To investigate how different factors affect the rate of breakdown of sucrose by the enzyme sucrase.

pH Value

There is an optimum pH value for all enzymes where the rate of reaction is at it's quickest. If the pH value moves too far either way the enzyme will become denatured. Most enzymes optimum pH value is between pH 5 and 9 however most catalyse most efficiently pH 7. Arogant of denaturing the enzyme, a change in pH alters the ionisation of the amino acid side chains at the aqctive site.

Concentration of enzyme and substrate

As the concentrations of enzyme and substrate increase as does the chance of particle collision between the two. Obviously this speeds up the rate of reaction however the rate become constant as the enzymes works at it's stop speed.

Temperature

I have chosen tempertaure to be my variable factor in my investigation. I have chosen this as varying the temperature is easy compared with others. This is time efficient.

Increasing the temperature of the substrate means the substrate will gain kinetic energy as the kinetic theory states.

Heat is absorbed by particles, which is converted into kinetic energy, causing them to move more rapidly.

Obviously if the particles are moving far more rapidly due to absorbed kinetic energy this will increase the chacnce of molecular collisions. The greater the amount of molecular collisions the greater amount of enzyme- substrate complexes will be formed. This will obviously increase the rate of the reaction.

However if too much heat is absorbed by the molecules they will vibrate greatly and become too violent meaning their bonds with the enzymes will break. This will cause the collapse of the tertiary structure of the enzyme. When this happens the enzyme become denatured.

There is a specific temperature of all enzymes where the enzymes gain their maximum potential of heat energy but do not lose their tertiary structure. This is called their optimum temperature. This means the enzyme may speed up the rate of the reaction to its greatest. The optimum temperature varies from enzyme to enzyme and when this is exceeded the enzyme starts to become denatured.

In this experiment I hope to obtain results on how long it takes for the substrate to be catalysed by the enzyme to form glucose and fructose. To determine when glucose is formed we will use clinistix to inform us. When the tip of the clinistix (pink) turns blue we will know glucose is present. This is when we will stop timing. To obtain the rate of the reaction from this time I will simply take the recipricol of it.

Method

To begin the experiment the following list of apparatus must be assembled as shown in the diagram below.

* Water bath

* Test tube rack

* Test tubes

* Thermometer

* Measuring cylinder

* Stopwatch

* Clinistix

* Distilled water

* 10% sucrose solution

* 5% enzyme solution

Diagram of appartus

* Firstly we will measure 5cm of 10% of sucrose solution with a measuring cylinder and pour it into a test tube.

* We will then measure 5cm of 5% sucrase solution into a measuring cylinder and also put it into a test tube.

* We will then place the test tubes with sucrose and sucrase into the water bath which is heated appropiately to a certain temperature. This will heat the solution. Let the sucrose acclimatise for 5 minutes.

* Check the temperature of the sucrose with the thermometer.

* We then add the clinistix to the sucrose solution.

* We mix the two solutions together.

* Add this same point we start the stopwatch in order to stop it when the clnistix turns blue, thus glucose being present.

* When the clinistix does turn blue we stop the clock stop and record the results.

* We repeat this procedure 3 times for each temperature to get an average and we carry this out for 10, 20, 30, 35, 40, 45 and 50 degrees celsius.

* Record the results in a table.

Precautions

We must allow the sucrose to acclimatise to it's accordant temperature in the water bath before adding the sucrase enzyme. For each experiment stop the stopwatch only after the clinistix turns to a similar, certain shade of blue. We must also remember to wash all the equipment with distilled water after each experiment to remove any residue that may affect the next set of results.

In order to make sure it is a fair test we must make sure we keep all other variables exactly the same. We may keep the pH values the same by adding buffer solution. We must also only use the same volume and concentration of solution each time and we must only vary the temperature.

We take a greater number of readings around the enzymes temperature (35, 40, 45 degrees celsius) for greater accuracy. We know the optimum temperature for sucrase is 40 C. (Acknowledgment : Advanced Human Biology, J. Simpkins and J.I. Williams)

Hypothesis

For each and every enzyme reaction the temperature coefficient law (Q10) is vital for predicting rates of reactions.

Q10 = Rate of reaction at T + 10 C

Rate of reaction at T

(Acknowledgment : Advanced Human Biology, J. Simpkins and J. I. Williams)

This equation expresses the effect of a 10 C on the rate of reaction. According to this equation if I were to use the time taken as the rate of reaction it would half every 10 C temperature rise, however as I am using the reciprocol it will double.

With this in mind I am finally able to predict that the rate of reaction will increase with the temperature and as the temperature increases by 10 C the rate will double. This is until the temperature exceeds the optimum temperature. I predict that the rate of reaction is proportional to temperature.