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The activity of the enzyme Tyrosinase

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The activity of the enzyme Tyrosinase Introduction: In this assignment I will be looking at how two factors affect the activity of the enzyme tyrosinase. These factors include the concentration of the substrate and the concentration of the enzyme. Other factors that also have an affect on the rate of a reaction include temperature and pH where enzymes have an optimal pH, which they work at. Biological processes are controlled by the action of enzymes, which are biological catalysts. Enzymes act on specific substrates and their active site shape is complementary to their shape of the substrate. The enzyme and substrate form an enzyme-substrate complex. An enzyme substrate can be only formed if the enzyme's active site and the substrate have complementary shapes. The enzyme is said to have a three dimensional shape. This said to be complementary to that of the substrate and binding the substrate to the enzymes active site makes the substrate react more quickly. The model of the enzyme action is the lock and key hypothesis only one substrate the (key) will fit in the active site (the lock). It is know thought that the active site changes shape so that the enzyme moulds itself around the substrate. The diagram below shows this mechanism, A shows the lock and key hypothesis; the substrate and active site are complementary in terms of shape and chemical charge. B shows the induced fit hypothesis as the substrate combines with the active site; the enzyme molecule alters its shape and moulds itself around the substrate. Reactions only proceed if the reacting substance collides with sufficient energy to overcome the energy barrier there would be a reaction. ...read more.


> You then take a 1-20 ul pipette and set it at 20ul. Take up 20ul of tyrosinase enzyme and place in the same cuvette. Soon as you do these give the cuvette a stir using the stirrer and place it in the spectrophotometer as mentioned above. The enzyme is placed at the end to the cuvette because it starts of the reaction at this point. Make sure that you have set the spectrophotometer at 475nm and start the calibration by pressing the zero button. You would then be required to record the changes in absorbance after 5 minutes and 7 minutes. You would record you're results as in table 2. You are then required to carry out the same procedures using appropriate pipettes to maintain accuracy and precision using the concentrations in table 1 for cuvette numbers 2, 3 4 and 5. Table 2: Substrate concentrations Time (Min) Concentration volumes used in microlites Cuvette 1 2 3 4 5 3 (min) 5 (min) Optical density (mg /2 min) N.B: The numbers 1-5 indicate the cuvettes with different concentrations of the substrate L- tyrosinine (these were calculated and are shown in the results table 5). The change in optical density is determined at each substrate concentration by subtracting the optical density at 5 minutes minus the optical density at 3 minutes: This is shown in the equation below: OD 5min - OD3min = OD/2min Procedure: (Enzyme concentration): In this part of the experiment you would be required to carry out the same procedures as in the substrate concentrations using the micropipettes and setting the spectrophotometer at 475nm, and recording you're results after 3 minutes and 5 minutes using the changes in absorbance. ...read more.


Therefore if the concentration of substrate is increased and the rate concentration of enzyme the reaction would proceed as normal as more active sites become available for the enzyme substrate complexes to be formed. Graph B on page 10 shows a linear portion of the plot; increase in enzyme concentration keeping the concentration the substrate L tyrosine the same keeps the reaction on going as the properties of enzymes reflect the fact they are proteins. The rates in which enzymes catalyse reactions are often called its velocity. Enzymes velocities are normally reported at times zero since at this point the rate is at its fastest but at this point no product is present in this case L Dopa quinine. This is because the concentration of the substrate L tyrosine is greatest before any substrate has been transformed to product because the enzymes maybe subject with the reversible reaction as the products will reverse the reversible reaction. Enzymes have a precise and delicate tertiary structure anything that disrupts this structure i.e. the rate of formation of enzyme-substrate complex (e.g. blocking the active site) will interfere with the enzyme activity. The graph shows a positive correlation between the substrate and enzyme and suggests that the rate is on going. In conclusion my prediction was correct; the rate of reaction does increase as the substrate concentration increases. The reaction did increase up until the point where the enzymes are working at its fastest i.e. when all the active sites are filled all the time i.e. when saturation took place. On the other hand for the enzyme Tyrosinase re enzyme has a particular active site that have an exact shape to the substrate L tyrosine to form a substrate complex. As the substrate concentration was increased with the enzyme the rate of reaction also increased. ...read more.

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