Effect of Temperature on an Enzyme Controlled Reaction

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To investigate the effect of temperature on an enzyme controlled reaction

Introduction and planning

For the investigation of enzymes, I am going to conduct an experiment to see how temperature can affect the rate of reaction of enzymes by testing it with starch. The enzyme that we are going to use is called amylase. We are going to test this enzyme with starch. By mixing amylase and starch solutions together under different temperature conditions, we can record the rate of reaction by taking a sample out and test it with iodine solution to see if there is any remaining starch present. We have to use the enzyme amylase because enzymes will only work on a specific substrate i.e. amylase will work on starch because of its special shape of active site. This is known as the ‘enzymes specificity'.

The enzyme amylase is used for hydrolysing starch and glycogen to form glucose and maltose. This enzyme is found in human saliva for the use of breaking down starch in food, enabling the body to absorb and produce ATP energy.

Enzymes are in all living organisms, they are proteins made up of polypeptide chains (which are made up of many amino acids) with irregular components which give it a globular shape. This makes it a dense, small, compacted molecule that can move around very easily.

For the enzyme to work, it must collide with a substrate. If they collide at the right place, the substrate will then ‘fit' into the active site of the enzyme forming enzyme-substrate complex; fitting into the active site puts a strain on bonds in the substrate, so the substrate molecule breaks up more easily. In order for any reaction to occur, there must be energy to allow it to happen; this is called the activation energy. As shown below.

This is a general graph that shows how activation energy works. The top dotted line to the time line is the activation energy needed for the reaction without enzymes; and the second dotted line to the time line is the energy needed to start a reaction with enzymes. This clearly shows that the differences between using an enzyme to start the reaction and not using it. The y axis represents two different things on this graph; the positive represents the used energy to start the reaction, and the negative half is showing the energy released for the reaction. Overall, the reaction with the enzymes can work faster then the other one without, but they still reach the same energy out-put at the same time forming same the products, also with the help of enzymes, the energy needed to start the reaction reduces compared with the energy needed without the enzyme. There are many factors can affect the rate of reaction in enzymes: •Temperature

•Concentration of enzymes
•Concentration of substrate

This factor has a big influence on enzymes' activity, because like any other chemical reaction, heat is needed to give the molecules more energy to move around – kinetic energy, so the molecules will move faster and therefore increase the chance of collision. The following graph shows the general reaction rate of the enzymes against the temperature.

As the temperature increases, the reaction of enzymes also increases due to more kinetic energy; more vibrations, resulting an increased rate of collision with the substrate. But as it goes above the maximum temperature (optimum temperature), it starts to decrease rapidly. This is because the high temperature/ the high kinetic energy breaks the bonds that hold the enzyme's tertiary structure together which change the shape of the active site and will not react with the substrate anymore – denatured. Denaturation is often irreversible.

There is also an optimum pH value where the enzymes work most efficiently. Most enzymes work best around pH 7, which is neutral. pH is a measure of hydrogen ions in a solution, if it is too acidic, the enzymes will become denatured, if the enzymes are...
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