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Investigate the effect of varying substrate concentration in an enzyme reaction involving catalase from vegetables and Hydrogen Peroxide.

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Introduction

L6 Enzyme Coursework PLANNING Enzymes Enzymes are protein structures that bond to the reactants in the reaction in which they are involved and thus lower the amount of activation energy required making the reaction more efficient and therefore speeding it up. Enzymes work when their corresponding substrate fits into their active site and touches all the contact points thus indicating to the enzyme that it is the correct substrate. This is known as the lock and key mechanism and ensures that the correct enzymes match to the correct substrates however it is vulnerable to competitive and non competitive inhibitors which latch onto the enzyme by bonding themselves to it weakly and slow down the reaction. Their protein composition means that they are vulnerable to denaturing in high temperatures. Lock and Key Mechanism Here we can see how the specific substrates fit with the specific enzyme by having corresponding shapes. The active site of the enzyme can be seen as the lock while the shape of the substrate/s can be seen as the key. Competitive inhibitors work by competing with the substrate for the active site of the enzyme. They often have the same shape as the substrate and so the enzyme spends time breaking down the competitor and not the substrate, this slows the reaction. Non competitive inhibitors bond with the enzyme in an area other than the active site. Their subsequent attachment to the enzyme changes the shape of the hydrogen bonds within the enzyme and changes it shape making it useless. Aim The aim is to investigate the effect of varying substrate concentration in an enzyme reaction involving catalase from vegetables and Hydrogen Peroxide. Method Using different proportions of 2% Hydrogen Peroxide solution and Buffer, make up about five concentrations in five PONY vials. Cut a slice of Radish, and using tweezers place a single filter paper disc onto the freshly cut side for five seconds, then soak the other side of the disc on the freshly cut side for another five seconds. ...read more.

Middle

Much more accurate than syringes Stopwatch Timing Allows accurate Timing. Filter Paper Discs Absorption of Catalase Absorbs Catalase and then can be used in reaction PONY vial Container for reaction Clear so allows reaction to be observed easily Razor Blade Trim plant material Allows small cuts so as radish can be used as much as possible. Very precise. Analysis Table of results for final experiment Concentration of Hydrogen Peroxide (%) Vol. of Buffer (cm�) Vol. of Hydrogen Peroxide (cm�) Time 1 (s) Time 2 (s) Time 3 (s) Average time (s) 6.0 0 5 1.25 1.26 1.24 1.25 4.0 1.6 3.3 1.31 1.31 1.32 1.31 2.0 0 5 1.47 1.48 1.37 1.44 1.6 1 4 2.48 3.01 2.79 2.76 1.2 2 3 4.22 4.18 4.94 4.45 0.8 3 2 5.95 6.27 6.03 6.08 0.4 4 1 7.24 6.19 6.42 6.61 N.B. as you can see, the top two rows of volume proportions are not corresponding to those below them. The concentration of the Hydrogen peroxide was tripled for these particular tests so that the reaction could be observed with a much higher concentration thus expanding the scope of results obtained. The graph of the results following the analysis shows that as the concentration of hydrogen peroxide increases, so does the rate of reaction thus proving my initial prediction correct. However, when the substrate concentration begins to increase further, it has a lesser effect on the rate itself. This is enzyme saturation (V-max) where the enzymes cannot work any faster and rate of reaction peaks. This is why we see the line in the graph levelling off. According to the collision theory, as substrate concentration increases, the number of particles present in the solution obviously increases. The likelihood of frequent and successful collisions between enzyme and substrate particles is greater, rate increases and so the reaction is carried out in a smaller time. A lower substrate concentration means less particles present and so the frequency and likelihood of a successful collision is decreased and thus the rate also. ...read more.

Conclusion

The resistance of the motion due to its position meant that times would vary thus hindering or promoting the rate. Usually the rate was promoted when the disc would float to the top in a vertical position giving least resistance and thus increasing the rate of reaction. This would account for the one anomalous result noted in the experiment. One set of anomalous results was obtained and I believe this was due to inaccurate measuring of solutions for one particular concentration of hydrogen peroxide. Their presence was not crucial to the experiment and the particular results were therefore left out of the graph and trend line. Other than for the set of anomalous results the rest of the measuring would appear to have been done accurately using marked syringes, one for each solution so as not to mix them and affect results. The results obtained were reliable, even the error bars which were small were very close to the trend line. Larger error bars would suggest a less accurate and reliable experiment with very variable results where as smaller ones would suggest a much more accurate experiment. I don't believe my trend line would be greatly affected if my error bars were smaller. A changed trend line would probably change the possible conclusions drawn but this does not apply to my experiment. In conclusion I can say that my initial prediction was right and that the rate of reaction increases with a greater substrate concentration. It is clear in the results table and graph that this is true. It was also proved right that enzyme saturation (V-Max) would occur when a significantly large amount of substrate was used in the test and this is shown in the graph where the line levels out towards the higher concentration of Hydrogen Peroxide. I am confident that my results are correct because the Rs value worked out in the analysis was 1 which signifies a perfect correlation of results. The fact that it is a positive number also shows that there is a positive correlation as was predicted. ...read more.

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