Conclusion:
In my experiment I investigated how changing the temperature of the enzyme peroxidase (using green beans as a source) affects its rate of activity with hydrogen peroxide, as measured by the volume of oxygen gas produced.
Our results show that changing the temperature of green beans does affect the activity of the peroxidase enzyme. From 3 degrees to 30 degrees the activity (as indicated by oxygen production) increased rapidly, with the rate increasing from 0.098 to 0.35 mL s-1 however past this temperature the enzyme began to decrease to a minimum of 0.017 mL s-1. The error bars for my data are reasonably consistent, however the size of the error bar appears to increases as the rate value increases, from a minimum size of ±0.016 at our second lowest rate of 0.098 mL s-1 which was recorded at 3 degrees to a maximum of ±0.035 at our highest rate of 0.35 mL s-1 recorded at 30 degrees. The curve of best fit is reasonably accurate and it passes through all of the error bars. This indicates that the trend indicated by the line is accurate.
We had very few outliers, with only one notable one which occurred at 80 degrees when we recorded a result of 7mL of oxygen being produces while the other results varied from 0-2mL, this would have increased our mean rate value at this temperature, potentially causing our graph to be less steep than expected.
The effect of temperature on the rate of activity of the peroxidase enzyme is explained through Brownian motion and enzyme theory. Green beans like other living organisms it utilise enzymes to facilitate/catalyse reactions and thus increase the rate of biological processes, without being used up themselves.
In our experiment the peroxidase enzyme is used to catalyse the conversion of toxic hydrogen peroxide into oxygen and water. Thus we assume that oxygen production is an indication of peroxidase activity, as under normal conditions the conversion would occur at such a slow rate that no affect would be visible without the addition of the enzyme. All plants contain peroxidase as it is needed to ensure that toxic hydrogen peroxide is broken down into harmless products ensuring no negative impacts on the cell. The conversion of hydrogen peroxide is shown though the following equation:
2 H2O2 → 2 H2O + O2
Enzymes are proteins with unique shapes, which are capable of binding with substrates to form enzyme substrate complexes. Enzymes have specific binding sites which causes enzymes to be substrate specific.
“The binding between enzyme and substrate(s) consists of weak, non-covalent chemical bonds, forming and enzyme-substrate complex that exists for only a few milliseconds. During this instant, the covalent bonds of the substrate(s) either come under stress or are oriented in such a way that facilitates the formation of a different molecule or molecules. This results in the formation of a product. The product leaves the enzyme’s active site and is used by the cell. The enzyme is unchanged by the reaction and may enter the catalytic cycle again if more substrate molecules are available.”
Figure 1: Sourced from http://www.studyblue.com/notes/note/n/microbial-metabolism-/deck/10602
The rate that enzymes and substrates collide is explained by principles of chemical kinetics, a branch of science which is concerned with the dynamics of chemical reactions: the way reactions take place and the rate (speed) of the process. The two theories which relate to this experiment is the ‘kinetic theory of matter’ and ‘collision theory’. The kinetic theory of matter, states that particles more in a random continuous way which is proportional to the amount of kinetic energy of the particle. For an enzyme substrate to be formed the enzyme and the substrate must collide with the correct orientation and sufficient kinetic energy. This leads on to ‘collision theory’ which states that for the rate of reaction to increase there must be more frequent collisions caused by an increase in speed or in number of particles, as the temperature is being increased the kinetic energy is also increasing and the speed of the particles will increase. Causing the reaction to speed up, and thus rate of activity will increase and more gas is will be produced, explaining our original increase.
However, increasing temperature can have an adverse effect on enzymes as most enzymes consist of a protein and a non-protein (called the cofactor) and the intra- and intermolecular bonds that hold proteins in their structures can be disrupted by changes in temperature. This occurs when the temperature exceeds too far past the optimum temperature. Optimum temperature for enzymes is the temperature where enzyme activity is at its greatest. However “above this temperature the enzyme structure begins to break down (denature)” (in our results would be approximately the temperature where our maximum rate value of 0.35 occurred, at 30 degrees). If the bonding of the enzyme is affected then the shape of the molecule will be altered and thus the shape of the active site will be alters meaning the substrate will not be able to bind. And thus the rate of enzyme activity as indicated by oxygen gas production, will decrease. The effect of temperature is illustrated in the graph above.
Different enzyme have different optimum temperatures, and thus the optimum temperature of humans, 37 degrees, is different to that of green beans which is typically lower due to average climatic conditions that green beans face.
Our results are supported by a article published in Plant Physiology and Biochemistry which investigated the “effect of pH and temperature on peroxidase and polyphenoloxidase activities of litchi pericarp”. Their graph shows a similar parabolic trend to our own, as the points steadily increase to a maximum and rapidly decrease. However our maximum was at a lower temperature but this experiment was conducted using Litchi instead of green beans, thus a different optimum temperature is expected.
It is important to understand the science behind this as without enzymes to convert toxic hydrogen peroxide into non toxic materials plants may not survive resulting in life not be sustainable on earth, plants also play a hugely important role in the agriculture and food industry.
Evaluation:
https://www.dcccd.edu/SiteCollectionDocuments/DCCCD/Docs/Departments/DO/EduAff/Core/Assessment%20Methods/Enzyme_lab%20report_final.pdf
http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-90162010000200013
http://ijche.com/issues/2010-7-2/42.pdf
http://www.plantphysiol.org/content/68/6/1395.full.pdf
http://ijche.com/issues/2010-7-2/42.pdf
http://www.medical-and-lab-supplies.com/bd-cornwall-disposable-syringe-system-10ml-size.html#
https://proscitech.com/?navaction=show_page&chapter=t&page=6#tcv3-03