Enzyme Action Essay, Research Paper
Introduction “Enzymes are biological catalysts that carry out the thousands of chemical reactions that occur in living cells” (Eberhard, 1985). Enzymes are groups of proteins that are made of long chains of amino acids. They serve as catalysts by lowering the activation energy for chemical reactions. Cofactors and coenzymes are introduced when the enzyme needs help to catalyze the reaction. They are nonprotein helpers that bind to the active site; coenzymes are organic cofactors such as vitamins or vitamin derivatives. The substrate binds with the enzyme by fitting in its active site. When joined, the enzyme and substrate form the enzyme-substrate complex through hydrogen and ionic bonds. This is shown by the equation: E + S ES E + P. As shown, after the reaction, the enzyme is freed from the complex and may roam in search of more substrates to tackle. It is not used up but recycled. Conformation is a key issue for enzymes because each enzyme has a specific shape and active site that will work on specific substrates. Conformation results from the sequence of its amino acids, which determines its three-dimensional shape. Should the active site be blocked or changed, the enzyme will no longer serve the same purpose. Some changes may affect the entire activity of the enzyme, thus causing it to be denatured. Salt concentration is a factor that can denature an enzyme. If it is to low, then the enzyme will form a precipitate and become denatured. If, however, the concentration is too high, the interaction will be altered and hinder the enzyme again. The pH of the solution is also a factor of the rate of reaction. Amino acids have a tendency to lose or gain electrons, thus if the pH is lowered, the enzyme will gain too many H+ ions and have its shape disrupted; and if the pH is raised, the enzyme will lose H+ ions which also changes its active site. Most enzymes have their optimum at a neutral pH around seven, though some may work best in heavily acidic conditions. Buffers are compounds that help to prevent significant pH changes by giving up or taking in electrons without affecting the substrate or enzyme. Temperature changes may also denature the activity of an enzyme. Higher temperatures are usually better for enzymatic reactions because there are more collisions between molecules, however once the optimum temperature is reached, the enzyme becomes disrupted and denatured. Other small molecules known as activators and inhibitors affect the efficiency of an enzyme, though not completed in this lab.ExperimentIn the experiment we used the enzyme peroxidase from Pastinaca s.p. It was used to catalyze the oxidation of organic compounds, specifically guaiacol. We used guaiacol as an indicator of the reaction of H2O2 into H2O because it turns brown when it is oxidized. We also used a spectrophotometer to measure the amount of absorbance indicated by the amount of light passing through the solution. The rest of the experimental procedure can be found in the lab packet, Enzyme Acton. After the baseline run, the experiment was divided up into groups due to time constraints. I performed experiments one and three along with my partners. The turnip extract was given to us in the form of peroxidase. Data and Results For complete Data and Graphical representation refer to Tables 2.1-2.4 and Fig. 2.5-2.9 (Tables 2.1-2.4, Fig. 2.5-2.6 provided by Kay, 1998). The notable dip in the varying temperature graph can be accounted for by the “skewed” results of group ASMSJFGN at 22 degrees. Also other experimental errors caused the dip, as shown by data table, 2.2 (Kay, 1998). Other than that, most of the graphs are fairly comparable to theoretical results. Discussion It appears that most the experimenters were competent due to the results of the baseline, Fig 2.5 (Kay, 1998), which shows that the students understood how to use the spectrophotometers and provides some reliability to the rest of the experiment. The results from the turnip peroxidase concentration part of the experiment show that peroxidase concentration has a large effect on the rate of the reaction, Fig. 2.7. The double enzyme concentration has a rate, which is more than double that of the baseline reaction. This is due to the increased amount of collisions between the peroxide particles and the peroxidase enzymes. The results don’t appear to level off significantly, which shows that increased enzyme concentration will continue to result in an increase in the rate of reaction. The half enzyme concentration has nearly half the rate of reaction as the baseline, Fig. 2.7, which is a result of the diminished contact between the peroxide molecules and the active sites on the turnip extract.
The second part of the experiment, with the double and half substrate concentrations, demonstrates the effects of different peroxide concentrations. Fig. 2.8 shows that doubling the substrate concentration actually lowers the rate of reaction. Though this may appear contradictory because increased concentration would seem cause an increase in collisions and therefore an increased rate, however the increased peroxide molecules actually block one another from entering the active site on the peroxidase, causing the decrease in the rate. If the peroxide concentration continued to be increased; the reaction would reach a near halt. The half concentration part shows a decreased rate of reaction, which seems logical because there are less substrate molecules for the peroxidase to join with. Both the double and half substrate concentrations show that there is an optimum substrate concentration, at which the rate of reaction will reach its peak. However, the changes in the rate of reaction for the varying substrate concentrations are very little, as shown by the dependent scale on Fig. 2.8. Thus, this shows that substrate concentration doesn’t have a significant effect on the rate of reaction, at least not nearly as much as the enzyme concentration. The effects of varying temperature are the next part of the experiment. Temperature can be a denaturing factor at the wrong levels, as shown by the peak in the graph. (I explained earlier that the dip was cause by experimental error.) Before the peak is a constant curve, and after the peak, the curve should be a nearly constant negatively sloped curve. The Pastinaca parsnip extract actually reaches its peak, optimum temperature, at 22 degrees for guaiacol oxidation. After that, it appears as if the enzyme becomes denatured and loses efficiency. Boiling the enzyme completely denatures it and causes it to have no effect. As the kinetic energy increased, the randomness of the particles disrupted the enzyme’s ability to facilitate the reaction. The effects of varying pH are very similar to the effects of varying temperature. There is an optimum pH for the guaiacol oxidation, at which the maximum absorbance rate can be observed. Before and after this, the enzyme can be considered denatured, because of the lack of efficiency from the enzyme. The optimum pH appears to be just before 7, which a slightly acidic condition. I concluded that the turnip would actually grow best in a condition of 22 degrees and a soil pH of about 6.3. ConclusionI. Enzyme, turnip peroxidase, concentration is directly related to the rate of reaction. As the concentration increases, the rate increases; and when the concentration decreases, the rate also decreases.II. Substrate, peroxide, concentration has minimal effects on the guaiacol oxidation, however the baseline concentration appears to be the preferred concentration of substrate. III. As the temperature increases, the results show a steady increase, a peak, and a steady decrease in the rate of reaction until the peroxidase becomes inactive. Once the enzyme reaches its optimum temperature, which appears to be 22 degrees, the rate of oxidation will decline afterwards. IV. Varying pH produces similar effect to varying temperatures, except that the optimum pH occurs at around 6.3 on the pH scale. V. Peroxidase is important because it converts H2O2 to H2O. The H2O2 was produced by oxygen metabolism and must be removed because it is highly toxic.Turnips would most likely prefer conditions in which the soil has a slightly acidic pH and a temperature near that of a normal room.