4 Ijesha Close, Ilupeju, Lagos
+2347 086 296 002

Biological Molecules

  • All living things are made up of four classes of large biological molecules:
    • Carbohydrates,
    • Lipids,
    • Proteins, and
    • Nucleic acids
  • These are sugars made up of the elements carbon, hydrogen, and oxygen
  • They can be simple, soluble or complex sugars.


  • They are the simplest carbohydrate monomers.
  • Glucose (C6H12O6), fructose, and ribose are examples of monosaccharides.


  • Two monosaccharides bond together using a dehydration reaction. E.g. Sucrose, Maltose, Lactose.


  • Many monosaccharides linked together through glycosidic bonds. There are two types of polysaccahrides:
    • Storage Polysaccharides: Glycogen found in animals, starch found in plants
    • Structural Polysaccharides: Cellulose, chitin
  • They are made up of carbon, hydrogen, oxygen.
  • Examples are oils, fats, phospholipids, steroids.
  • Fats are made up of glycerol and 3 fatty acids. The major function of fats is energy storage
  • They are made up of the elements carbon, hydrogen, oxygen, and nitrogen
  • They are made up of 20 different amino acids. A small protein molecules might be made up from a chain consisting of a hundred or so amino acids.

Types of Proteins

  • Structural proteins
  • Enzymes: The activity of an enzyme depends on the shape as it creates an active site, which has a complementary shape to the substrate molecule on which it acts.
  • Antibodies: Antibodies are produces by specialized white blood cells called B lymphocytes. The primary function of an antibody is to bind foreign molecules called¬†antigen with complementary shapes facilitating their destruction.

Structure of DNA

  • A DNA molecule is made up of long chains of nucleotides, formed into two strands. The double strand is twisted to form a helix
  • A nucleotide is a 5-carbon sugar molecule joined to a phosphate group (-PO3) and an organic base.
  • In DNA, the sugar is deoxyribose and the organic base is either adenine (A), thymine (T), cytosine (C) or guanine (G)
  • The nucleotides are joined by their phosphate groups to form a long chain, often thousands of nucleotides long.
  • A (adenine) always pairs with T (thymine), and C (cytosine) pairs with G (guanine)
  • Water is important as a solvent.
  • The role of water as a solvent in organisms:
    • It acts as a transport medium in plants.¬†Water passes up the plant from the roots to the leaves in xylem vessels and carries with it dissolved mineral ions. Phloem vessels transport sugars and amino acids in solution from the leaves to their places of use or storage.
    • It acts as a powerful solvent for excretory materials, such as nitrogenous molecules like urea, as well as salts, spent hormones and drugs. Water has a diluting effect, reducing the toxicity of the excretory materials.
Food Test
  1. Test for Starch:
    • Shake a little starch powder in a test-tube with some warm water to make a suspension.
    • Add 3 or 4 drops of iodine solution.
    • A dark blue color should be produced
  2. Test for Reducing Sugar:
    • Heat a little glucose solution with an equal volume of Benedict’s solution in a test-tube.
    • The heating is done by placing the test-tube in a beaker of boiling water, or warming it gently over a blue Bunsen flame.
    • However, if this second technique is used, the test-tube should be moved constantly in and out of the Bunsen flame to prevent the liquid boiling and shooting out of the tube.
    • The solution will change from clear blue to cloudy green, then yellow, and finally to a red precipitate (deposit) of copper (I) oxide
  3. Test for Protein (Biuret Test):
    • To a 1% solution of albumin (the protein of egg-white) add 5 cm3 dilute sodium hydroxide (this solution is caustic), followed by 5 cm3 1% copper sulfate solution.
    • A purple color indicates protein.
    • If the copper sulfate is run into the food solution without mixing, a violet halo appears where the two liquids come into contact.
  4. Test for Fat:
    • Shake two drops of cooking oil with about 5 cm3 ethanol in a dry test-tube until the fat dissolves.
    • Pour this solution into a test-tube containing a few cm3 of water.
    • A milky white emulsion will form. This shows that the solution contained some fat or oil.
  5. Test for Vitamin C:
    • Draw up 2 cm3 of a 0.1% solution of DCPIP (a blue dye) in a test-tube.
    • The DCPIP will become colorless quite suddenly as the juice is added.
    • The amount of juice added from the syringe should be noted down
    • Repeat the experiment but with orange juice in the syringe
    • If it takes more orange juice than lemon juice to decolorize the DCPIP, the orange juice must contain fewer vitamins.
Minimum 4 characters