Learning objectives

    • define an enzyme
    • explain the properties of enzymes
    • explain enzyme action
    • investigate factors that affect the rate of enzyme catalyzed reactions
  • enzymes are proteins that act as biological catalysts
  • catalyst is a molecule that speeds up a chemical reaction, but it remains chemically unchanged


Examples of enzymes
  • pepsin,
  • salivary amylase,
  • trypsin etc


Enzyme Specifity

  • they are specific
  • this can be demonstrated by the lock and key hypothesis
  • specific shape can fit into a complementary key



  • all reaction needed in order stay alive
  • can be catabolic reactions, breaking down reactions.
  • or can anabolic reaction ie build up reactions


Characteristics Of Enzymes

  • they are proteins
  • they alter or speed up the rates of chemical reactions they catalyze
  • they remain unchanged after the chemical reaction
  • they are specific- catalyze only one type of reaction eg amylose act on starch to produce sugar
  • they are affected by temperature, pH etc


Factors Affecting Enzyme Activity



  • The enzyme activity is increasing as the temperature increases as the molecules gain k energy.
  • The enzyme works best at its optimal temperature
  • The enzyme activity decreases at temperature above the optimal temperature, at extreme temperature, the enzyme stopped as they are denatured



  • The enzyme activity is increases from its inactive state as the pH (acidity/alkalinity) increases
  • The enzyme is at its most active state at optimum/optimal pH (optimum acidity/optimum alkalinity)
  • Most enzymes work best at neutral pH, some enzymes work best at acidic pH and some enzymes work best at alkaline pH
  • eg pepsin is found in the stamach which is acidic and trypsin si found in the duodenum where the medium is alkaline
  • The enzyme activity decreases
  • when it is exposed to above the optimal pH, the enzyme stopped because they are denatured.


Enzyme Inhibitor

• An enzyme inhibitor is a substance that binds to the enzyme and decreases its activity.
• The presence of these inhibitors decreases the enzyme activity and so the rate of reaction.
• There are two types of inhibitors


1. competitive inhibitor

• Competitive inhibitors are inhibitors that bind at the enzyme’s active site.
• They compete with substrates for the active site.


2. Non-competitive inhibitor

• Non-competitive inhibitors are inhibitors that bind at a site other than the enzyme’s active site.
• When they bind to the enzyme the shape of the active site is changed.


Industrial application of enzymes

1. Biological washing powder

  •  Biological washing powder contains many enzymes such as lipase and protease which remove
    fats, grease and protein stains from the fabrics.
  • When the washing powder is soaked in water with fabrics, enzymes break down stains into
    soluble molecules which can be washed away easily.
  • This is why biological washing powders are effective at removing hard stains like grease or
    bloodstains from fabrics.

2. Beer formation

  • Beer is formed by fermenting sugar using yeast.
  • Amylase, an enzyme, is used to break down starch into simpler sugars that can be usable by

3. Cheese making

  •  Enzymes play an essential role in cheese making.
  •  Rennet enzyme is used.
  • This enzyme contains rennin and pepsin that coagulate milk to curd.


4. Baking

  • Amylase is used in the baking industry.
  •  This enzyme breaks down starch into simpler sugars on which yeast can work upon


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