Enzyme Lab Report
Enzymes
Ashley Njeru
Mrs. Booth
Tuesday, March 19th 2013
SBI 4U
INTRODUCTION:
The cellular activity of all organisms is controlled through the use of enzymes. An enzyme is a special type of biological molecule, usually a protein, which speeds up a chemical reaction; most are soluble in water or a dilute salt solution. There are about 4000 different enzymes in a typical living cell. If even one of these enzymes is missing or defective, the results can disastrous. Enzymes have a unique three dimensional shape, and this shape determines which reaction it catalyzes. Another term that is used to describe an enzyme is catalyst. A catalyst is a substance that speeds up a reaction, …show more content…
without being consumed by the reaction. (5, 2) Characteristics of enzymes: The shape of the globular protein determines the function, they stress chemical bonds, and they lower the activation energy barrier (EA). This energy barrier must be overcome in order for the chemical reaction to move forward. The enzyme has surface depressions on them called active sites representing the location for catalysis. A substrate (reactant molecule on which the enzyme acts) must fit into the active site perfectly. The enzyme stresses the chemical bond and therefore lowers the activation need to break a bond. (1)
There are many factors that can alter enzyme activity, the most common being temperature and pH level. When temperature levels begin to increase, the rate of the reaction increases as well because the increased kinetic motion in the molecules begins to get stronger and stronger. However, this can only go so far. Once the temperature reaches a certain peak, the kinetic motion begins to denature an enzyme and eventually the enzyme will lose its ability to function.
Enzymes require very specific conditions for them to work appropriately. Typically, each enzyme has an optimal pH level where it operates at its highest efficiency. The rate of the catalyzed reaction will decrease when the pH level either increases or decreases away from its optimal value.(1) The rate of reactions of the enzymes can be further determined with the help of hydrogen peroxide. By placing various hydrogen peroxide solutions with different pH levels in the catalase, this aids in determining the action of catalse to a non-protein catalyst. (6)
PURPOSE:
The following experiment was to compare the action of catalase to a non-protein catalyst under different conditions.
MATERIALS:
|3% hydrogen peroxide |Sand |
|Manganese dioxide |Mortar and pestle |
|Liver |Hot plate |
|Potato |600mL beaker |
|Ice |Test tubes |
|Acidic acid |Scalpel |
|4.0 M NaOH | |
PROCEDURE:
PART A: Effect on temperature.
Place a small piece of liver in a test tube and heat until sections C-F are complete in a boiling water bath. Add 2mL of hydrogen peroxide and record your results.
Place a small piece of liver into each of the 2 test tubes. Place one test tube in a 37oC water bath until sections C-F are completed and the second test tube in ice-water until sections C-F are completed. Remove both test tubes and add 2mL of hydrogen peroxide and record your rates of reaction.
PART B: The effects of pH on an Enzyme.
Place 2mL of acidic acid, 4.0 M NaOH and distilled water respectively into 3 test tubes. To each of these solutions place a small piece of liver and let until sections C-F are completed. Once completed drain the initial liquid and add 2 mL of hydrogen peroxide and record the rate of reaction for each of the test tubes.
PART C: Catalytic reactions.
Add 2mL of hydrogen peroxide to 2 test tubes. Place a pinch of sand in one test tube and add a pinch of manganese dioxide to the second tube. Observe and record the rates of reaction. What gas evolves?
PART D: The effect of an enzyme.
Add 2 mL of hydrogen peroxide to each of the 2 clean test tubes. In one place a small piece of liver and in the other a small piece of potato. Record the rates of the reaction and compare these results to those with MnO2. Do not discard these materials!
PART E: Re-using an enzyme.
Divide the liquid portion of the previous tube in D containing the liver into 2 test tubes. Cut the liver from procedure D into 2 equal portions and add these to the 2 test tubes. To the first add a fresh piece of liver and to the second add 1 mL of hydrogen peroxide. Record your observations and explain the reaction in the test tube containing the fresh liver. What would happen if additional hydrogen peroxide were added to the second tube?
PART F: Effect on particle size.
Place a small piece of liver in the mortar and pestle and crush it up. Place this in a clean test tube. Repeat the procedure for a small piece of potato. Add 2 mL of hydrogen peroxide to each test tube and record the rates of reaction. Compare the results with those of the uncrushed liver and potato in Part B.
OBSERVATIONS: Rates of reaction are designed as followed: 0-no reaction, 1-slow, 2-moderate, 3-fast, 4-very fast.
