Chemical Elements of Biomolecules

• Carbohydrates : Carbon, Hydrogen, Oxygen
• Proteins: Carbon, Hydrogen, Oxygen, Nitrogen, Sulfur
• Carbon, Hydrogen, Oxygen

Tip: You can tell the chemical elements that make up carbohydrates by their name. Carbo = Carbon, hydr = Hydrogen, and ate = Contains oxygen.

Large and Small Molecules

Large molecules are made from smaller molecules:

• Starch, glycogen, and cellulose from glucose
• Proteins from amino acids
• Fats and oils from fatty acids and glycerol

Chemical Tests for Biological Molecules

1. Starch test
   Add 2-3 drops of iodine solution onto the extract/into the test-tube. If starch present (Positive result), colour turns from yellow-brown to blue-black
2. Reducing Sugars test
   Using Benedict’s solution, add it to a test-tube with extract and heat gently in a water bath.
   Original colour – Bright blue
   Traces of reducing sugar – Green/yellow
   Moderate amount of reducing sugar – Orange
   Large amount of reducing sugar – Brick-red
3. Protein test
   Add 5-6 drops of biuret solution to the test-tube with extract.
   Original colour – Blue
   Protein present – Purple
4. Fat test
   Chop or grind testing material, do not add water yet. Place the extract into the test-tube. Add enough ethanol to cover the test-tube. Add a stopper and shake the test-tube. Add distilled water, shake again.
   Original – Clear
   Fat present – Cloudy/milky
5. Vitamin C test
   Add liquid extract to DCPIP solution in test-tube drop one drop at a time.
   Original colour – blue
   Vitamin C present – Colour disappears