Science & Technology in Action

3rd Edition

Experiments with Enzymes


This lesson describes six experiments that demonstrate the effects of temperature, concentration etc. on the action of catalase, an enzyme that decomposes hydrogen peroxide.
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Lesson excerpt

At Junior Certificate level you carried out two experiments using catalysts – (a) the production of oxygen gas from hydrogen peroxide using the inorganic black powder, manganese dioxide, as the catalyst and (b) the breakdown of starch to maltose sugar using amylase as the organic orbiological catalyst.

A catalyst is a substance that alters the rate of a chemical reaction without being used up in that reaction. A biologicalcatalyst is known as an enzyme. Substances that slow down the rate of a reaction are known as inhibitors or negative catalysts. Enzymes are positive catalysts speeding up reactions by as much as a hundred million million times. They are very selective; they typically affect only one specific reaction; for example, -amylase breaks starch into glucose subunits.

Enzymes are essential for life and an understanding of how they operate is important for medicine and industrial biochemistry.

How enzymes operate – the active site theory of enzyme action

  1. The active site of the enzyme has a shape closely complementary to the substrate.
  2. The substrate locks into the enzyme’s active site.
  3. The shape of the active site changes slightly gripping the substrate more tightly and straining it; an enzyme-substrate complex is formed.
  4. The substrate undergoes a chemical change – the new substance (the product) is released from the active site.  The active site springs back to its original shape and is ready to receive fresh substrate.

Note: For enzymes to operate they must be able to make contact with the substrate; the enzyme or substrate or both must be in solution, i.e. in rapid random motion in water. Our cells are about 90% water and water is the medium in which most of ourbiochemistry takes place.

Six enzyme practicals using catalase to decompose hydrogen peroxide

2H2O2                 2H2O  +  O2

Catalase is present in the cells of fungi, plants and animals. Hydrogen peroxide is poisonous and is a dangerous waste product of many different biochemical reactions that occur in ourcells. Our cells produce the enzyme catalase which decomposes hydrogen peroxide to water and oxygen. Catalase operates very quickly – one molecule of catalase can break down 40 million hydrogen peroxide molecules a second. 


True or False?

  1. An enzyme is a positive biological catalyst true
  2. Enzymes slow down the rate of biochemical reactions. false
  3. Each particular type of biochemical reaction has its own enzyme. true
  4. Catalase speeds up the decomposition of hydrogen peroxide true
  5. The rate of enzyme action is not affected by temperature. false
  6. pH is kept constant by use of a buffer. true
  7. Catalase operates best at pH 2 false
  8. Enzyme action decreases with increase of enzyme concentration false
  9. Catalase operates fastest at approx 40°C. true
  10. Excessive temperature destroys the catalytic ability of enzymes. true