Carbohydrate Chemistry Overview

Carbohydrate Chemistry

• Carbohydrates are aldehyde or ketone derivatives of polyhydric alcohols
• Carbohydrates serve as a source of energy (e.g., glucose) and form structural components of animal and plant cells (e.g., cellulose and chitin)
• Carbohydrates can combine with lipids (glycolipids) or proteins (glycoproteins), forming parts of cell membranes and ground substance between tissues

Classification of Carbohydrates

• Classified based on the number of sugar units:
  • Monosaccharides (one sugar unit)
  • Disaccharides (two sugar units)
  • Oligosaccharides (3-10 sugar units)
  • Polysaccharides (more than 10 sugar units)
• Monosaccharides are further classified by:
  • Number of carbon atoms (triose, tetrose, pentose, hexose, heptoses)
    • Triose: 3 carbon atoms
    • Tetrose: 4 carbon atoms
    • Pentose: 5 carbon atoms
    • Hexose: 6 carbon atoms
    • Heptose: 7 carbon atoms
  • Functional group (aldose or ketose)
    • Aldoses: contain an aldehyde group
    • Ketoses: contain a ketone group

Important Sugars (Examples)

• Table of important aldoses and ketoses, including their chemical formulas: (This table is found in image pages 7,8,9,10,11)
  • Aldotriose: glycerose, dihydroxyacetone
  • Aldotetrose: erythrose, erythrulose
  • Aldopentose: ribose, ribulose, lyxose, xylose, arabinose-D-ribose
  • Aldohexose: glucose, fructose, galactose, mannose
• Examples of specific monosaccharides' structures are shown. (image pages 8,9,10)

Monosaccharides: Nomenclature

• The suffix "-ose" indicates a sugar
• Aldoses contain an aldehyde group
• Ketoses contain a ketone group

Isomers

• Isomers are compounds having the same molecular formula but different spatial configuration
• Asymmetric carbon atoms (attached to 4 different groups/atoms):
  • Any substance containing one asymmetric carbon atom has two isomers
  • A substance with 2 or more asymmetric carbon atoms can exist in 2ⁿ isomers, where 'n' is the number of asymmetric carbon atoms

Enantiomers

• Monosaccharides are classified into D and L forms based on the position of hydroxyl (-OH) groups on carbon atoms adjacent to the last CH₂OH. Most monosaccharides in mammals are of the D-configuration
• Examples of isomers are shown. (Image page 20)

Pyranose and Furanose Forms

• Stable ring structures of monosaccharides are pyranose (six-membered ring) or furanose (five-membered ring)
• Most glucose exists in pyranose form. (Image page 21,22)

Anomers

• Anomers are isomers obtained from the change of position of hydroxyl group attached to the anomeric carbon. (Image page 23,24)
• Anomeric carbon: the carbon atom obtained from the active carbonyl sugar group.
  • Carbon number 1 in aldoses
  • Carbon number 2 in ketoses

Physical Properties

• All monosaccharides are soluble in water
• All monosaccharides exhibit optical activity