Th03L03 Carbohydrates

Th03L03 Carbohydrates

1. Properties

   • Monosaccharides: sugars
   • Water-soluble
   • General formula: (CH20)n
     • Usually n=3, 4, 5 or 6
       • Triose (n=3) e.g. glyceraldehyde, dihydroxyacetone
       • Pentose (n=5
         • 2-deoxyribose, ribose
       • Hexoses (n=6)
         • Glucose, fructose

2. Structure

   • Carbonyl group (C=0)
     • Located in the middle of the ketose molecule and end of the aldose molecule
   • Carbon 1 = at the end closest to the carbonyl group
   • Anomeric carbon - carbon attached to the original carbonyl group in cyclic form
   • Isomers
     • Aldose and ketone
       • Aldose
         • contains the aldehyde groups (-CH=O)
         • Adloses with three or more carbon isomers exhibit stereoisomerism
           • same molecule that differs in dimensional orientations of their atoms in space affecting properties of the molecule
       • Ketone
         • contains the fructose groups
     • Different molecules with same chemical formula
     • Galactose, mannose and glucose
   • D vs. L form
     • Isomeric forms
     • D-sugar is most common biologically
   • Ring formation
     • In aqueous solution, the aldehyde or ketone group tend to react with a hydroxyl group of the same molecule, closing the molecule into a ring structure
   • Alpha and beta forms
     • Hydroxyl group (-OH) of the carbon that carriers the aldehyde or ketone group can rapidly change from one position to another
     • Alpha form: hydroxyl group is facing up
     • Beta form: hydroxyl group is facing down

3. Biological functions

   • Sugars function in short-term fuel for muscle, brain kidney, etc.
   • Function as energy forces or energy storage in the form of glucose and glycogen respectively
     • Digestion of alpha-amylase results in the random hydrolysis of internal alpha 1>4 linkages in the glycogen molecule
     • Pancreatic alpha-amylase mixture of mono and disaccharides continues hydrolysis of internal linkages
     • Maltase produces glucose and can be absorbed into intestinal mucosal cells
     • In the liver, glucose phosphorylase hydrolyses terminal alpha (1>4) to produce glucose-1- phosphate
   • Structurally part of cell walls in the bacteria (peptidoglycan)
   • Proteins on the cell surface are often glycosylated (e.g. ABO blood groups and IgG)

4. Pathology

   • Lactose intolerance
     • Normally lactose is broken down into galactose and glucose              When lactose remains undigested, it can be digested by bacteria in the large intestine producing excess CO2 and other metabolites > bloating and diarrhoea   

5. Disaccharides

   • Sucrose
     • glucose + fructose
   • Maltose
     • glucose + glucose
   • Galactose
     • glucose + galactose

6. Polysaccharides

   • Glycogen (branched glucose polymer)
     • Stored form
     • Linear glucose polymer (alpha 1>4)
     • Alpha (1>6) branches
   • Amylose (linear glucose polymer)
   • Glycosidic bond formation
     • Gycosyltransferase via a dehydration (condensation) reaction

7. Monosaccharide

   • Reducing form

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