The effect of concentration on the activity of catalase.

Title:

Brief Introduction:

This experiment will look at the effect of varying the concentration of the enzyme, catalase on its performance. Potato will be the source of catalase.

Hydrogen peroxide is a toxic substance that may be formed during aerobic respiration. It must be removed from the system and catalase breaks it down into harmless substances. The equation for the reaction is:

2H2O2 → 2H2O + O2

Hypothesis:

Increasing the concentration of the enzyme, catalase will increase the volume of oxygen produced per unit of time.

The nature of the problem to be investigated is the factor that is effecting the rate of the reaction and what effect this factor will have on the rate of reaction when it is increased. In this investigation, the factor effecting the rate of the reaction is the concentration of the enzyme. Increasing the concentration of the enzyme, catalase will increase the volume of oxygen produced per unit of time. The reason for this is as follows.

For a chemical reaction to take place, the substrate molecules must collide with the enzyme molecules and to be specific, must result in a successful collision. This is called the collision theory. Increasing the enzyme concentration will increase the number of molecules. This will increase the frequency of collisions and increase the chance of successful collisions. This will in turn increase the rate of the reaction.

Null Hypothesis:

Increasing the concentration of the enzyme, catalase will have no effect on the volume of oxygen produced per unit of time.

Aim:

To investigate the effect of varying the concentration of the enzyme, catalase, on the rate of reaction. The volume of oxygen produced per unit of time will measure to indicate the rate of the reaction.

Prediction:

The prediction for this investigation is that the volume of oxygen produced per unit of time increases with the increasing concentration of catalase. The justification for this prediction is stated in the hypothesis. Figure 7 shows the predicted graph.

Background Information:

The majority of enzymes are proteins. An enzyme is a biological catalyst. It increases the rate of a reaction without itself being involved in the reaction. The properties of enzymes are:

The enzymes are still efficient in small quantities.
The enzymes are specific to their reactions.
They remain unchanged at the end of a reaction.
They lower the activation energy.
They have an optimum temperature after which point, they become denatured. This is due to the energy breaking down bonds.
They also have an optimum pH after which they become denatured.

Enzymes work by a lock and key mechanism. The substances, which combine to the enzyme, are called the substrate. The particular area on the enzyme, which the substrate combines to, is called the active site. The shape of the substrate is complementary to the shape of the active site. This explains why enzymes are specific to their reactions. It is now found that in some enzymes, the active site changes when the substrate attaches to it. This is for a more accurate fit. This is called the induced fit. When the active site and the substrate join, it forms an enzyme-substrate complex. Once the product has been formed, it leaves the active site leaving it free to combine with another substrate molecule. This experiment looks at the effect of increasing the concentration of the enzyme on the rate of reaction. Increasing the enzyme concentration will increase the number of active sites. This increases the turnover of enzyme-substrate complexes formed and thus the formation of the product. Figure 2 illustrates the action of enzymes.

The rate of a reaction means the speed at which a reaction occurs. Reactions have different rates. There are factors that determine the rate. These are:

Temperature
Concentration
Light (only in certain reaction)
Catalyst
Surface area
Pressure

The theory that explains how these factors effect the rate is called the collision theory.

All matter is composed of particles that are constantly in motion. When two molecules react, bonds are broken or made and there often is a rearrangement of the atoms. According to the collision theory, for this to happen, the molecules must collide first. An effective collision must occur. An effective collision is the number of collisions that result in a reaction. The reaction rate can also be defined as a measure of how frequently effective collisions occur. This indicates that the number of effective collisions is proportionate to the rate of the reaction. There are two conditions that are applicable for an effective collision to occur. The molecule must approach each other and collide in the appropriate orientation. This is referred to as the steric factor. The molecules must also contain the minimum amount of energy for the reaction to commence. This is referred to as the activation energy. It is due to these conditions that not all collisions that occur result in an effective collision. If this were the case, all reactions would be instaneous. Reaction rates can therefore be increased if collisions occur more frequently and the percentage of molecules having the effective activation energy or greater is increased.

This experiment looks at the effect of concentration in the reaction between the enzyme catalase and hydrogen peroxide. Increasing the concentration increases the frequency of collisions between the reactants because there are more molecules in a given volume. This will increase the number of effective collisions and therefore the rate. Figure 1 illustrates the action of increasing the concentration.

The reaction of the decomposition of the hydrogen peroxide by catalase is a redox reaction. This experiment uses catalase as the enzyme. Catalase is an enzyme that is present in the cells of plants, animals and aerobic bacteria. It promotes the conversion of hydrogen peroxide into harmless substances. Hydrogen peroxide is decomposed in to water and oxygen. Catalase can be detected in a sample by adding hydrogen peroxide to it. If the sample contains catalase, it will foam and produce bubbles. The bubbles are oxygen being evolved. Catalase is present is the perioxsomes of nearly all aerobic cells. Perioxsomes are membrane bound organelles that is the location of various oxidation reactions whereby toxic peroxides are produced as side products. Catalase’s function is to protect the cells from hydrogen peroxide’s damaging effects by decomposing it in to oxygen and water.

The primary structure of catalase is the monomers that join the quaternary structure. The primary structure of catalase consists of five hundred and six amino acids that forms a polypeptide chain. It also contains a heme group and one NADH molecule. The heme group consists of a ring structure and a central iron atom. Catalase functions by the oxidation of iron without the heme group. The heme group is similar to those in the hemoglobin in the alveoli. The primary structure of catalase also contains an NADH molecule. NADH is a molecule that supplies the activation energy needed to turn the nourishment needed for life into energy. Nourishment is things such as glucose from digested food and oxygen. The energy formed is then used for respiration. NADH is obtained from your diet. In the quaternary structure of catalase, each molecule is a tetramer of four identical polypeptide chains. Each polypeptide chain consists of more then five hundred amino acids. The protein exists as a dumbbell shape. The structure of catalase is shown in figure 3.

Hydrogen peroxide is decomposed by catalase. Hydrogen peroxide is a strong oxidising agent. Hydrogen peroxide is made up of the same elements as water and has a similar molecular formula to water except hydrogen peroxide has an extra oxygen atom and it is this factor that makes it a strong oxidising agent. Hydrogen peroxide is a natural metabolite in many organisms that carry out aerobic respiration. Hydrogen peroxide kills bacteria, viruses and fungi because it is a strong oxidiser. It is made in the body to fight infection. It is necessary for our immune system to perform properly.

Neutrophils produce hydrogen peroxide as their main defense mechanism against toxins, parasites, bacteria, viruses and yeast. Neutrophils contain granules that are able to digest a variety of cellular materials. When a bacterium is engulfed by a neutrophil, the cell surface membrane invaginates in endocytosis and forms a phagocytic vacuole. The granules are released into the vacuole containing the organism. A metabolic process within the granules produces hydrogen peroxide, which destroy the ingested bacteria. Hydrogen peroxide has many advantageous uses in industry. Figure 4 shows some of them. Figure 5 shows a molecule of Hydrogen peroxide.

...