In order to convert substrate, Hydrogen Peroxide, into product, oxygen and water, the . Increasing the temperature will increase the number of collisions of enzyme and substrate.
The internal energy of the molecules may include vibration energy and rotational energy of the molecules, the energy involved in chemical bonding of the molecules. Some of this heat may be converted into chemical potential energy. If this chemical potential energy increase is great enough some of the that determine the may be broken. Thus too much heat can cause the rate of a reaction to decrease because the enzyme becomes denatured and inactive.
Enzymes act by binding substrates, forming a complex. The complex stresses chemical bonds forming a transition state. This makes the substrate more reactive. Energy is needed to form this state and the enzyme provides it. The enzyme's site of attachment and the parts that stress the substrate's bonds is known as the active site.
The rate at which an enzyme works is influenced by several factors including the concentration of substrate, concentration of enzyme, temperature, pH, salt concentration and the presence of inhibitors or activators. Every enzyme has an optimal range for each of these factors. Activity decreases when an enzyme is exposed to conditions that are outside the desired and best, optimal range. In this case, catalase possesses an optimum temperature of 40oC. In general, chemical reactions speed up as the temperature is raised. When the temperature increases, more of the reacting molecules have the kinetic energy required to undergo the reaction. Enzyme catalysed reactions also tend to go faster with increasing temperature until an optimum temperature is reached. Above this value the enzyme molecule is disrupted, or denatured. In denaturation, the globular protein begins to unravel as the bonds holding it together vibrate so rigorously that they break. A denatured protein cannot combine with a substrate.
The tertiary structure of a protein depends on interactions such as hydrogen bonding, between R groups. In globular proteins, the polypeptide chains are tightly folded to form an almost spherical shape. Therefore, temperature affects the three-dimensional structure of all enzymes.
A higher temperature will result in an increase in enzyme activity. As the temperature rises, the movement of enzyme molecules and substrate molecules increases as the atoms are given more kinetic energy to collide successfully, thus increasing the rate. This causes more collisions between enzyme and substrate and the net result is the formation of more product. As the temperature continues to rise beyond a certain point, however, the hydrogen and ionic bonds, which hold the enzyme molecules in shape, are broken. If the molecular structure is disrupted, the enzyme ceases to function as the active site no longer accommodates the substrate. The enzyme is denatured.
At low temperatures, the reaction takes place very slowly as the substrate molecules do not collide frequently with the active site of the enzyme, so an enzyme-substrate complex is not formed. As the temperature rises, more energy has been given to the molecules causing collisions and increased rate of reaction.
Temperature table:
Method:
- Set the apparatus accordingly:
- Place 3 boiled peas in test-tube half-filled with distilled water, in another test tube place 3 unboiled peas in the same way.
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Place these test tubes in the water bath of the required and set temperature, in this case 30oC, for a minimum of 15 minutes to allow the peas to form an equilibrium with the temperature in the water bath.
- After the peas have equalised in temperature, they can be removed from the test-tube and the coat can be removed.
- Crush the peas in the pestle and mortar to increase surface area for the reaction. Then place in the conical flask.
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Get the stopwatch ready and pour 10cm3 of Hydrogen Peroxide into the conical flask and quickly replace the bung. The stopwatch should immediately be started as soon as the substrate is poured in.
- Record the volume of gas collected every 30 secs for a total duration of 5 minutes.
- This method should be repeated 3 times for each temperature.
Apparatus:
- Conical flask
- Pipette
- Gas syringe
- Thermometer
- Water baths
- Ice
- Peas
- Pestle and mortar
- Scalpel
- Distilled water
- Hydrogen Peroxide
- Stopwatch
Safety:
- wash hands after using chemicals
- wear goggles at all time during experiment
Variables:
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The Independent variable will be the temperature, as I will vary it, This could affect the rate of reaction because the higher the temperature then more collisions per second will take place. If the temperature changes it will effect the rate of reaction between the reactants, either by speeding it up if the temperature rises because the molecules move faster and travel a greater distance in a given time and so will be involved in more collisions or by denaturing the enzyme as the enzyme is found in the human body that has an optimum temperature of 400C. Moreover, a very low temperature may cause the enzyme to halt and seize to function. There will be several different temperatures, which will give me a wide range of results, which will be reliable and reproducible.
