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Unicellular Organisms


Sugars Synthesis Carbohydrate is characterized by the presence of the atomic grouping H-C-OH, in which the ratio of H to O is approximately 2:1. Because water has this same ratio of hydrogen atoms to oxygen atoms, hence the name carbohydrate, which means hydrates of carbon, was given to them. If the number of carbon

Figure 11-08a Sugars

Figure 11-08b Synthesis and Hydrolysis of Polysaccharide [view large image]

atoms in a compound is low (from 3 to 7), then the carbohydrate is a simple sugar, or monosaccharide.

Larger carbohydrates are created by joining monosaccharides as shown in Figure 11-08b. Figure 11-08a shows a 5-carbon sugar called ribose, which is a component of RNA (deoxyribose has one less oxygen atom attached to the second carbon atom, hence the name DNA); and a 6-carbon sugar called glucose. The small numbers count the carbon atoms, which is important in specifying the carbon atom linkage (to other atom or group of atoms). Figure 11-08b shows the synthesis and hydrolysis (dissociation) of glucose. Polysaccharide is a carbohydrate that contains a large number of monosaccharide molecules (including glucose, fructose, and galactose). There are 3 polysaccharides that are common in organisms: starch, glycogen, and cellulose. Glucose is used as an energy source in cells. Starch and glycogen are storage form of glucose in plant and animal cells, respectively, and cellulose is found in plant cell walls. Naturally occurring sugars are all right-handed. Its mirrored version, i.e., the left-handed sugar can be produced artificially, but cannot be digested by living organism (making it a good but expensive dietary sugar). They are called chiral objects that cannot be superimposed on each other.

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