Chapter 24 Textbook slides

Chapter 24 Textbook slides - CHAPTER 24 CHAPTER 24...

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HAPTER 24 CHAPTER 24 Carbohydrates: Polyfunctional Compounds in Nature
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Names and Structures of Carbohydrates 24-1 ugars are classified as aldoses and ketoses Sugars are classified as aldoses and ketoses. Carbohydrate is the general name for the various forms of sugars (monosaccharides, disaccharides, trisaccharides, polysaccharides). A monosaccharide , or simple sugar , is an aldehyde or ketone ontaining at least two additional hydroxy groups. containing at least two additional hydroxy groups. Aldoses are aldehydic sugars. Ketoses are ketotic sugars. Complex sugars are those formed by the linkage of simple sugars through ether bridges. Based on chain length, sugars are called trioses (C3), tetroses (C4), pentoses (C5) and hexoses (C6).
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Glucose , also known as dextrose, blood sugar or grape sugar is an aldohexose. Glucose is present in many fruits and plants and is present in blood at concentrations of 0.08-0.1%. Fructose is an isomeric ketohexose of glucose. Fructose is the sweetest natural sugar and is present in many fruits and in honey. Ribose is an aldopentose and is a building block of the ribonucleic acids.
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A disaccharide is derived from two monosaccharides by the formation of an ether (usually acetal) bridge. Hydrolysis regenerates the monosaccharides. Trisaccharides, tetrasaccharides and eventually polysaccharides re formed through additional ether bridges are formed through additional ether bridges. Starch and cellulose are two important biological polysaccharides.
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Most sugars are chiral and optically active. With the exception of the ketose, ,3- ihydroxyacetone, most 1,3 dihydroxyacetone, most biological sugars contain at least one stereocenter. The simplest chiral sugar is 2,3-dihydroxypropanal lyceraldehyde) (glyceraldehyde).
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The older D-L convention for naming sugars is still in general use. In this convention, monosaccharides whose highest numbered stereocenter has the same absolute configuration as that of D- (+)-2,3-dihydroxypropanal (D-glyceraldehyde) are labeled D. hose having the opposite absolute configuration are labeled L Those having the opposite absolute configuration are labeled L. Two diastereomers that differ only at one stereocenter are called epimers .
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The D,L nomenclature divides sugars into two groups. For a pentahydroxyhexanal there are 16 stereoisomers divided into two groups: 8 stereoisomers labeled D, and their 8 enantiomers labeled L. Systematic nomenclature of sugar molecules leads to long complex names. As a result, the common names of most sugars are usually used, for example: erythrose and threose for the four aldotetroses.
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Note that the D (or R) label does not necessarily imply (+) and L r S) does not necessarily imply (- (or S) does not necessarily imply ( ). D-glyceraldehyde is detrorotatory. D-erythrose is levorotatory.
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Chapter 24 Textbook slides - CHAPTER 24 CHAPTER 24...

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