Lecture 10-13 - Lecture 10/13-Ch 10 Glucose and sugars pentoses and hexoses can convert to stable ring structures via reaction of OH groups with

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Lecture 10/13-Ch. 10 Glucose and sugars pentoses and hexoses can convert to stable ring structures via reaction of OH groups with the aldehyde (hemiacetal) or ketone (hemiketal) groups in the same molecule hexoses can form either 5 membered rings (furanose)-OR 6 membered rings (pyranose) l 5 member rings are nearly planar; 6 member rings are in the chair conformation o ring structure creates a new chiral carbon--anomeric carbon the anomeric carbon is the most oxidized, it is attached to two oxygen atoms The anomeric carbon has two possible diastereomers called anomers M alpha --OH is down in Haworth projection ! beta --OH is up in Haworth projection l interconversion of alpha and beta forms occurs via the open chain intermediate in solution there is a constant open/closing and changing between alpha and beta forms M enzymes can distinguish between anomers! hexoses can exist in both pyranose and furanose forms in general hexoses prefer to be in the pyranose; exception to rule is fructose in sucrose two conformational isomers for the pyranose ring-"chair and boat" chair form more stable, less steric hindrance from attached groups Important Monosaccharides that you need to recognize the structures of (see handout in Bb!! You need to know only the ring forms (if they are possible) of these simple sugars: o D-glyceraldehyde; dihydroxyacetone o D-ribose (ring); 2-deoxy-D-ribose (ring) o glucose (ring)--primary fuel for cells o fructose (ring)--fruit sugar and honey ketose sugar, sweeter that sucrose on per gram basis o galactose(ring)-component of lactose (milk sugar) precursor of glycolipids, some phospholipids, proteoglycan and glycoproteins do not need a dietary source of galactose, synthesized from glucose-1- phosphate by cell
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Dissacharides-two sugar residues linked in glycosidic bond --Closer Look 10-A energy storage-sucrose, lactose, maltose intermediates in breakdown of polysaccharides-maltose and cellobiose dissacharides are broken down during digestion by enzymes some metabolic diseases are a result of a lack of the enzyme o lactose intolerance is a common example, lack of lactase to cleave lactose into its constituent sugars o galactosemia, enzyme for its metabolism is missing causes liver damage, cataracts and mental retardation due to build up of intermediates monomers may be different or the same linkage involves at least one anomeric hydroxyl configuration of the anomeric carbon at the linkage determines the type of linkage-alpha (OH down) or beta (OH up)
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Reducing Sugars monosaccharides and most disaccharides are reactive at the anomeric carbon readily oxidized--reducing sugars o sugars can be detected by ability to reduce metal ions (Cu or Ag) to insoluble products this property give polysaccharides directionality--a reducing and non-reducing end--this is very important as we will find in metabolism of storage polysaccharides Homopolymers of glucose glycogen--energy reservoir animal, alpha (1-->4)
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This note was uploaded on 12/31/2010 for the course CH 369 taught by Professor Kbrowning during the Spring '07 term at University of Texas at Austin.

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Lecture 10-13 - Lecture 10/13-Ch 10 Glucose and sugars pentoses and hexoses can convert to stable ring structures via reaction of OH groups with

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