Carbohydrates: Structure and Function

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Introduction Carbohydrates are more than just fuels for the body and have other uses. Carbohydrates are hydrocarbons containing a carbonyl group and many alcohol groups. Their polymers can complex or they be simple and contain just one repeating monosaccharide, the roles of polymers can be many such as structural, storage or even signalling. (Tymoczko et al, 2012 p. 131) Monosaccharides Monosaccharides come in 2 forms, aldoses and ketoses. There can be up to seven carbons in the chain however most monosaccharides contain six called hexoses. Monosaccharides experience optical isomerization and for monosaccharides they are either in a D form or an L form. Most that occur in nature are found in their D form. Monosaccharides can have more than one asymmetric carbon so they can have diastereoisomers. Such as D-glucose, it contains three chiral carbons so it has 2 epimers, D-mannose an epimer at C-2 and D-galactose an epimer at C-4. (Nelson, et al, 2003, p. 294-297) Monosaccharides exist in cyclic form when in solution, this is because the aldehyde group reacts with the alcohol group on the same monosaccharide to form a hemiacetal. Ketoses have the same reaction but with their ketone group to form hemiketals. They can be either pyranoses which are 6 membered cyclics or furanoses, 5 membered cyclics. (Tymoczko et al, 2012 p. 133-134) The creation of these rings forms a new asymmetric carbon called the anomeric carbon. This anomeric carbon forms 2 anomers, alpha and beta. Beta is on top of the anomeric carbon, alpha is below. Alpha and beta anomers have mutarotation, where alpha and beta change into each other through equilibrium. The equilibrium mixture being unique to each monosaccharide. (Nelson, et al, 2003, p. 299) Monosaccharides... ... middle of paper ... ...M. A., Yao, W., Decicco, C., Tortorella, M. D., Liu, R., Copeland, R. A., Magolda, R., Newton, R. C., Trzaskos, J. M. and Arner, E. C. (2003) 'Aggrecan Protects Cartilage Collagen from Proteolytic Cleavage'. Journal of Biological Chemistry, November 14, 278 (46), pp. 45539-45545 DOI 10.1074/jbc.M303737200. Nelson, D. L. Cox, M. M. (2003) Lehninger Principles of Biochemistry, 3rd edition, Worth publishers, New York. Tymoczko, J. L. Jeremy, M. B. Stryer, L. (2011) Biochemistry a short course, 2nd edition, W.H. Freeman and Company, New York. Murray, R. K. Granner, D. K. Mayes, P. A. Rodwell, V. W. (2003) Harpers Illustrated Biochemistry, Lange Medical Books/McGraw-Hill Medical Publishing Division Rajic, A (2013) 'carbohydrates: structure and function' [PowerPoint presentation]. IMDBIS 105 Bioscience Available at: https://learn.ucs.ac.uk (Accessed: 24 November 2013)
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