carbohydrates

• Chirality


  Handedness in molecules
• Glycolipids and glycoproteins


  Cell recognition
• Carbohydrates account for 75% of dry plant material and are produced by photosynthesis
• Photosynthesisformula

  CO2 + H2O + solar energy → carbohydrates + O2
• Functions of Carbohydrates in the Human Body

  • Provide energy
  • Supply carbon atoms for synthesis of other biochemical substances
  • Structural components of cell membranes
  • Cell-cell and cell-molecule recognition processes
• Empirical formula of simple carbohydrates

  CnH2nOn or Cn(H2O)n (hydrate of C)
• Carbohydrate


  Polyhydroxy aldehyde, ketone, or a compound that produces such substances upon hydrolysis
• Monosaccharides


  Contain single polyhydroxy aldehyde or ketone unit, cannot be broken down into simpler substances by hydrolysis reactions, contain 3–7 C atoms, 5 and 6 carbon species are more common, pure monosaccharides are water soluble white, crystalline solids
• Disaccharides


  Contain 2 monosaccharide units covalently bonded to each other, crystalline and water soluble substances, upon hydrolysis they produce 2 monosaccharide units
• Oligosaccharides


  Contain three to ten monosaccharide units covalently bonded to each other, usually found associated with proteins and lipids in complex molecules, serve structural and regulatory functions
• Polysaccharides


  Contain many monosaccharide units covalently bonded, number of monosaccharide units varies from a few 100 units to 50,000 units
• Polysaccharides

  • Cellulose - Paper, cotton, wood
  • Starch - Bread, pasta, potatoes, rice, corn, beans, and peas
• Chirality


  Handedness in molecules, most biological molecules exhibit this property
• Mirror images


  Reflection of an object in a mirror, can be superimposable or nonsuperimposable
• Chiral center


  C atom attached to 4 different groups, a molecule with a chiral center is said to be chiral
• D isomer of a carbohydrate


  The -OH group on the chiral carbon farthest from the carbonyl group is pointing to the right
• Stereoisomers


  Isomers that have the same molecular and structural formulas but differ in the orientation of atoms in space
• Enantiomers


  Stereoisomers whose molecules are non-superimposable mirror images of each other
• Diastereomers


  Stereoisomers whose molecules are not mirror images of each other
• Constitutional isomers differ in most chemical and physical properties
• Properties of enantiomers

  • interaction with plane polarized light
  • interaction with other chiral substances
• Dextrorotary and Levorotatory compounds

  Enantiomers are optically active, dextrorotatory compounds rotate light towards right, levorotatory compounds rotate light towards left
• Diastereomers


  Compounds that are not mirror images of each other
• Enantiomers


  Compounds that are mirror images of each other
• Nearly all the properties of a pair of enantiomers are the same, except for two differences: their interaction with plane polarized light and their interaction with other chiral substances
• Dextrorotatory compound


  Chiral compound that rotates light towards right (clockwise; +)
• Levorotatory compound


  Chiral compound that rotates light towards left (counterclockwise; -)
• Enantiomers have same boiling points, melting points, and densities as these are dependent upon intermolecular forces, whereas chirality doesn't depend on such forces
• Classification of monosaccharides based on number of carbon atoms

  • Triose - 3 carbon atoms
  • Tetrose - 4 carbon atoms
  • Pentoses - 5 carbon atoms
  • Hexoses - 6 carbon atoms
• Classification of monosaccharides based on functional groups

  • Aldoses: Monosaccharides with one aldehyde group
  • Ketoses: Monosaccharides with one ketone group
• Aldohexose


  Monosaccharide with aldehyde group and 6 C atoms
• Ketopentose


  Monosaccharide with ketone group and 5 C atoms
• 1. Glucose


  Most abundant in nature, most important source of human nutrition, grape fruit and ripe fruits are good sources, also named grape sugar or blood sugar
• 1. Galactose


  Milk sugar, synthesized in human beings, also called brain sugar, used to differentiate between blood types
• 1. Fructose


  Ketohexose, sweetest tasting of all sugars, found in many fruits and in honey, good dietary sugar due to higher sweetness
• 1. Ribose


  Part of a variety of complex molecules which include RNA, ATP, and DNA
• α-D-Glucose


  Cyclic form of D-Glucose where the -OH of C1 and CH2OH of C5 are on opposite sides
• β-D-Glucose


  Cyclic form of D-Glucose where the -OH of C1 and CH2OH of C5 are on the same side
• Anomers


  Cyclic monosaccharides that differ only in the position of the substituents on the anomeric carbon atom
• Pyranose


  Cyclic monosaccharide containing a six-atom ring