Determining The Rate Of Reaction Of Enzyme At Different Temperature

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Enzyme was introduced by Kiihne in 1878, even though the first observation of enzyme activity in a test tube was done by Payen and Persoz in 1833. Enzymes are specialized proteins that make cellular work possible in all cells by helping chemical reaction to occur. these chemical reaction speed up the chemical activity by increasing the reaction rate, or rate at which a reaction occurs, measured in terms of reactant used or product formed per unit time. Enzymes are globular proteins with depressions on their surfaces; these depressions are called active site, where the substrate fit and where the catalysts occur. Substrate fit closely to the active sites because enzymes can adjust their shapes slightly to accommodate the substrate. This process involves three- dimensional shape, of enzymes when the substrate binds to it. The change in shape of the active site to accommodate the substrate is called induced fit, and this process brings the functional group on the enzymes into the proper orientation with the substrate to catalyze the reaction.

Various substances can inhibit the action of the enzymes which can cause the enzyme to shut down its activity. Non inhibition is and inhibitor molecules that binds at a site know as allosteric site which prevents the three dimensional structure of an enzyme from binding to the active site. The competitive inhibition involves a chemical compounds that bind to the active site of the enzymes and inhibit enzymatic reactions. The compound competes with the true substrate for the access to the active site. This completion is possible because competitive inhibitors are very similar in shape and structure to the enzymes' substrate. Allosteric inhibition has two active sites, one for a substrate and one for an inhibitor. When the inhibitor binds to the active site, the enzyme undergoes a change, the active site for the substrate is changed which causes the enzyme not to catalyze the reaction. Inhibitors cause the allosteric enzyme to take up the inactive shape, where activators support the active shape. Another type of inhibition is called feedback inhibition; this is a type of non-competitive inhibition in which the end product of the pathway binds at an allosteric site on the first enzyme of the pathway. In cells, enzyme inhibition is usually reversible, that is because the inhibitor is not permanently bound to the enzymes. Inhibition of enzymes can also be irreversible.

In competitive inhibition the inhibitor is similar in structure to the substrate and it binds to the enzyme at the active site. In feedback inhibition, the inhibitor binds to the enzyme at a site away from the active site and acts by changing the shape of the enzyme in a way so that it is incapable of catalyzing the reaction. Feedback inhibition is a natural part of the process by which an organism regulates the chemical reactions that take place in its cells.

Like most chemical reactions, the rate of an enzyme-catalyzed reaction increases as the temperature is increased. So generally, as temperature increases so does the rate of reaction, however high temperature can cause denaturation of the enzyme. Enzyme activity can also be affected by pH, in the same way that every enzyme has a critical temperature, so each enzyme also has a critical pH at which it works best. In the case of catalase, the most favorable pH is approximately pH 7.0. The catalase works best at a neutral pH, if the solution is too acidic, or too basic the catalase is inactive and no longer functions as an enzyme. Catalase is a common enzyme found in a living organism it can found in the liver. Its functions include catalyzing the decomposition of hydrogen peroxide to water and oxygen. Catalase is necessary because Hydrogen peroxide is a harmful by-product of many normal metabolic processes, to prevent damage; catalase is frequently used by cells to rapidly catalyze the decomposition of hydrogen peroxide into less reactive gaseous oxygen and water molecules.

Observation Chart

Test tube/degree Celsius

Height of bubbles(mm) / Reaction Time 30sec.



















Figure 1.0

Figure 2.0


The enzymes activity increase as temperature increases but only up to a maximum point (35o-42o). If the temperature increases beyond this point, the enzymes activity decreases because the enzymes have been denaturized. When this happens, its shape changes and it can no longer bind to its substrate.


Take 4-5 test tubes and fill them with 4drops of hydrogen peroxide (H2O2) and to do this you will need a nose dropper. You also need a test tube fill with live in it so you can take another nose drop to put the liver in test tube to react with hydrogen peroxide, put only 2-3 drops of liver in hydrogen peroxide. You also need a beaker and a hot plate to test the enzyme at different temperature. Make sure that all the test tube the liver one and the hydrogen peroxides one are in the beaker when you are heating the beaker up because you everything to be at the same temperature while doing the experiment. Do not mix the liver and the hydrogen peroxide with the liver before heating it up because it will react immediately and you want to test it at different temperature. Use a thermometer to calculate the temperature and when you see the temperature you wanted take the beaker off the hotplate because if don't take off the beaker it will increase the temperature. Then use a nose dropper to take the liver out of the test tube and put 3 drops of liver in hydrogen peroxide and make sure that everything is the beaker. Calculate the time for 30 seconds and measure the height of the bubbles with your ruler.


To do this lab you will need 5 test tubes, a beaker that can easily fit 5 test tubes in it, a hot plate 2 nose droppers, hydrogen peroxide (H2O2), and liver as an enzyme, and a thermometer to calculate the temperature.


The purpose of the lab is to determine the temperature affect on catalase activity and at what temperature is enzyme at its maximum point and at what temperature it drops rapidly.


Temperature can affect the rate of an enzyme reaction as they increase or decrease. Molecules collide much faster as the temperature increases causing increases in the rate of a reaction. Temperature increase the collision rate which makes the substrate collide with the active site of the enzyme, therefore increasing the rate of an enzyme-catalyzed reaction. Above the critical point, activity begins to decline because the enzyme begins to denature the rate of chemical reactions therefore increasing the temperature above the critical point will then decreases as enzymes denature. Most human enzymes functions best at 35 -40 degree Celsius. Below this temperature range, enzymes are less flexible and therefore less able to provide and induced fit to substrate. Above this range bonds become weaker and less able to hold peptide chains in the enzyme in the proper orientation. But as you can look at the observation table the enzyme worked 10 degrees above that temperature and then denatured which bring to a conclusion of an error or contamination in either test tube, liver or the substrate which was H2O2.


Determining the effect of temperature on catalase activity by increasing the temperature and to test the rate of the reaction was part of the lab where as the temperature increased so did the reaction as expected, but the reaction did go above the critical point before getting denaturized. To sum up, the result that was gained after the experiment was not precise to the hypothesis.