Lecture 15. Carbohydrates
Tuesday 19 March 2019
Simple carbohydrates: monosaccharides. Pentoses and hexoses. Furanose and pyranose rings and their conformations. Complex carbohydrates. Glycobiology.
Reading: Lehninger - Ch.7, pp.241-252.
Summary
Reading summary. §7.1 Monosaccharides and disaccharides. The two families of monosaccharides are aldoses and ketoses. Monosaccharides have asymmetric centers. The common monosaccharides have cyclic structures. [Fischer projections; 3-6 carbon aldose and ketose series, epimers; formation of hemiacetals, hemiketals, acetals and ketals; cyclization, formation of pyranose and furanose rings, anomers, Haworth projections, onosaccharides, "conformational formulas" (chair representation of pyranose ring)] Organisms contain a variety of hexose derivatives. Box 7-1 -Medicine- Blood glucose measurements in the diagnosis and treatment of diabetes. Monosaccharides are reducing agents. Disaccharides contain a glycosidic bond. Box 7-2 Sugar is sweet, and so are...a few other things (pp.252t-253t).
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Carbohydrates are the prime example of metabolic "fuel" for cells. The stepwise degradation of the monosaccharide glucose is a nearly universal pathway that yields biochemical energy in the form of adenosine triphosphate (ATP). Plants, in carrying out photosynthethesis, harvest the energy of sunlight by using it to convert carbon dioxide and water into carbohydrates. Glucose, fructose, and ribose are among the most common monosaccharides in biochemistry, a monosaccharide being a carbohydrate that cannot be broken down into simpler carbohydrate fragments. Polymeric forms of such simple carbohydrates are the complex carbohydrates. Furthermore, carbohydrate moeities are linked to or incorporated in other biomolecules, forming nucleotides, glycolipids, and glycoproteins. Glycobiology examines the roles of carbohydrates, glycoproteins, and other glycoconjugates in cellular and multicellular structure and function.