Carb

• Learning Outcomes


  • Use chemical tests to identify physical and chemical characteristics of typical carbohydrates
  • Differentiate between monosaccharides, disaccharides, and polysaccharides
  • Identify an unknown carbohydrate
• Functions of Carbohydrates


  • Provide energy through oxidation
  • Glycogen provides short-term energy reserve
  • Supply carbon atoms for synthesis of other biochemical substances
  • Form part of structural framework of DNA & RNA
  • Play key roles in cell-cell recognition processes
• Classification of Carbohydrates


  • Monosaccharides (aldoses, ketoses)
  • Disaccharides (can be hydrolyzed to two monosaccharides)
  • Polysaccharides (hydrolyze to many monosaccharide units, e.g. starch, cellulose)
• Monosaccharides


  • Classified by: aldose or ketose, number of carbons in chain
• Monosaccharides


  • Glucose (D-aldohexose)
  • Fructose (D-ketohexose)
• Haworth Projection


  Method to depict ring structures (flat), with O in the back, OH to the right down, OH to the left up, D-sugars have last CH2OH group up
• Pyranose


  Sugars with six-membered rings
• Furanose


  Sugars with five-membered rings
• Converting Fischer to Haworth Projections

  Draw the ring with O in the back-right, arrange OH groups up/down accordingly
• Converting Haworth to Chair Conformation

  Draw the Haworth projection, draw the chair skeleton with O upper rear-right, add substituents, verify largest groups in equatorial positions
• Disaccharide


  Formed by dehydration reaction joining two monosaccharides, covalent bond is a glycosidic linkage
• Disaccharides


  • Maltose (two glucose units 1-4')
  • Sucrose (glucose + fructose 1-2')
  • Lactose (glucose + galactose 1-4')
• Reducing Sugars


  Sugars with free anomeric carbon or hemiacetal, can be oxidized to aldonic acid
• All monosaccharides are reducing sugars
• Identifying Reducing Sugars


  Locate anomeric carbon, check if attached group is OH
• Nonreducing Sugars


  Glycosides, disaccharides, polysaccharides are acetals, stable in base
• Polysaccharides


  • Starch (amylose, amylopectin)
  • Glycogen
• Hydrolysis


  Cleavage of chemical bonds by addition of water, breaks glycosidic bonds
• Benedict's Test


  Determines presence of reducing sugars, Cu2+ reduced to Cu2O forming orange-red precipitate
• Barfoed's Test


  Distinguishes reducing monosaccharides from disaccharides, monosaccharides react faster
• Seliwanoff's Test


  Distinguishes ketohexoses (rapid deep red) from aldohexoses (slow light pink)
• Iodine Test


  Tests for polysaccharides, forms colored complexes based on chain length and branching
• Fermentation


  Metabolic process where carbohydrates are converted to alcohol and CO2 by yeast
• Yeast can ferment glucose, fructose, maltose and sucrose
• Experiment involves testing carbohydrates using Benedict's, Barfoed's, Seliwanoff's, Iodine tests, and hydrolysis, as well as identifying an unknown carbohydrate