The Effect Of Varying Enzyme Concentration On The Breakdown Of Hydrogen Peroxide In The Presence Of Essay
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Hypothesis – Hydrogen peroxide will breakdown to oxygen and water in the presence of Catalase. The reaction will increase with increasing enzyme concentration when molecules of hydrogen peroxide are freely ...
Variables ;In this investigation, the variables that affect the activity of the enzyme, Catalase, were considered and controlled so that they would not
align=center>Research Enzymes exist in all living things. They are composed of polymers of amino acids and are produced in living cells. Each cell contains several hundred enzymes, which catalyse ...
i) Temperature ;As temperature increases, molecules move faster (kinetic theory). In an enzyme catalysed reaction, such as the decomposition of hydrogen peroxide, this increases the rate at which the enzyme and substrate molecules meet and therefore the rate at which the products are formed. As the temperature continues to rise, however, the hydrogen and ionic bonds, which hold the enzyme molecules in shape, are broken. If the molecular structure is disrupted, the enzyme ceases to function as the active site no longer accommodates the substrate. The enzyme is denatured.
To control this variable, the temperature was maintained at a fairly constant level that allowed the enzyme to work effectively (room temperature, approximately 23ºC). This was achieved by using a test tube rack and tongs to handle the apparatus so that the heat from my hands did not affect the Catalase.
ii) pH ;Any change in pH affects the ionic and hydrogen bonding in an enzyme and so alters it shape. Each enzyme has an optimum pH at which its active site best fits the substrate. Variation either side of pH results in denaturation of the enzyme and a slower rate of reaction.
In this experiment, the pH was kept constant using a pH 7 buffer, selected to maintain a pH level suited to the enzyme by being equal to the natural environment of the enzyme (potato tissue).
iii) Substrate Concentration ;When there is an excess of enzyme molecules, an increase in the substrate concentration, produces a corresponding increase in the rate of reaction. If there are sufficient substrate molecules to occupy all of the enzymes´ ;active sites, the rate of reaction is unaffected by further increases in substrate concentration as the enzymes are unable to break down the greater quantity of substrate.
To control the substrate concentration, identical quantities of the substrate were used for each reading. To ensure that this was measured precisely, 5ml syringes were used to accurately gauge to exact quantities.
iv) Inhibition ;Inhibitors compete with the substrate for the active sites of the enzyme (competitive inhibitors) or attach themselves to the enzyme, altering the shape of the active site so that the substrate is unable to occupy it and the enzyme cannot function (non-competitive inhibitors). Inhibitors therefore slow the rate of reaction. They should not have affected this investigation, however, as none were added.
v) Enzyme cofactors ;cofactors are none protein substances which influence the functioning of enzymes. They include activators that are essential for the activation of some enzymes. Coenzymes also influence the functioning of enzymes although are not bonded to the enzyme.
Unless enzyme cofactors were present in the potato tissue containing the Catalase, they were not included in this investigation and therefore would not have affected the rate of reaction and the results of this experiment.
vi) Enzyme Concentration ;Provided there is an excess substrate, an increase in enzyme concentration will lead to a corresponding increase in rate of reaction. Where the substrate is in short supply (i.e. it is limiting) an increase in enzyme concentration has no effect.
I varied the enzyme concentration by altering the number of equal sized discs of potato that contain the Catalase, in the reaction. The greater the number of discs, the greater the enzyme concentration.
i) A manometer ii) 30ml hydrogen peroxide
iii) Manometer fluid iv) 6 boiling tubes
v) Tongs vi) A test tube rack
vii) A potato viii) A petri dish
ix) A cork borer x) Distilled water
xi) A razor blade xii) A stop watch
xiii) A ruler xiv) Rubber tubing
xv) A marker pen xvi) A clamp
xvii) A stop watch xviii) 2 5ml syringes
xix) pH 7 buffer xx) A bung
Procedures ;Three tubes, 10mm in diameter were bored from a potato using a cork borer. Using a razor blade and a ruler, 122 discs, 1mm thick, were cut from the tubes and placed under distilled water in a petri dish. This prevented the potato from being contaminated or dehydrated.
5ml of hydrogen peroxide and 5ml of a pH 7 buffer were then measured and added to each of six boiling tubes using a syringe. Care was taken to view the syringes from the side to ensure the bottom of the meniscus was lined up properly with the gradations and there were no air bubbles in the syringe. A pH buffer was added to the boiling tubes to maintain the pH at a constant level so that changes in pH as a result of the reaction would not affect the activity of the enzyme and disrupt the results. pH 7 buffer was selected to match the natural pH of the potato tissue and therefore suit the enzyme so that it could work efficiently.
One of the boiling tubes was then connected to a manometer containing manometer fluid using a bung (see diagram below). Holding the manometer level by the bung to ensure that the fluid was at its lowest level, a mark was drawn to indicate this point using a marker pen. A further mark was then drawn 5cm above the original, measured using a ruler.
15 pieces of potato were placed in to the boiling tube using a pair of tweezers to prevent contamination. A clamp was then placed over the rubber tubing on the bung to ensure that all of the oxygen gas released will travel up the manometer tube and not escape. Once the clamp was closed, the stopwatch was started to record the time taken for the manometer fluid to travel to the second mark. When this had been achieved the time was noted in a results table and the clamp opened to allow the gas to be released and the manometer fluid to return to its original level. Once the apparatus had been reset and any air bubbles in the manometer fluid removed, a second and later third reading was taken by re-closing the clamp and measuring the time taken for sufficient gas to be released from the reaction to force the manometer fluid back up to the top mark. By taking several readings for each enzyme concentration, it enabled me to average the results to minimise the extent of any inaccuracies. The experiment was then repeated for different quantities of potato discs (enzyme concentration) by using different boiling tubes containing hydrogen peroxide (see table below for quantities). I began with an enzyme concentration of 15 potato discs rather than a lower quantity to ensure that the apparatus was working correctly.
Vol. pH buffer (ml) Vol. Hydrogen peroxide (ml) No.Potato discs
5 5 5
5 5 10
5 5 15
5 5 20
5 5 25
5 5 30
5 5 35
Observations and Measurements ;In the boiling tubes it was clear that a reaction was taking place by the observation of bubbles of oxygen gas being released creating a fizzing´ ;in the boiling tubes.
In order to decide how varying the enzyme concentration affected the decomposition of hydrogen peroxide, the rate of reaction was measured. To do this accurately, the time taken for a specific quantity of oxygen gas (a product of the reaction) to be released was determined. This was achieved by observing the time taken for the manometer fluid to travel between the two marked fixed points as it was forced through the manometer by the rising gas. This was an accurate measure of how the enzyme concentration influenced the breakdown of hydrogen peroxide, as the quantity and speed of gas produced is dependant on the rate of reaction. The marked points remained the same distance apart for each reading for different enzyme concentrations so that they could be accurately compared and the trend observed.
All measurements were taken so that the stopwatch was started once the rubber tubing was sealed and the stopwatch stopped once the manometer fluid had reached the base of the highest marked point. To judge accurately, the point at which the fluid reached the marked line, it was examined at eye level and the measurement taken when the bottom of the meniscus was lined up to the mark. This was the same for every reading.
Data handling ;The data obtained from this investigation has been recorded in a table showing the time, enzyme concentration and rate of reaction. This means that the results of the experiment are presented in a clear and orderly fashion that allows patterns in
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