Carbohydrates

• Carbohydrates include sugars and their polymers
• The simplest carbohydrates are monosaccharides, or simple sugars
• Monosaccharides are the monomers from which more complex carbohydrates are built
• Disaccharides are double sugars, consisting of two monosaccharides joined by a covalent bond
• Carbohydrate macromolecules are polymers called polysaccharides, composed of many sugar building blocks
• Monosaccharides generally have molecular formulas that are some multiples of CH2O
• Glucose(C6H12O6) is the most common monosaccharide and of central importance in the chemistry of life
• Glucose contains a carbonyl group (C=O) and multiple hydroxyl groups (OH)
• Monosaccharides are classified by

  –The location of the carbonyl group

  –The number of carbons in the carbon skeleton
• Monosaccharides serve as a major fuel for cells and as raw material for building molecules
• In cellular respiration, cells extract energy from glucose by breaking them down in a series of reactions
• Monosaccharides that aren't immediately used are incorporated as monomers into disaccharides or polysaccharides
• A disaccharide consists of two monosaccharides joined by a glycosidic linkage
• Glycosidic Linkage

  A covalent bond formed between two monosaccharides by a dehydration reaction
• Disaccharides must be broken down into monosaccharides to be used for energy by organisms
• Polysaccharides are macromolecules
• Some polysaccharides serve as storage material, while others serve as building material
• Both plants and animals store sugars for later use in the form of storage polysaccharides
• Starch

  • Used by plants to store glucose in the form of a polymer
  • It can be later restored through hydrolysis which breaks the bonds between glucose monomers
  • The glucose monomers within starch are in alpha configuration
• Glycogen

  • Used by animals to store glucose in the form of a polymer
  • Humans and other vertebrates store glycogen mainly in liver and muscle cells
  • The breakdown of glycogen releases glucose when the need for energy increases.
• Cellulose

  • Like starch, cellulose is a polymer of glucose, however the glucose monomers within cellulose are in beta configuration
  • A structural polysaccharide of plant cell walls
• Chitin

  • A structural polysaccharide consisting of amino sugar monomers
  • Found in many fungal cell walls and in the exoskeletons of arthropods
  • Similar to cellulose, it contains beta linkages except the glucose monomers of chitin have a nitrogen containing attachment