carbohydrates

• Carbohydrates


  • Most abundant class of organic compounds in the plant world
  • Account for 75% of dry plant material and are produced by photosynthesis
  • Act as storehouses of chemical energy (glucose, starch, glycogen)
  • Components of supportive structures in plants (cellulose), crustacean shells (chitin), connective tissues in animals (acidic polysaccharides), essential components of nucleic acids (D-ribose and 2-deoxy-D-ribose)
  • Average human diet contains 2/3 of carbohydrates

  
• Carbohydrate


  Hydrate of carbon, derived from the formula Cn(H2O)m

  
• Carbohydrates


  • Glucose (blood sugar): C6H12O6
  • Sucrose (table sugar): C12H22O11

  
• Carbohydrate


  • Polymer of polyhydroxy aldehydes, a polyhydroxy ketones, or a compound that produces such substances upon hydrolysis
  • Also called "saccharide" from the latin word saccharum meaning sweet taste or sugar
• Classifications of Carbohydrates by number of carbons

  • Triose - 3 carbon atoms
  • Tetrose - 4 carbon atoms
  • Pentose - 5 carbon atoms
  • Hexose - 6 carbon atoms

  
• Aldose


  Carbonyl group is at the end of the chain and represents an aldehyde group
• Ketose


  Carbonyl group occurs within the chain and represents a ketone group
• Monosaccharides


  • D-Aldoses
  • D-Ketoses
• Monosaccharide


  Simplest unit of a carbohydrate, contains a single polyhydroxy aldehyde or polyhydroxy ketone unit, cannot be broken down into simpler units by hydrolysis reactions, also called simple sugars (glucose, fructose and galactose)

  
• Disaccharide


  Consists of two monosaccharide units joined together by a glycosidic bond, commonly crystalline and water soluble (sucrose and lactose)

  
• Oligosaccharide


  Contains ~3-10 monosaccharide units covalently bonded to each other, free oligosaccharides are seldom encountered in biochemical systems, associated with proteins and lipids for structural and regulatory functions

  
• Polysaccharide


  Long polymers of monosaccharide units covalently bonded to each other (cellulose, starch, glycogen)
• Reducing Sugar


  A sugar that reduces Ag+ in the Tollen's test or Cu2+ in the Fehling's or Benedict's test, has a free aldehyde group or is in hemiacetal form (all monosaccharides, lactose and maltose)
• Nonreducing Sugar


  No free aldehyde group, negative for Tollen's, Fehling's or Benedict's test (sucrose and all polysaccharides)
• Pyranose


  Forms a pyran ring upon cyclization
• Furanose


  Forms a furan ring upon cyclization
• In all D-monosaccharides, the CH2OH is above the ring
• The -OH represented to the right of the chain in a Fischer projection is shown below the ring in Haworth projections</b>
• The most stable conformation for most sugars is the chair conformation
• Mutarotation


  Interconversion between the alpha and beta anomers of a monosaccharide
• Optical Activity/Asymmetry


  1. sugars are sweet-tasting and found in carbohydrates, L-sugars are tasteless and have specialized roles
• Polarity/Solubility in Water


  Carbohydrates are soluble in water due to hydrogen bonding
• Stereoisomerism


  Chiral compounds exist in left and right handed forms, the four different groups can occupy two unique spatial arrangements
• Chiral Center


  An atom in a molecule that has four different groups bonded to it
• Optically Active Molecules


  • 2-chlorobutane
  • 2-methylbutanoic acid
  • 2-butanol
  • 1-chloro-3-methylpentane

  
• Not Optically Active Molecules

  • 2-propanol
  • 1-chlorobutane
  • 3-methylhexane
  • 2-butanone
• Almost all monosaccharides are right handed, while amino acids are always left handed
• Humans can only metabolize the D-isomers of monosaccharides, while most animals can only utilize the L-isomers of amino acids to synthesize proteins
• 1. Carvone


  Isomer of D-Carvone
• Enantiomers


  Stereoisomers whose molecules are nonsuperimposable mirror images of each other (D and L)
• Enantiomers


  • Attached atoms or groups on the right in one enantiomer appear on the left side of the other
  • In some instances, only the D or L enantiomers are found in nature
  • If both D and L forms are found in nature, they are rarely found together in the same biological system
• Carbohydrates and amino acids are chiral
• Humans can only metabolize the D-isomers of monosaccharides
• Most animals are only able to utilize the L-isomers of amino acids to synthesize proteins
• Diastereomers


  Stereoisomers that are not exact mirror images
• Epimers


  Diastereomers whose molecules differ only in the configuration at one chiral center
• 1. Glyceraldehyde and Dihydroxyacetone


  Simplest of the monosaccharides, important intermediates in the process of glycolysis

  
• 1. Glucose


  Most abundant in nature, most important source of human nutrition, found in grape fruit and ripe fruits (20–30% by mass), also called Dextrose and Blood sugar (70–100 mg/dL), Diabetics have difficulty getting glucose from the bloodstream into their cells so that glycolysis can occur
• 1. Galactose


  Combined with glucose in the disaccharide lactose, which is present in milk and other dairy products, synthesized in human beings, also called brain sugar, part of brain and nerve tissue, used to differentiate between blood types, six-membered cyclic form

  
• 1. Fructose


  The ketose fructose is also referred to as fruit sugar or levulose, fructose is the sweetest monosaccharide, one and a half times sweeter than table sugar