IGCSE Coordinated Science: Enzymes

Enzymes

1. Define enzymes as proteins that function as biological catalysts.

What is an enzyme? Enzymes are proteins, biological catalysts. Catalysts speed up rates of reactions (this is especially important for chemistry) Enzymes are also proteins that are folded into complex shapes that allow smaller molecules to fit into them. The place where these substrate molecules fit is called the active site.

2. Investigate and describe the effect of changes in temperature and pH on enzyme activity.

I’m going to break this into two parts, starting with temperature

Temperature change on enzymes : As temperature increases, so does the rate of reaction.

But only to a certain extent Raising the temperature to 900000 degrees, will frankly, not increase the rate of reaction.

• The graph above shows enzyme activity with increasing temperature. As we can see from the graph, enzyme activity generally increases as temperature increases, up to a certain point, which we call the “Optimum Temperature”. Basically, after this temperature, enzyme activity decreases with further increasing temperature.

  In humans, this is aroun 37C.

• Ph Effect on enzymes: Different enzymes work best at different Ph’s. For example, intestinal enzymes have an optimum Ph around 7.5, whilst enzymes in stomach has an optimum Ph at around 2.

3. Explain the effect of changes in temperature and pH on enzyme activity.

Effect of changes of temperature on enzyme activity:

1. The trick here is to get it to the “right” temperature. Too low, the substrate molecules of the enzymes do not have enough Kinetic Energy for the reaction to take place.

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Too high, and the intermolecular bonds (e.g. hydrogen) holding the structure of the enzyme (a protein) in place are easily broken by heat. Hence when an enzyme is heated up, these bonds break and the active site specificity of the enzyme is lost. Hence it becomes denatured and cannot participate as a catalyst. The enzymes breaks up and… you’re in a bit of trouble.

2. Effect of change of pH on enzyme activity: The pH is important because changes in pH away from the ‘ideal pH” can denature enzymes and cause changes in structure of enzyme, hence hindering the enzymes ability as a biological catalyst.