemiketals. The carbonyl carbon becomes a new chiral center called the anomeric carbon . In the glucopyranose form α -D sugar has the hydroxyl group facing down and the β -D sugar has the hydroxyl group facing up. In nature only the β -D anomers of ribose and deoxyribose are found in RNA and DNA.
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