Factors Affecting Enzyme Activity

Factors Affecting Enzyme Activity
There are thousands of biological processes and chemical reactions that take place in the body every day, and so the body requires a huge amount of energy to deal with this high demand of activity. In most cases the energy requirement would be too large, and so cells use enzymes to help with reactions in the body. Enzymes are a highly renewable source as they do not get used up themselves, meaning that they are biological catalysts, and are highly affective as they greatly reduce the amount of energy needed for a reaction, whilst at the same time making the reaction take place in a shorter space of time. [image]The liver is a vital organ of the body, and has hundreds of functions. The typical liver cell contains many organelles called peroxisomes, shown on the right, which oxidise fatty acids and detoxifies alcohol, amongst other processes.
Enzymes in peroxisomes work by transferring a Hydrogen atom from a substrate to an Oxygen atom. However, although this process is breaking down harmful substances, it also creates H2O2, or hydrogen peroxide, which is a very toxic and dangerous compound, so much so that white blood cells use it in small amounts to kill harmful bacteria. This byproduct therefore must be removed or it will cause damage to the cell. The peroxisomes therefore contain another enzyme called catalase, which breaks down the hydrogen peroxide into water and oxygen gas due to this equation: [image]2H2O2 Catalase 2H2O + O2 One molecule of catalase can break down around 6,000,000 molecules of hydrogen peroxide a minute, and the cell can reuse the products of this reaction, which means that this is a very efficient way of reducing waste. The most common factors that influence an enzyme?s rate of reaction are pH levels, temperature, and the concentrations of the enzyme and the substrates. Concerning pH levels, any enzyme will become denatured if its environment differs too greatly from its optimum pH level. Any enzyme will also become denatured it its surroundings reach a temperature of 40-50?C and above, as body temperature is around 36?C, which, through adaptation, would therefore be an enzyme?s optimum temperature. An increase in the concentrations of the substrate or the enzyme will expectedly be in direct proportion to the rate of reaction in a positive sense, i.e. the higher the concentration, the higher the rate that the products of reacting hydrogen peroxide with catalase will be. Aims ? To acknowledge the effect of the concentration of the enzyme catalase on its decomposition of hydrogen peroxide. ? To acknowledge the effect of the concentration of hydrogen peroxide as a substrate in its decomposition, due to the enzyme catalase. Method Refer to method sheet. Changes include: In exercise 2 ? put 20vols H2O2 in boiling tube A, 16vols in tube B, and so on with 4vols in boiling tube E. Results Tabulated results for Exercise 1: The Effect of Enzyme Concentration on the rate of Reaction. Time taken for O2 bubbles to reach: Pieces of Liver 5cm up the boiling tube (s) 10cm up the boiling tube (s) 1 = approx. 27 mm3 4.9 9.6 2 = approx. 54 mm3 2.9 5.1 3 = approx. 81 mm3 1.5 3.6 4 = approx. 108 mm3 1.1 3.0 5 = approx. 135 mm3 0.6 1.3 Tabulated results for Exercise 2: The Effect of Substrate Concentration on the Rate of Reaction. Tame taken for O2 bubbles to reach: Concentration of H2O2 (Vols) 5cm up the boiling tube (s) 10cm up the boiling tube (s) Number 1 = 20vols 0.6 1.2 Number 2 = 16vols 1.5 3.5 Number 3 = 12vols 2.1 4.9 Number 4 = 8vols 3.2 Did not reach 10cm mark Number 5 = 4vols 4.1 Did not reach 10cm mark Discussion In the first exercise, where it was the effect of the concentration of the enzyme catalase observed, there is a definite trend in the results. As the concentration of catalase increased, the time taken for oxygen bubbles to reach 5cm and 10cm marks decreased. Because of this direct correlation, we can say that the concentration of enzyme is in direct proportion to the rate of reaction. This is because of a simple theory, whereby the higher the concentration of a substance, the more molecules of that substance there is, in this case catalase, and therefore there is a higher chance of enzyme-substrate complexes, and hence the reaction takes place in a shorter space of time. This theory also applies to the second exercise, where it was the effect of the substrate hydrogen peroxide?s concentration on the rate of reaction. Here the results also show that there is a direct correlation between the concentration of hydrogen peroxide and the time taken for oxygen bubbles to reach 5cm and 10cm up the boiling tube. The higher the concentration of the substrate, the higher the density of H2O2 molecules, and therefore there is a greater likelihood of enzyme-substrate complexes, and so the reactions are quicker. Although the results obtained are concordant with scientific principles concerning the concentrations of substances and the rate of reactions between them, the results are not very accurate. This is largely due to human error, as some of the reactions that took place were very quick, e.g. 0.6s for the O2 bubbles from 20vols H2O2 to reach the 5cm mark, and so the inaccuracy of human reactions would delay the results. To overcome this, the test for each concentration of enzyme and substrate could be tested at least three times. This would mean that an average of concordant results could be obtained, thereby increasing the accuracy and reliability of the results. The main implication for the results being incorrect is that the rate of reaction cannot be found to an accurate degree. If a machine were used to measure the amount of product formed in each instance, then the results would be exact and therefore the rate at which catalase decomposes hydrogen peroxide could easily be deciphered. The experiments carried out insisted that variable components were controlled in order for the results to be as valid as possible. An influential factor in the rate of chemical reactions is the pH of the substances? surroundings. This was controlled as the reaction took place in a boiling tube and not an aqueous environment, therefore the pH ceased to be an issue. The temperature of the surroundings is also very influential upon the rate of reaction, as, according to the kinetic theory, the higher the temperature is the more kinetic energy the molecules have, which means they physically move around more. This therefore leads to a greater chance of collisions and enzyme-substrate complexes, leading to quicker reactions. However, no addition temperature was apparent and no temperature was taken away from the surroundings of the boiling tubes at the time of the experiment. Temperature was controlled at room temperature by keeping doors and windows closed as to not effect the rate of reaction. However, this is not the most reliable control, and so a controlled water bath may have been more suitable for this experiment as temperature can so easily influence this type of reaction. It would be interesting to control all other factors and measure the reaction?s optimum temperature, as we would estimate it to be around body temperature 36?C. The experimental influencing factor within the experiment was the concentration of the enzyme or substrate, depending on which was being tested at the time. This is because if the concentration of hydrogen peroxide varied when only the concentration of catalase was being tested, then the rate of reaction would be quicker in some of the tests than it should be because of the higher substrate concentration plus the addition of the higher enzyme concentration. Likewise for testing the effect of hydrogen peroxide concentration; a 5×5×5 cube of liver was used in each test of decreasing concentration of H2O2. However, although the pieces of liver were cut to around the same size and measured with a ruler, due to human error and inaccuracy it is likely that the amount of liver in each test tube were not exactly of the dimensions 5×5×5, and in the first exercise all of the pieces of liver were not accurately 3×3×3. A solution to this would not be to weigh the liver for accuracy, as it is the surface area that is in contact with the hydrogen peroxide and so is most important in relation to the speed of the reaction. Therefore accurate cutting using a machine would be necessary for further accuracy. Conclusion From the results gained it can be observed that the higher the concentration of the enzyme catalase, or the higher the concentration of the substrate hydrogen peroxide, the higher the rate of reaction. This direct relationship is due to the rule that the more concentrated two substances are, the more molecules there are of them in a given solution. Therefore there will be a higher chance of collisions between molecules, resulting in more enzyme-substrate complexes and therefore giving higher rate of reactions.

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