CARBOHYDRATES

• FUNCTION OF CARBOHYDRATES

  • Structural
  • Energy storage
  • Transport
  • Regulatory
  • Catalytic
  • Filtration barriers
  • Cell differentiation
  • Antigen-antibody interaction
  • Cell lubrication & supportive function
  • Components of cellular membranes
  • Components of clotting proteins
  • Components of protective cellular coats
• CARBOHYDRATES

  • Most abundant biological molecules
  • Composed of C, O, H according to the formula (C•H2O)n where n ≥ 3 
  • Polyhydroxy aldehyde or polyhydroxy ketone
  • Basic carbohydrate unit  = monosaccharides
  • Polymers of monosaccharides units = polysaccharides
• CLASSIFICATION

  Monosaccharide, Disaccharide, Oligosaccharide, Polysaccharide
• MONOSACCHARIDE


  smallest and the building block

  contains only one unit of polyhydroxy aldehyde or polyhydroxy ketone

  they are soluble in water
• DISACCHARIDE


  two monosaccharides bonded by glycosidic bond, also soluble in water
• OLIGOSACCHARIDE


  three to ten monosaccharides, commonly found in conjugated biomolecules
• POLYSACCHARIDE


  hundreds to 50,000 units
• FISCHER PROJECTION


  a two-dimensional representation for showing the configuration of tetrahedral stereocenters
• FISCHER PROJECTION


  horizontal lines represent bonds projecting from the plane of the paper toward the viewer, and vertical lines represent bonds projecting away from the viewer
• STEREOISOMERISM OF MONOSACCHARIDES


  D-monosaccharide,L-monosaccharide
• D-monosaccharidea monosaccharide that, when written as a Fischer projection, has the -OH on its penultimate carbon on the right
• L-monosaccharide 


  a monosaccharide that, when written as a Fischer projection, has the -OH on its penultimate carbon on the left 
• ENANTIOMERS 


  stereoisomers that are mirror images, E.g. D-glucose and L-glucose
• Diastereomers


  stereoisomers that are not mirror images, E.g. D-ribose and D-xylose
• Epimers 


  diastereomers that differ around 1 carbon, E.g. D-glucose and D-galactose
• CYCLIC CARBOHYDRATES


  sugars that contain 4 or more c atoms exist primarily in CYCLIC FORMS
• CYCLIC CARBOHYDRATES


  Ring formation occurs in aqueous solution because aldehydes and ketone groups react reversibly with hydroxyl groups present in the sugar to form cyclic hemiacetals(aldehyde) and hemiketals (ketone)
• CYCLIC CARBOHYDRATES


  Monosaccharides have -OH and C=O groups in the same molecule and exist almost entirely as five- and six-membered rings
• anomeric carbon


  the new stereocenter resulting from cyclic formation
• anomers


  carbohydrates that differ in configuration only at their anomeric carbons
• mutarotation


  The two anomers can freely interconvert in solution
• MUTAROTATION


  The alpha(α) - & beta(β) – forms of monosaccharides are readily interconverted when dissolved in water and produces an equilibrium mixture of α and β forms in both furanose and pyranose ring structures
• HAWORTH PROJECTIONS


  Common way of writing a structural formula to represent the cyclic structure of monosaccharides with a simple three-dimensional perspective
• Five- and six-membered 


  hemiacetals are represented as planar pentagons or hexagons
• COMMON MONOSACCHARIDES


  glucose, fructose, galactose
• GLUCOSE

  • Found in large quantities throughout the living world 
  • Primary fuel for living cells
  • Preferred energy source of brain cells & cells that have few or no mitochondria
  • Large amounts generate energy in cells that have limited oxygen supply (eyeball)
  • Its dietary sources include starch & disaccharides, lactose, maltose, and sucrose
• Glucose is also called


  Dextrose (D-glucose) and blood sugar
• FRUCTOSE


  Also called levulose or fruit sugar

  • Found in some vegetables and in honey 
  • The sweetest sugar, twice as sweet as sucrose
  • Sweetening agent in processed food products
  • Large amounts are used in the male reproductive tract (synthesized in the seminal vesicles and then incorporated into semen, the sperm use fructose as an energy source)
• GALACTOSE

  • Necessary to synthesized lactose, glycolipids, certain phospholipids, proteoglycans, and glycoproteins
  • Readily synthesized from glucose-1-phosphate
• REACTIONS OF MONOSACCHARIDES

  ESTERIFICATION,GLYCOSIDIC BOND
• ESTERIFICATION


  The hydroxyl groups of alcohols can react with acids to produce esters
• GLYCOSIDIC BOND

  the bond from the anomeric carbon to the -OR group
• Glycoside


  a carbohydrate in which the -OH of the anomeric carbon is replaced by -OR
• furanosides


  those derived from furanoses
• those derived from pyranoses

  pyranosides
• • react with alcohols to form the corresponding acetal or ketal


  Hemiacetals & hemiketals
• Acetal of glucose


  glucoside
• ketal of fructose


  fructoside
• • Glycoside derived from sugars with 


  five- membered ring = furanosides, six-membered rings = pyranosides
• If an acetal linkage is formed between the hemiacetal hydroxyl group of one monosaccharide and the hydroxyl group of another monosaccharides, the resulting glycoside is called

  disaccharides