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...
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...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.
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Carbohydrates are biomolecules that consist of a chain or ring of carbon atoms attached to hydrogen and oxygen atoms. The simplest formula for carbohydrates is (CH2O)n. Carbohydrates are important to organisms for a variety of reasons. They are used to form the structural components of the cell, aid in energy storage, and serve as intermediary compounds for more complex molecules. Carbohydrates are classified as either monosaccharides, disaccharides, or polysaccharides. Both monosaccharides and disaccharides dissolve easily in water. Carbohydrates are produced in plants through the process of photosynthesis and animals obtain these carbohydrates by eating the plants. ("BIO 1510 Laboratory Manual," 2016)
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All monosaccharides are reducing sugars because they all aldehydes. Different monosaccharides contain different number of carbon atoms. There are three types of monosaccharides, trioses, pentose and hexose. They generally contain three (trioses), five (pentoses) or six (hexoses) carbon atoms. Triose is used as a product in biochemical pathways of respiration and photosynthesis.
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During the TCA cycle, pyruvate is oxidized to acetyl CoA, which undergoes a condensation reaction catalyzed by citrate synthase to form citrate. Citrate can then be isomerized to form isocitrate, which undergoes oxidative carboxylation that is catalyzed by isocitrate dehydrogenase, to form α -ketoglutarate. Succinyl CoA is then formed from the decarboxylation/oxidation of α -ketoglutarate, which is catalyzed by α -ketoglutarate dehydrogenase. Succinyl CoA can be used to form products including chlorophyll, heme, and prophyr...
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1. What is the difference between a monosaccharide and a disaccharide? Provide examples of each.
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