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| forms a six-sided ring, although in three-dimensions it forms a structure that looks a bit like a chair. The six carbon atoms are numbered as shown, so we can refer to individual carbon atoms in the structure. In animals glucose is the main transport sugar in the blood, and its concentration in the blood is carefully controlled. There are many isomers of glucose, with the same chemical formula (C6H12O6), but different structural formulae. These isomers include fructose and galactose. |
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| are formed when two monosaccharides are joined together by a glycosidic bond. The reaction involves the formation of a molecule of water (H2O |
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| is glucose 1-4 glucose. It is formed on digestion of starch by amylase, because this enzyme breaks starch down into two-glucose units. Used in brewing beer. |
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| is glucose 1-2 fructose. It is common in plants because it is less reactive than glucose, and it is their main transport sugar. It is the common table sugar that you put in your tea. |
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| is galactose 1-4 glucose. It is found only in mammalian milk, and is the main source of energy for infant mammals |
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| long chains of many monosaccharides joined together by glycosidic bonds |
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| the plant storage polysaccharide. It is insoluble and forms starch granules inside many plant cells. Being insoluble means starch does not change the water potential of cells, so does not cause the cells to take up water by osmosis (more on osmosis later). It is not a pure substance, but is a mixture of amylose and amylopectin. |
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| Is simply poly-(1-4) glucose, so is a straight chain. In fact the chain is floppy, and it tends to coil up into a helix. |
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| is poly(1-4) glucose with about 4% (1-6) branches. This gives it a more open molecular structure than amylose. Because it has more ends, it can be broken more quickly than amylose by amylase enzymes. |
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| is similar in structure to amylopectin. It is poly (1-4) glucose with 9% (1-6) branches. It is made by animals as their storage polysaccharide, and is found mainly in muscle and liver. Because it is so highly branched, it can be mobilised (broken down to glucose for energy) very quickly. |
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| is only found in plants, where it is the main component of cell walls. It is poly (1-4) glucose, but with a different isomer of glucose. Starch and glycogen contain a-glucose, in which the hydroxyl group on carbon 1 sticks down from the ring, while cellulose contains b-glucose, in which the hydroxyl group on carbon 1 sticks up. This means that in a chain alternate glucose molecules are inverted. |
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| Chitin (poly glucose amine) |
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| found in fungal cell walls and the exoskeletons of insects |
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| Pectin (poly galactose uronate) |
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| found in plant cell walls. |
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