Chemical composition of protein

Proteins such as enzymes carry out work in a cell. Protein can also provide structures such as gates, channels, support rods that give the cell its shape. So what are proteins, such as enzymes, made of?

Time for some heat! Gently heat a small quantity of gelatine crystals (protein) in a test tube, while holding a piece of moist red litmus paper at its mouth.

Consider these questions:

  1. Does water condense on the sides of the test tube?
  2. Does the gelatine decompose leaving a black residue?
  3. Does litmus paper turn blue?
  4. What gas produces this change in litmus?
  5. What elements do these results suggest are present in gelatine?
  6. When heated strongly, gelatine gives off an odour. What does the odour remind you of?

You can repeat this experiment with hair or other protein such as egg.


1) Water condenses on the glass surface. If heating is too fierce at first the beads of water will be masked by tar and tarry vapours.
2) The black residue is Carbon.
3 and 4. Moist red litmus turns blue indicating the presence of ammonia
5) This suggests that C, H, O, N are present in the gelatine protein
6) The smell is like burning leather. This odour is characteristic of proteins when decomposed by heat.


  1. Proteins often fold up into specific shapes. What is meant by the terms primary, secondary and tertiary structure?
  2. How does heat affect the way a protein folds? What are the consequences for the cell?
  3. How does the cell know what proteins to make? What is the significance of the genetic code and the process of translation?
  4. How is genetic engineering connected to question 3 above?
  5. The interactive pages...identify these pieces of lab equipment
  6. The interactive pages...weird metals and gases hide in this Periodic Table

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