The fit together forming an enzyme- substrate complex
Chemical bond is broken- the enzyme remains unchanged
Catalase
“Catalase is one of the most potent catalysts known. The reactions it catalyses are crucial to life. Catalase catalyses conversion of Hydrogen Peroxide (H202), a powerful and potentially harmful oxidising agent, to water and Oxygen. Catalase also uses Hydrogen Peroxide to oxidise toxins including Phenols, Phormic Acid, Formaldehyde and Alcohols.”
Factors Effecting the Reaction of Hydrogen Peroxide → Water + Oxygen
The main factors that would effect this reaction are:
- Temperature of the Hydrogen Peroxide
- The pH of the Hydrogen Peroxide
- Concentration of the catalase in the Hydrogen Peroxide
I am now going to talk about these factors individually explaining how the effect the reaction of Hydrogen Peroxide with water and Oxygen.
Temperature
Enzymes have certain temperatures that they work the most efficiently at, ‘optimum temperature’. When the enzyme is at its optimum temperature it works at its best, this would be when the reaction works the best. When the solution reaches a certain temperature the enzyme, catalase will become denatured and will not work. All chemical reactions speed up as the temperature is raised. This is because as the temperature increases, more molecules have the kinetic energy to undergo the reaction. If the temperature is increased over the optimum temperature the enzyme becomes denatured. This is when the kinetic energy of the enzyme and water molecules is so great that the structure of the enzyme molecules start to be disrupted.
To do this experiment a range of 200C- 700C would probably be sufficient, as most enzymes denature at around 400C - 500C. Approximately 6 different temperatures should be used to ensure a good range.
pH
Just as enzymes have an optimum temperature they also have an optimum pH. When the enzyme is at its optimum pH it works at its best, this would be when the reaction works the best As the pH of an enzyme is lowered it tends to gain H+ ions, as the pH is risen it tend to lose H+ ions. Both the gaining and losing of H+ electrons, this effects the enzyme and the shape is disrupted, the enzyme is denatured. Many enzymes have an optimum pH of neutral and are denatures at high and low pH. To test for the difference that pH has in an enzyme controlled reaction a range of pH’s are needed. This is good pH range to use within a school laboratory;
Hydrochloric Acid (pH 1, strong acid)
Lemon juice (pH 4, weak acid)
Distilled water (pH 7, neutral)
Sodium Bicarbonate (pH 10-11, weak alkali)
Sodium Hydroxide (pH 14, strong alkali)
Concentration of Catalase
The amount of catalase should alter how fast the reaction is taking place. The reaction should speed up when the concentration of the catalase increases. This is because there is more of the enzyme to take part in the reaction. If there was a very low concentration of catalase the reaction would take place, but just slower than at higher concentrations.
Plan
The idea of this experiment is to study the enzyme catalase, which accelerates the breakdown of hydrogen peroxide into water and oxygen. To do this I will alter one variable, this will be pH. I aim to find the effect that different pH’s have on the efficiency of the enzyme.
The way that I am going to measure how well the enzyme work in different pH, I am going to collect the oxygen gas that comes from the experiment. I cam do this because only when the catalase has broken down the hydrogen peroxide into water and oxygen will the gas be collectable.
Equipment
There are various types of equipment that you can use to collect the oxygen that will come from this experiment. These are the various ways and why or why not they are the best/most accurate way of measuring the oxygen:
- Counting the bubbles that come from the experiment. This is a very simple way of doing the experiment, but the problem with this is that it is not qualitative, this makes it less accurate. Bubbles that come off from the experiment may be different sizes and therefore this would not be an appropriate method to use.
- Collecting the gas in a ages syringe. This is a very good method, as non-of the gas can escape. The problem with this technique is that the syringes sometimes get stuck and therefore do not record the measurement accurately enough.
- The other two methods are collecting the gas in a measuring cylinder or using an inverted burette. These are both very good ways of measuring the gas. They are both quantitative and therefore are both accurate.
The method that I am going to chose is collecting the gas in a measuring cylinder.
Equipment list:
- Boiling tube
- Bung
- Delivery tube
- Test tube holder
-
Measuring cylinder (100cm3)
- Beehive stand
- Hydrogen Peroxide
- Catalase solution (celery)
- Water
- Distilled water
- Hydrochloric acid
- Lemon juice
- Sodium bicarbonate
- Sodium hydroxide
- Stop watch
Diagram
Measurements
In this experiment you need to measure the amount of gas that is given off from the experiment in regular intervals of 2 minutes for each of the different pH’s. To make the test as reliable as possible 5 readings are sufficient. From the result that you get from the experiment it is possible to work out the gas per minute given off from the experiment. Another way of measuring how fast the hydrogen peroxide is being broken down is to measure in seconds how long it takes for 20 cm3 of gas to be produced. I am not choosing this method I am choosing to do how much gas is produced each minute.
Fair Test
To make this experiment a fair test I will need to keep all the variables the same except the one that I am investigating, pH. I will also need to repeat the test 4 times to ensure that there is a high level of accuracy and possible mistakes are spotted.
Health and Safety
The acids and alkalis that are used are not very dangerous, but if they come into contact with skin, eyes etc. they should be washed with water. Goggles and lab coats should be worn at all times, and hair should be tied back. All bags should be taken from the laboratory of put in a suitable place where they will not cause an accident.
Recording the results
To record the results I will use a table like this, one for each of the pH:
Method
Take 10cm3 of hydrogen peroxide with 5 cm3 of distilled water, and place in a boiling tube. Set up the rest of the apparatus as shown in the diagram. Fill the measuring cylinder with water and place upside down in the water bath. Take the measurement of water from the measuring cylinder, then place 5cm3 of catalase in the boiling tube with the hydrogen peroxide. Take measurement every 2 minutes and record them on the table. After 10 minutes repeat the experiment again 5 times. Repeat this again with all of the different pH’s (hydrochloric acid, lime water, sodium bicarbonate and sodium hydroxide).
