MolecularBiologyandBiochemistryLecture2Summary -

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Carbohydrate chemistry : (CH2O)n or CxH2Oy Function: Available sugar: Can be digested/ absorbed and utilize by body (such as simple sugar and complex sugar (starch/ glycogen)) Unavailable carbohydrate: Insoluble fiber (laxative and lower absorption of fat/ cholesterol and lower risk of colon cancer) and soluble fiber (lower blood cholesterol by absorbing bile salt and reduce absorption of sugar and fat; also serve as food for colon microflora (which converts part of the fiber into short chain fatty acids and can produce vitamins (such as B12. K). Oligosaccharide such as FOS is a type of soluble fiber which is an important and healthy food ingredient. Structure: Monosaccharide:(CH2O)n where n =3to7(triose, tetrose, pentose(ribose),hexose,heptose) Fischer projection: a carbon skeleton and each carbon except one attached to hydroxyl (OH) group. The rest carbon (#1 or #2) is attached to a carbonyl group (aldehyde (aldose) or ketone (ketose) respectively). Any organic compound with a carbon atom attached to 4 different group exists as enantiomers (D isomer will turn plane polarized light to right) and the mirror image L isomer turn it to left). Majority of the sugar found in nature is D-sugar (identify by the chiral carbon with greatest number (farthest from carbonyl carbon) with the OH group point to right). Any two similar monosaccharides differ in only one chiral carbon = epimer, those differs in more than one chiral carbon but not all of them diastereomer). Haworth projection: Majority of the sugar in nature exist as ring structure (six member ring pyranose and five member ring furanose) rather than linear form. Ring structure is form when an OH group reacts with carbonyl carbon and turn into hemiacetal or hemiketal group. When drawing Haworth projection of sugar, those OH group point to the right points down in the ring. The rings can open and re-close, allowing rotation to occur about the carbon bearing the reactive carbonyl yielding two distinct configurations ( α  and  β of the hemiacetals and hemiketals. The carbon about which this rotation occurs is the anomeric carbon and the two forms are termed anomers. Carbohydrates can change spontaneously between the α  and  β configurations-- a process known as mutarotation.
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Acetal derivatives formed when a monosaccharide reacts with an alcohol in the presence of an acid catalyst are called glycosides. Cyclic Fischer Projection of α -D-Glucose Haworth Projection of α - D-Glucose Disaccharides: Covalent bonds between the anomeric hydroxyl of a cyclic sugar and the hydroxyl of a second sugar (or another alcohol containing compound) are termed glycosidic bonds, and the resultant molecules are glycosides. The linkage of two monosaccharides to form disaccharides involves a glycosidic bond. Polysaccharides: Starch
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This note was uploaded on 07/04/2011 for the course BIOC Point taught by Professor Point during the Spring '11 term at HKU.

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MolecularBiologyandBiochemistryLecture2Summary -

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