An Investigation into how the varying concentration of a substrate affects the rate of reaction of Catalase.

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An Investigation into how the varying concentration of a substrate affects the rate of reaction of Catalase

In this investigation, I am going to explore how varying the concentration of Hydrogen Peroxide (HO) affects the rate of reaction of the enzyme, catalase.

Background Knowledge

Enzymes are organic catalysts. Catalysts are chemical substances that speed up a reaction but remain unaltered throughout the reaction. They are made in all living cells and control the chemical reactions that keep the cell alive as well as speeding up the metabolic processes. Enzymes are proteins and their molecules are made up of long chains of amino acids.

Enzymes can be divided into two groups. Intracellular enzymes occur inside cells and control metabolism. Extra cellular enzymes are produced by the cells and achieve effects outside the cell. E.g. digestive enzymes.

  • Enzymes are specific which means that an enzyme that acts on one substance won’t act on another. The substance an enzyme reacts with is its substrate. They fit together like a lock and key. The place where the molecule fits into is called the active site. When the substrate is inside the enzyme it’s called an enzyme substrate complex.

The enzyme breaks the substance into smaller molecules called products. These are produced when the reaction has finished. The enzyme remains the same and so can be used again.

  • Enzymes work very rapidly and the speed of action of an enzyme is called its turnover number. By this I mean, the number of substrate molecules which one molecule of the enzyme turns into products per minute.
  • They can work in either direction.
  • Enzymes are inactivated by excessive heat. They work best at an optimum temperature (40°C) and if this temperature is exceeded the enzymes become denatured. Denatured means that the chains of amino acids holding the enzyme together break and so it loses its shape irreversibly. Therefore the substrate no longer fits into the active site and the enzyme activity will stop.
  • Enzymes are sensitive to ph. The optimum ph is 7. Excessive acidity or alkali makes them inactive.

The rate of an enzyme-controlled reaction depends on the temperature and the concentrations of the enzyme and its substrate. To work out the rate of reaction you do: Amount of product

                            Time taken

Temperature

If you increase the temperature, the rate of reaction will be quicker. This is because the molecules have more kinetic energy and so the molecules vibrate quicker and with more force so there is more chance of the molecules colliding and reacting.

After the optimum temperature (40°C) the enzymes will become denatured and so the rate of reaction will slow down and eventually cease.

The graph would look like this:

Concentration of enzyme

If you increase the concentration of the enzyme, the rate of reaction will be quicker. This is because there is more enzyme and so more molecules per cm³, which means there’s a higher chance of he molecules colliding with the substrate molecules. Therefore the substrate will be broken down into products quicker. After a certain amount of time the rate of reaction will reach a plateau because the enzyme has run out of substrate to break down.

The graph would look like this:

Rate of reaction 

cm³/ minute

Concentration of substrate

If you increase the concentration of the substrate, the rate of reaction will be quicker because the more concentrated the molecules are, the more densely packed they are and so are more likely to collide and react. The rate of reaction will reach a plateau when there are higher concentrations because the active site of the enzyme becomes saturated so as soon as one substrate molecule is turned into products, the enzyme is immediately taken up by another substrate molecule. Therefore the enzyme is working as hard as it can so the rate of reaction can’t increase anymore.

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In this experiment I am going to use the enzyme catalase. Catalase is the fastest known enzyme and has a turnover number of 6 million. Catalase is specific to reacting with Hydrogen Peroxide. It decomposes the poisonous hydrogen peroxide into water and oxygen, which are harmless.

catalase    +       H₂O₂            catalase        H₂O    +       O₂

The catalase is the same at the end of the reaction as it was at the beginning.

Plan

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