Chapter08Fall 2005 - Chapter 8 Carbohydrates Also called...

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Chapter 8 - Carbohydrates Also called saccharides; most abundant molecules on earth. Most are produced by photosynthesis. Uses:  Yield energy (ATP) to drive metabolic processes. Energy-storage molecules (i.e. glycogen, starch). Structural - cell walls and exoskeletons of some organisms. Carbohydrate derivatives found in coenzymes (FAD) and nucleic acids. Can be described by the number of monomers they contain: 1)  monosaccharides  - (CH 2 O)n where n = 3-6; one sugar molecule 2)  oligosaccharides  - polymers from 2-20 3)  polysaccharides  - polymers of greater than 20 sugar residues 4)  glycoconjugates  - derivatives; attached to proteins, lipids, peptide chains Monosaccharides Also known as polyhydroxy aldehydes or ketones. Classified based upon type of carbonyl group (-C-) and number of carbon atoms aldose  - sugar with aldehyde group ketose  - sugar with ketone group There are two important trioses: glyceraldehyde (aldotriose) and dihydroxyacetone (ketotriose) Can have stereoisomers, but the D-form predominates. Naming of sugars: xylose aldose xyulose ketose  add “ul” before “ose”. Both aldoses and ketoses engage in intramolecular cyclization Alcohol + aldehyde =  hemiacetal Alcohol + ketone   =  hemiketal Both 5 and 6 carbon monosaccharides can form hemiacetals. 5-membered =  furanose 6-membered =  pyranose Most oxidized carbon (C-1; attached to 2 oxygen atoms) is known as an  anomeric  carbon. Can adopt either of two configurations. α  - OH group down β  - OH group up Aldoses and ketoses equilibrate between cyclic and open forms. Ring structures can adopt different conformations 5-member - twist (2 carbons approximately coplanar) envelope (4 carbons approximately coplanar) 6-member - chair (more stable due to lack of steric hindrance from 6’ carbon) boat  1
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Derivatives of monosaccharides: 1) Sugar phosphates Metabolized as phosphate esters 2) Deoxy sugars Hydrogen atoms replaces -OH group on C-2. Important to structure of nucleic acids.
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Chapter08Fall 2005 - Chapter 8 Carbohydrates Also called...

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