Investigating the Effect of Ph on the Activity of the Enzyme Catalase.

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Investigating the effect of pH on the activity of the enzyme catalase.


Hydrogen peroxide (H2O2) is a very pale blue liquid which appears colourless in a dilute solution, slightly more viscous than water. It is a weak acid. It has strong oxidizing properties and is therefore a powerful bleaching agent that is mostly used for bleaching paper.

Catalase is a common enzyme found in all living organisms. Its functions include the conversion of Hydrogen Peroxide, a powerful and potentially harmful oxidizing agent, to water and oxygen. One molecule of catalase can convert millions of molecules of hydrogen peroxide to water and oxygen per second. Liver and other living tissues contain the enzyme catalase. Hydrogen peroxide, which is a harmful by-product of the process of cellular respiration is broken down if it builds up in concentration in the cells. If we use potato or other tissue containing this enzyme, we can use this to measure the relative influence of varying different factors on the activity of enzymes in living tissue, the factor I will be investigating in my coursework is the activity of pH.


The aim of my investigation is to find out how different pH’s will affect the enzyme activity and how this will affect the rate of reaction. Extremely high or low pH values generally result in complete loss of activity for most enzymes. pH is also a factor in

the stability of enzymes. As with activity, for each enzyme there is also a region of pH optimal stability. I will also be measuring the rate at which oxygen is evolved and how it reflects the activity of the enzyme catalase.

Enzymes are generally globular proteins that have primary, secondary, tertiary and maybe quaternary structures. They are biological catalysts that can speed up a reaction rapidly. Enzymes are usually very specific as to which reactions they catalyse and the substrates that are involved in these reactions. Complimentary shape, charge and hydrophilic/hydrophobic characteristics of enzymes and substrates are responsible for this specificity therefore only one substrate will fit into the active site of the 1 enzyme.

Two theories on Enzyme function:

Lock and Key hypothesis - where you have 1 enzyme, 1 substrate and there is a complimentary shape and charge.

Induced Fit Hypothesis - The substrate and enzyme are not complimentary. During a collision the substrate induces a change in the active site shape and so it becomes complimentary. E.g. Hand in Glove.

Some enzymes are produced in an inactive form therefore need to be switched on by the addition of a non-protein group, this sometimes causes a permanent change.

Limiting factors- Few factors that affect enzyme activity

* Temperature

Each enzyme has an optimum temperature at which it works best. A higher temperature generally results in an increase in enzyme activity. As the temperature increases, molecular motion increases resulting in more molecular collisions. If, however, the temperature rises above a certain point, the heat will denature the enzyme, causing it to lose its three-dimensional functional shape by denaturing its hydrogen bonds. Cold temperature, on the other hand, slows down enzyme activity by decreasing molecular motion.

1. Rate of reaction is slow due to insufficient energy (kinetic), this means there are very few collisions between substrate and enzymes. 2. Rate of reaction increases due to more kinetic energy and more collisions. More

enzyme-substrate complex’s are formed.
3. It has now reached optimum temperature where there’s optimum energy. There are many successful collisions therefore more product has been formed. 4. Rate of reaction starts to decrease, The increase in kinetic energy now causes molecules within the enzyme to vibrate. This may result in the hydrogen bonds breaking therefore enzyme structure may change,. All the enzymes have still not been affected at this point and there has not...
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