The effects of temperature, PH value, substrate & enzyme concentration and those of inhibitors and cofactors are of particular biological interest and can be summarized as follows:-

        

The induced fit action of an enzyme can be explained further in terms of its effect on the activation energy of the reaction it controls. In any chemical reaction, the molecules involved must acquire a certain amount of energy from their surroundings before chemical changes are possible. This energy is called activation energy. For reactions which occur spontaneously at normal temperatures sufficient thermal energy is always available, but in many other cases, the activation energy represents a “barrier” which slows down or prevents the reaction – referred to the figure below –

                                                                                                                                                                                                                                                                     

This barrier can be overcome by increasing the temperature & pressure to speed up the movements of the reacting molecules, thereby increasing their kinetic energy & making collisions more likely.

The reaction is also speeded up if a suitable enzyme or other catalyst is available.

By changing the shapes of their substrates, enzyme molecules reduce the energy needed for the formation of reaction intermediates. In other words, they reduce the activation energy for the reaction, allowing it to take place at ordinary temperatures and pressure.

          Enzyme controlled reactions have a number of important characteristics related to the mechanisms of enzyme action described above, and to the fact that all enzymes are proteins. The effects of temperature, PH value, substrate & enzyme concentration and those of inhibitors and cofactors are of particular biological interest and can be summarized as follows:-

          The relationship between temperature and the reaction rate for a typical enzyme is illustrated in the figure. 

The initial increase in reaction rate with rising temperature is the expected result for any chemical reaction because the increased heat energy raises the kinetic energy of the reacting molecules, leading to more frequent collisions. In this case, more enzyme substrate complexes are formed per unit time, with a corresponding increase in catalysis and in the number of product molecules.

        

With many reactions involving an inorganic catalyst, this increase would continue indefinitely, but in an enzyme controlled reaction, an optimum temperature is soon reached corresponding to the maximum reaction rate. Above the optimum temperature, the reaction rate falls off sharply. This is because enzyme molecules like all proteins, owe their shape to weak attractive forces like hydrogen bonds, these bonds became unstable at higher temperatures, causing the enzyme to become denatured. The active centre loses its correct configuration & fails to fit the substrate so that the enzyme no longer functions as a catalyst.                                                                                                        

        

More enzymes have optimum temperatures between 40 – 50 °C, but there are some specialized types which function best either above or below this range. For example certain kinds of bacteria survive in hot springs above 85°C and require particularly stable enzymes. At the other extreme, the ice fish of Antarctic waters has enzymes which function efficiently at -2°C.  

          Most enzymes have an optimum pH close to pH 7, which is the normal intracellular pH. This is illustrated in the figure. 

Enzymes which work extra cellularly can have very different pH requirements.

A notable example is the enzyme pepsin which is found in the stomach and works best in highly acidic conditions in the range pH 1 – 2

 pH changes away from the optimum can affect enzyme activity adversely in either of two ways. In cases where the binding or catalytic sites within the active centre take the form of charged ions, some values of pH are inhibitory because they cause these ions to re associate.  The uncharged groups formed as a result can no longer interact with the substrate & so catalytic activity is lost. A second possibility is that the enzyme molecule can change shape and become denatured: this is more likely to happen at extreme values of pH which tend to weaken the forces holding the enzyme molecule together.

          In my course work, I am investigating the effect of temperature on the activity

 of enzymes.

 : Test tubes, Beakers, Connecting tube, Stopper, container, Bunzen burner,  

               knife, Measuring cylinder, Syringe, Thermometer

 : Hydrogen peroxide, Catalase, Water

 

         In my experiment, I will change the temperature values from 10°C to 70°C.

 

         I want to observe the amount of oxygen released from the breaking of hydrogen peroxide collected in the measuring cylinder

 

          Using same concentration and volume of hydrogen peroxide in all experiments and using same number& length of potato rods.

: It is carried out in order to obtain the most suitable range of temperature for the enzyme catalase found in the potato tissues.

 

• Fill a big container with water.
• Immerse a measuring cylinder in the water container &

      support it using a tube holder so as not to sink down.

• Put some potato chips in a test tube & put the test tube in a

                small beaker.

• Connect the measuring cylinder with the test tube using a

      connecting tube and pass it through a stopper.

• Fill the beaker with water & put the test tube in it & use a

      thermometer to detect different temperatures used in the

      reactions.

• Add 5 cm³ of hydrogen peroxide to the test tube & cover it   quickly with the stopper to prevent oxygen loss.
• Repeat the experiment several times and take the average for accurate results.

   

      I repeated the experiment 3 times in my course work using different values of

      temperature 10°C 20°C 30°C 40°C 50°C 60°C 70°C 80°C

      Safety precaution: There must be a Fire extinguisher; we must wear White Coat, Gloves and Goggles for protection from any splashes

Precaution for accurate results: First we must repeat the experiment several times to get accurate results, Use equal no. of pieces of potato in every experiment and equal lengths , Wash the test tubes before using it.

:

       Before doing the experiment I predict depending on what I studied that on using temperature 10°C the enzyme would be inactive and wont give any results but on doubling the temperature the enzyme would be active , on temperature 40°C it might be the nearest to optimum temperature for the enzyme to work.

After applying the steps mentioned above the following results were observed:

• In my experiment I used a suitable extent, I replicated the experiment several times therefore I can draw a conclusion.

• I used a suitable range from 10°C to 80 °C to make sure that I have enough evidence in my experiment and I think that I covered a good range.

• took the average of my of my results to make sure its accurate and I also used some equipments like the thermometer, stopper, measuring cylinder & syringe for accuracy.

The results were represented in the following graph:

: First, from 10°C to 40°C the rate of reaction was going faster & faster on increasing the temperature. Secondly, from 40°C to 80°C the rate of reaction was decreasing on increasing the temperature. It was obvious that the optimum temperature was nearly    40°C as it showed the highest volume of oxygen released.

: The first part from 10°C to 40°C the volume of oxygen was increasing because the rate of reaction was going faster as the enzymes gained energy so they reacted faster but when it reached over 40°C some of the enzymes got denatured on increasing the temperature

: I found that on increasing the temperature by 10°C at a time the rate of reaction is doubled but this process has a limit which is the optimum temperature of the enzyme to work on as on exceeding that temperature the enzymes start to be denatured on going higher.

I replicated my experiment several times through my coursework and it was obvious that the conclusion supported the prediction depending on my studies.

       On testing a high temperature we need heat the beaker of water on bunzen burner but after getting the wanted temperature and removing the beaker from over the burner the temperature may decrease by time so we must prepare a syringe full of hot water so as the temperature goes down we can add water from the syringe to maintain constant temperature needed for fair comparison.

We could use sensitive balance to measure the mass of the potato discs used in the experiments so we can have more accurate results needed for fair comparison.

Using suitable length of the connecting tube so as not to have a lot of air inside it which would affect the accuracy of the experiment & also a suitable size of a measuring cylinder so as we can see the small differences

I think that further investigation is needed to use wider range of temperatures and more accurate equipments to obtain more accurate results.

:

      It is obvious that there were sum errors in my experiments as on using temperature 20°C  as more oxygen was released more than predicted & I think that was because of the air inside the tube as heated and expanded & made more air released.

      I think that some oxygen was lost in the time between putting the hydrogen peroxide & closing the stopper over the test tube. But I think that I did my best to have the most accurate results I could obtain.