Question: MAY, 2008a) What is an enzyme? (2) An enzyme is a protein which speeds up a chemical reaction i.e. a biological catalyst.
b) Explain, using diagrams, why an enzyme acts on just one particular substrate. (3) Enzymes have a specific site known as the active site. The active site has a specific ‘shape’ to which only a specific substrate will fit. When different substrates collide with an enzyme, only the substrate with a complementary shape will fit the enzyme. (Lock and Key hypothesis)
Properties of enzymes1. Enzymes are always proteins2. Enzymes are specific in their action3. Enzymes can be used all over again
Properties of enzymes4. Enzymes are destroyed (denatured) by heatProtein in egg white isdenatured by cooking.
Substrate CANNOT fit in active site Enzyme + Enzyme substrate denatured by heat or extreme pH Denatured enzyme cannot combine with substrate
Fig. 2 Graph to show the effect oftemperature on the rate of reaction. Enzyme becomes denatured above the optimum temperature.
Temperature Affects Enzyme Action: Little activity at low temperature Rate increases with temperature Most active at optimum temperatures (usually 37°C in humans) Activity lost with denaturation at high temperatures 18
Properties of enzymes5. Enzymes are sensitive to pH enzymes are denatured by extremes of pH Rate of reaction pH
Fig. 3 Graph to show the effect of pHon the rate of four different enzymes. What is the optimum pH of pepsin?
ONE use of enzymes Enzymes are obtained from bacteria and are used to make biological detergents.
Question: [SEP, 2010]a) Explain why biological detergents can only be effective when used in low temperatures. (2) Enzymes are proteins whose shape is affected by temperature. Above their optimum temperature, enzymes become denatured. The substrate does not fit in active site.
Question: [SEP, 2010]b) Give TWO environmental advantages associated with the use of biological washing powders. (4)1) No harm is done to the environment as they are natural products.2) As they work at low temperatures, there is no need to heat the water. Thus less fossil fuels need to be burned.
Two experiments:Effect of temperatureEffect of pH
Aim: To investigate the effect of temperature on the activity of amylase.