Investigating the effect of substrate concentration on reaction between Hydrogen Peroxide (H2O2) and the enzyme Catalase.

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Biology Coursework

Ismail Lakhi

Investigating the effect of substrate concentration on reaction between Hydrogen Peroxide (H2O2) and the enzyme Catalase

AIM

Catalase is an enzyme found in Yeast, and when yeast reacts with H2O2, a reaction occurs, with H2O2 acting as the substrate, and Catalase being the complementary enzyme. In this experiment, I will analyse, interpret, conclude and evaluate the effects of reacting different concentrations of H2O2 with the enzyme Catalase and hence, use it to understand the effects on the rate of the reaction. My main aim is to understand how enzymes work under varied conditions.

Yeast is not a chemical and has no chemical formula.  Try looking at yeast

as a single cell, similar to any single cell in your body.  Those cells

are made up of numerous types and classifications of chemicals.  Some are

very simple, like water.  Others are extremely complex, like proteins. As the enzyme Catalase is not available in pure form, I will use yeast as the source of enzyme. There are other alternatives e.g. potato tubes which also contain catalase, but using yeast would give me greater accuracy because the amount of Catalase in each potato tube would be different.

BACKGROUND INFORMATION

Enzymes are biological catalysts, which means that they speed up biological reactions without getting used up themselves. They also provide a control mechanism for reactions, as the amount of enzyme available determines how quickly a reaction can happen.

Enzymes are globular proteins that have a specific shape. They contain a ‘depression’ called the ‘active site’ and this is the main area for reactions to occur. The ‘substrate’ is what the enzyme acts on and breaks down. Enzymes are ‘specific’ because their active sites have specific shapes and only substrates that have a complementary shape can fit into the enzymes active site, thus causing a reaction.

There are 2 theories, which describe the way enzymes function:

  1. The Lock and Key Theory

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Enzyme          +        Substrate                                  Enzyme Substrate

                                                                      Complex

Enzyme molecules are constantly moving about within a cell and when an enzyme molecule collides with a substrate molecule, the substrate binds to the enzyme’s active site. Together, they form an ‘enzyme-substrate’ complex (as shown in the above diagram). The substrate reacts within this complex to form the product, which then leaves the active site. The enzyme is not changed at all in this reaction and is now free to react with any other substrate molecules it collides with. It is called a ‘lock and key’ mechanism because the enzyme acts in a similar manner to a ‘lock’ and the substrate is the ‘key’.

  1. The Induced fit Hypothesis

    +

        Enzyme            +           Substrate                                Enzyme-Substrate                                                                                Complex

This theory suggests that the enzyme’s active site is similar in shape to the substrate, but not fully complementary to it. When the substrate approaches the active site of the enzyme, the shape of the active site changes to accommodate that substrate i.e. it ‘induces a fit’. The substrate can now bind to the active site and a reaction can take place.

For a reaction to occur the 2 substances must collide with each other and a certain amount of energy is required to make this happen. This energy is called ‘the activation energy’ and is needed to overcome the energy barrier. An enzyme catalyses a reaction by lowering the activation energy, so less energy is needed for the reaction to take place. The graph below shows the difference between activation energies in a reaction when there is an enzyme present and when there is no enzyme present:

As the diagram shows, in the presence of an enzyme, the activation energy is lowered considerably so the reaction occurs quicker.

Structure of an Enzyme

Enzymes are proteins, and how an enzyme functions depends on its 3D structure. The shape of the active site is most important because it gives an enzyme its specificity. The picture on the left shows a very simplified active site. Weak bonds hold it together. This is called its tertiary structure.

When these weak bonds are broken, the tertiary structure of the active site changes drastically. The shape of the active site is changed so the enzyme can no longer act as a catalyst. The enzyme is said to be denatured.

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Factors that affect the of an enzyme

There are 3 main factors that affect the rate of reactions of enzymes:

  1. Temperature
  2. pH
  3. Concentration of enzyme/substrate

Temperature:

At low temperatures, the enzymes and substrates have low kinetic energy so they are moving around slowly and only a few reactions occur. When the temperature is increased, the Kinetic Energy also increases; therefore, the enzymes and substrates have more energy so they move around faster. More movement leads to more collisions between enzymes and substrates; thus, more enzyme-substrate complexes can be formed. ...

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