3-423-08-GlycolysisStudent - LECTURE Carbohydrates...

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LECTURE: Carbohydrates; Glycolysis Objectives Understand the difference between the structures of aldoses and ketoses. Be able to draw the structures of glucose and fructose. Know the structures of the disaccharides sucrose and lactose and understand the differences between α♦ and β glycosidic linkages. Understand the overall purpose of glycolysis. Know -the NAMES, STRUCTURES, ENZYMES, COFACTORS of all of the steps of glycolysis -the NET EQUATION of glycolysis -the fates of pyruvate after glycolysis (and when/where they occur) -Know on a basic level how fructose and galactose enter the glycolytic pathway, and from what sources. Re-Introduction of Carbohydrates Carbohydrates = polyhydroxy aldehydes and ketones I. Monosaccharides simplest carbohydrates: aldehydes or ketones with hydroxylated methylene groups - empirical formula (CH 2 O) n n = 3, triose n = 4, tetrose n = 5, pentose n = 6, hexose aldose - aldehyde sugar ketose - ketone sugar The two smallest monosaccharides: glyceraldehyde and dihydroxyacetone Glucose, fructose, most common hexoses: must know structures! Glyceraldehyde has one asymmetric carbon - D or L. If we extend the series, a tetrose has 2 asymmetric carbons, a pentose 3, and a hexose 4 asymmetric carbons. For monosaccharides with more than 1 asymmetric carbon, the absolute configuration, given as a prefix to the name of the compound, refers to the asymmetric carbon that is farthest from the carbonyl.
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If n = no. of assymmetric carbons, the number of stereoisomers is 2 n enantiomers - mirror image steroisomers epimers - steroisomers that differ in configuration about only 1 asymmetric carbon atom. Epimers of glucose include mannose, galactose diastereomers - stereoisomers that are not enantiomers II. Ring Formation In solution, pentoses and hexoses form rings rather than open chains. The aldehyde reacts with an alcohol to form a hemiacetal or a ketone reacts with an alcohol to form a hemiketal. Aldose - C1 aldehyde reacts with C5 OH to form a six member ring called a pyranose ring. Ring formation creates an additional asymmetric carbon at C1 for aldoses and C2 for ketoses. The configuration of this carbon is designated either alpha or beta. Alpha - C1 OH lies “below” the ring Beta - C1 OH lies “above” the ring The C1 or C2 is known as the anomeric carbon, so alpha and beta configurations are anomers. Because the ring forms are in equilibrium with the open chains, free rings can switch their alpha or beta configuration in solutions, a phenomenon called mutarotation. Ketose - C2 carbonyl reacts with C5 OH to form a five member ring called a furanose ring. Fructose : C2 reacts with C5, makes a furanose ring. aldopentoses - form furanose rings ketopentoses - no rings III. Monosaccharide derivatives Phosphorylated sugars - major metabolic intermediates. Sugars act as both acceptors and donors of phosphate groups. Glycolysis - all but first and last steps involve a phosphorylated sugar.
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3-423-08-GlycolysisStudent - LECTURE Carbohydrates...

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