- The dependent variable will be the time taken for the rate of reaction to take place (i.e the most amount of oxygen gas collected), because it depends upon the temperature.
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The volume of substrate used will stay the same (10 cm3) to ensure a fair test. The amount of enzyme used will also remain constant (3 peas).
- Moreover, there will be no buffer present thus there will be no pH level control present.
Fair test: To ensure a fair test is carried out a thermometer will be placed in the electronically controlled water bath to monitor a constant temperature.
It is important to keep the reactants separate while setting up the apparatus so that the starting time of the reaction will be measured accurately. Lastly, each experiment will be repeated three times to calculate and average result. This will ensure that there are no abnormal results and it will increase accuracy.
Results:
Final table of results (Averages):
Results for the Total Volume of oxygen gas collected (cm3)
Conclusion
In conclusion I think the results did prove my hypothesis that as the temperature increases gets the faster the rate of reaction. However, as catalase is an enzyme found in the human body as well, beyond 40oC the enzyme will be denatured.
The graph shows the effect of temperature on enzyme activity. As the temperature rises, the rate of reaction increases until the temperature reaches a point at which the enzyme begins to denature. The rate drops off steeply as denaturation progresses and becomes complete.
When the temperature is raised, the initial rate of reaction is increased. And the enzyme is instable. Excess heat irreversibly changes the secondary and tertiary structure of the enzyme. This causes its specific shape to be altered along with the position of the amino acids that usually hold the enzyme in its structured shape and the active site. Thus, the enzyme is disabled and cannot accept any substrate molecules, as it has lost its catalytic abilities and functions.
From the graph, fig.1 we can see that it takes longer for the Oxygen gas to be produced when the enzyme is subjected to lower temperatures (00C), producing 16cm3 of oxygen gas in 300 seconds in comparison to the 400C which shows a steep gradient, producing more than that volume of oxygen (17.3cm3) in 120 seconds in a rapid and vigorous reaction. However, when the temperature reaches above the optimum, the rate of reaction decreases to a total of 25.67cm3 of oxygen production (at 500C) to no reaction at 600C, as shown in fig.2.
Fig.2 displays the total volume of oxygen gas collected in the varying temperature conditions.
The graph shows that the closer to the optimum (400C) the temperature is, the faster the rate of oxygen production will be accept after this as the enzyme is denatured.
Evaluation
I believe that the experiment was designed well and the results followed the general trend proving my hypothesis to be correct. However, an anomaly can be detected from fig 1.2 which describes the overall trend of rate or reaction. At 200C the total volume of oxygen gas collected decreases from 20.3cm3 at 100C to 18.8cm3.
This anomaly could be due the results being obtained from different groups, thus difference in equipment use and procedure may have produced this variation. Moreover, this result could be due to the fact that a controlled electronic water-bath was not used for this particular temperature, thus the temperature was not constantly maintained during the course of the reaction.
Moreover, perhaps shaking or stirring the flask around would allow each enzyme and substrate to bind equally or fairly which would lead to more accurate results.
To improve the investigation, temperatures below 00C should also have been investigated, as there was oxygen production even at this temperature. Moreover, more specific temperatures should be investigated such as 300C, 320C, 340C, 360C, 380C etc to gain a specific ideal that suits the enzyme and thus causes an increased rate of reaction.
Moreover, perhaps shaking or stirring the flask around would allow each enzyme and substrate to bind equally or fairly which would lead to more accurate results.
The investigation could also be extended to combine other factors affecting the rate of reaction such as pH, enzyme concentration, presence of inhibitors, or substrate concentration.
