Introduction
Enzymes are catalysts that speed up the rate of biochemical reactions that take place within the cells of organisms, hence they are called biological catalysts (Berg et al., 2012b; H Bull, 2002). They speed up the reactions, by providing an alternative route for the reactions to take place that has a lower activation energy. Enzyme help to increase the rate at which the equilibrium is reached and do not affect the equilibrium constant (Sauro, 2011).
Simple enzyme catalysis can explained as substrates bind to a special cite called the active site on the enzyme and broken down into products. Specificity of the enzyme arises from this, only certain and specific substrates can bind to the active site, by forming weak bonds such as hydrogen bonds with the amino acids forming the active site, and bring about catalysis. Therefore it can be said that one enzyme usually catalyses one reaction (Berg et al., 2012b).
Any factors that can affect the structure and shape of the enzyme, especially the active site, will influence the enzyme activity and its ability to catalyse the substrates. Examples of these factors are temperature, pH and the presence of inhibitors. Also substrate concentration can influence the enzyme activity.
Increasing substrate concentration will increase the rate of the reaction until the enzyme become saturates. After this point, adding more substrate will have no effect on the rate.
Vmax is the maximum rate at which the enzyme can catalyse substrate into products. It is said that at Vmax most of the enzymes exist as enzyme-substrate (ES) complex, where most of the active sites are occupied with substrates. At Vmax, the rate of the reaction is independent of the substrate concentration (Anon 2014; Nelson et at., 2013; Watson 2014). Km is the concentration of substrate at half Vmax and is the “Michaelis-Menten constant”. Km is a good indicator of the affinity of an enzyme to the enzyme. From Michaelis-Menten plot the affinity of the enzyme can be predicted. Lower value of Km means the enzyme has higher affinity for the substrate and vice versa (Berg et al., 2012b; Watson, 2014a).
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Inhibitors are molecules and ions (both “physiological and non-physiological compounds”) that will lower the enzyme activity. There are three types of inhibitors; competitive, non-competitive and uncompetitive inhibitors. Inhibitors do not go under catalysis. Competitive inhibitors often resemble the shape of the substrate and therefore they bind to the active site, preventing the substrate from binding, hence lowering the enzyme activity. However, non-competitive inhibitors bind to a separate site on the enzyme. The substrate can still bind to the active site, but catalysis of the substrate would not take place. Uncompetitive inhibitors have irreversible effects where they usually change the enzyme structure. Therefore the substrate cannot bind to the enzyme. Michaelis-Menten plot can used to identify the type of inhibition. The graph below shows how:
Increasing the temperature will increase the rate of reaction until the optimum temperature. This is due the more kinetic energy is gained by the molecules and they start to move faster, leading to more successful collision. At very high temperatures the enzymes become denatures leading to the inactivation of the enzyme followed by the denaturation which results in the drop the rate of the reaction. (Anon, 2014b; Watson, 2014b).
Enzyme operate within small range of pH. Any small deviation from the optimum range, would decrease the rate of the enzyme catalysed reaction (Anon, 2014b). This produces a ‘bell-shaped’ curve. At very low pH and extremely high pH, the enzymes become denatured (Watson, 2014b).
Therefore the overall aim of this investigation is to see effect of substrate concentration, presence of inhibitors, temperature and pH, on the activity of enzyme, acid phosphatase. Enzyme acid phosphatase is found in many organisms, species and plants. In humans they are found in liver, spleen, bone marrow, plasma of the blood and other places. The pH is different at each place and therefore acid phosphatase will work well at different pH optimum. But as the name suggests, acid phosphatase works best under acidic conditions. This enzyme has optimum pH range between 4-6 and optimum temperature range between 37-50°c (Anon, undated a; Anon, undated b; Anon, undated c; Anon, undated d; D M Mobley, 1984).
http://www.mikeblaber.org/oldwine/BCH4053/Lecture25/Lecture25.htm
http://www.sfu.ca/bisc/bisc-429/enzymeassay.html
http://calzyme.com/commerce/catalog/spcategory.jsp?category_id=1008
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1236033/
http://www.sfu.ca/bisc/bisc-429/enzymeassay.html
References
Anon, (2014a).Vmax – definition from Biology-Online.org. [online] Available at: http://www.biology-online.org/dictionary/Vmax [Accessed 23 Nov. 2014].
Anon. (2014b).Chemistry for Biologists: Enzymes. [online] Rsc.org. Available at: http://www.rsc.org/Education/Teachers/Resources/cfb/enzymes.htm [Accessed 23 Nov. 2014].
Anon. (undated a).Acid Phosphatase – Enzyme assay. [online] Sfu.ca. Available at: http://www.sfu.ca/bisc/bisc-429/enzymeassay.html [Accessed 24 Nov. 2014].
Anon. (undated b).acid phosphatase. [online] TheFreeDictionary.com. Available at: http://medical-dictionary.thefreedictionary.com/acid+phosphatase [Accessed 24 Nov. 2014].
Anon. (undated c).Calzyme -Manufacturers of Enzymes , Proteins , Coenzymes , Substrates and Related Biochemicals. [online] Calzyme.com. Available at: http://calzyme.com/commerce/catalog/spcategory.jsp?category_id=1008 [Accessed 24 Nov. 2014].
Anon. (undated d).Phosphatase, Acid from wheat grem. [online] Sigmaaldrich.com. Available at: http://www.sigmaaldrich.com/catalog/product/sigma/p3627?lang=en®ion=GB [Accessed 24 Nov. 2014].
Berg, J., Tymoczko, J. and Stryer, L. (2012a).Protein Composition and Structure. Biochemistry. 7th ed. New York: W.H. Freeman, pp.25-66.
Berg, J., Tymoczko, J. and Stryer, L. (2012b). Enzymes: Basic concepts and Kinetics.Biochemistry. 7th ed. New York: W.H. Freeman, pp.227-260.
D M Mobley, J. (1984). Effect of pH, temperature and media on acid and alkaline phosphatase activity in “clinical” and “nonclinical” isolates of Bordetella bronchiseptica.Canadian Journal of Comparative Medicine, [online] 48(2), p.175. Available at: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1236033/ [Accessed 24 Nov. 2014].
Figure 2. Enzyme: Structure and Function. (2012). [Sketch]. Available at: http://schoolworkhelper.net/enzymes-structure-and-function.html [Accessed 22 Nov. 2014].
H Bull, P. (2002). Acid phosphatases.Molecular Pathology, [online] 55(2), pp.65-72. Available at: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1187150/ [Accessed 22 Nov. 2014].
Nelson, D. and Cox, M. (2013).LEHNINGER PRICIPLES OF BIOCHEMISTRY. 6th ed. London: Macmillan Higher Education, pp.189-242.
Sauro, H. (2011).Enzyme kinetics for systems biology. Lexington, KY: Ambrosius Publishing, pp.53-57.
Watson, D. (2014a). LSC-10034 Nature’s Tools – Proteins and Enzymes. Lecture [on 4 Nov. 2014].
Watson, D. (2014b). LSC-10034 Nature’s Tools – Proteins and Enzymes. Lecture [on 11 Nov. 2014].
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