Carbohydrates: Monosaccharides, Disaccharides, and Polysaccharides

Monosaccharides

  • Simplest carbohydrates.
  • Monomers used to build more complex carbohydrates.
  • Most common:
    • Glucose
    • Fructose

Disaccharides

  • Formed by combining two monosaccharides.
  • Example: Table sugar (sucrose) = glucose + fructose.

Polysaccharides

  • Formed by combining chains of many monosaccharides.

Simple Sugars

  • Names typically end in "-ose."
  • Examples:
    • Glucose
    • Fructose
  • Basic roles:
    • Fuel to do work.
    • Raw materials for carbon backbones.
    • Monomers for synthesizing larger carbohydrates.
  • Sources:
    • Fruits
    • Some vegetables are natural sources of fructose and glucose.

Carbohydrate Solubility

  • Sugars have many polar hydroxyl (OH) groups in their structure.
  • Makes them soluble in water.

Drawing Organic Molecules

  • Organic molecules are three-dimensional and complex.
  • Methods to draw them:
    • Straight line
    • Skeletal (line-angle)
    • Haworth Projections

Straight Line Diagrams

  • Shows all atoms and bonds in the molecule.
  • Does not describe the 3D configuration.
  • Single bonds: 1 line
  • Double bonds: 2 lines
  • Triple bonds: 3 lines

Skeletal Diagram of Glucose (line-angle)

  • A carbon atom is assumed to be at each vertex of the central figure.
  • Single bonds are single lines, double bonds are double lines, and triple bonds are triple lines.
  • When there are less than four bonds at a vertex, there are assumed to be enough H atoms to form 4 bonds with the C there.
  • Wedge lines show a bond coming out of the page.
  • Dashed lines show a bond going into the page.
  • Wavy lines indicate atoms present that are omitted from the diagram.

Haworth Projection of Glucose

  • The numbers represent the carbon atoms.
  • H atoms are not indicated, but are understood to be attached to the C atoms when there are not 4 bonds shown.
  • The thicker lines provide perspective by showing that the atoms are closer to the viewer.

Carbohydrate Structures

  • In solution, sugars form cyclic structures that can connect to form chains of sugars.
  • Examples:
    • Fructose
    • Glucose
    • Sucrose

Disaccharides

  • Cells link 2 simple sugars together to form disaccharides.
  • Disaccharide formation is another example of a dehydration synthesis reaction.
  • The most common disaccharide is sucrose (fructose + glucose).
  • Example: Sucrose