|Tests | |Observations |Rate of Reaction |
|PART A |Boiled liver |Hydrogen peroxide evaporated |Slow reaction (after hydrogen peroxide |
| | |Liver dried out |was added) |
| | |Minimal bubbles formed (after hydrogen peroxide was |1 |
| | |added) | |
| |37oC liver |Liver did not change in shape or colour |Very fast reaction (after hydrogen |
| | |Hydrogen peroxide evaporated |peroxide was added) |
| | |Bubbles rose and was large in size (after hydrogen |4 |
| | |peroxide was added) | |
| |Liver at 0oC |Hydrogen peroxide evaporated |Moderate reaction (after hydrogen |
| | |Liver did not change in size or shape |peroxide was added) |
| | |Bubbles rose and was large in size |2 |
| | |(after hydrogen peroxide was added) | |
|PART B |Liver in acidic acid |Liver had a change in colour to a lighter, brownish |Slow reaction |
| | |colour |1 |
| | |Minimal formation of bubbles; did not rise (after | |
| | |hydrogen peroxide was added) | |
| |Liver in distilled water |Liver had a change in colour to a lighter, brownish |Fast reaction …show more content…
|
| | |colour |3 |
| | |Hydrogen peroxide had a slight colour change | |
| | |Bubbles rose very rapidly | |
| |Liver in 4.0 M NaOH |Liver did not have any shape or colour change |Moderate paced reaction |
| | |Temperature of test tube became colder |2 |
| | |There was a formation of bubbles but they did not rise| |
|PART C |Sand |Sand sunk to bottom of test tube |No reaction |
| | | |0 |
| |MnO2 |Solution dissolved in hydrogen peroxide |Very fast reaction |
| | |There was bubbling and fizzing once in contact with |4 |
| | |hydrogen peroxide | |
| | |Colour change in solution to black | |
| | | | |
| | |Temperature of test tube became warmer | |
|PART D |Liver |Solution was bubbling and bubbles rose up |Very fast reaction |
| | |Temperature changed to a warmer temperature |4 |
| | |Solution had a slight change in colour | |
| |Potato |Solution was bubbling |Moderate reaction |
| | |Potato had bubbles surrounding it |2 |
|PART E |Used liver and fresh liver |Solution had a change in temperature; colder |Slow reaction |
| | | |1 |
| |Used liver and H2O2 |After H2O2 was placed, bubbles began to form very |Very fast reaction |
| | |rapidly and began to rise quickly |4 |
|PART F |Crushed liver |Once hydrogen peroxide came into contact with liver, |Fast reaction |
| | |large bubbles began to form |3 |
| | |Bubbles rose rapidly | |
| |Crushed potato |There was a slower formation of bubbles and were |Slow reaction |
| | |smaller in size |2
|
| | |Bubbles rose only a bit | |
DISCUSSION:
Part A – Boiling Liver:
When the liver was placed in the water with the hydrogen peroxide and began to boil, the hydrogen peroxide began to evaporate the longer the test tube remained in the water and the higher the temperature rose. After sections C-F were completed, the hydrogen peroxide in the test tube was completely evaporated and the liver was left alone in the tube. The liver looked shriveled up and due to the extensive high heat and with all the hydrogen peroxide gone, it was all dried out. Once a new batch of hydrogen peroxide was placed in the test tube, bubbles began to form although the reaction was very slow. The reaction occurred at a very slow rate because when boiling an enzyme, its natural qualities are being altered; the enzyme is denatured. When a protein denatures, it can no longer be used because all its properties have been altered. When this happens, the catalase can no longer fit into the substrate molecules t break them down.
37oC liver:
When the liver was placed in the 37oC water along with the hydrogen peroxide, no reaction occurred except that after sections C-F were completed, there was no trace of hydrogen peroxide; because this water was not being boiled, hydrogen peroxide could not have been evaporated but could have been dissolved by the liver over the course of time the test tube was in the 37oC water, although, the liver did not change in colour. When another set of hydrogen peroxide was placed in the test tube, bubbles that were large in size began to form at a very fast rate and these bubbles began to rise up the test tube.
Liver at 0oC:
When the liver was placed in iced water along with the hydrogen peroxide, no reaction occurred except that after sections C-f were completed, the hydrogen peroxide was gone and the liver did not have any changes physically. The possibility that it could have been dissolved by the liver is high. Once hydrogen peroxide was added again into the test tube, large bubbles began to form and rise at a moderate rate. The freezing temperature causes the reaction to slow down and therefore reduces the reaction rate. (4)
Part B – Liver in acidic acid:
When the liver was placed initially in the acidic acid and was sitting in the liquid until sections C-F was completed, the liver had a change in colour to a much lighter, brownish colour. The acidic acid did not evaporate nor did it get dissolved, but it remained in the test tube with no change to it. Once the acidic acid was replaced with hydrogen peroxide, small bubbles began to form and did not grow nor did it rise. The rate if this reaction was very slow.
Liver in distilled water:
When the liver was placed initially in the distilled water and was kept sitting in the liquid until sections C-F was completed, the liver changed in colour; it had a lighter, brownish colour to it. The distilled water did not have any physical change to it. Once the hydrogen peroxide became the replacement for distilled water and came into contact with the liver, the hydrogen peroxide had a slight change in colour; seemed as if some colour of the liver was dissolved into the hydrogen peroxide and the solution had the colour of the liver, although, the liver did not have any physical change when hydrogen peroxide was placed in the test tube. Bubbles also began to form and rise very rapidly; this reaction occurred at a very fast rate.
Liver in 4.0 M NaOH:
When the liver was placed initially in the NaOH and was sitting in the liquid until sections C-F was completed, the liver nor did the NaOH have any colour change to it, although, the solution became colder in temperature. Once the hydrogen peroxide was placed in the test tube in place for the NaOH, the only reaction was the formation of bubbles but they did not rise. This reacting occurred at a moderately paced rate.
The pH level on an enzyme activity can have a great effect on it. When the liver was placed in a lower ph level (acidic acid) the liver becomes ‘cooked’ but occurs at a slower rate. When the liver was placed in a higher ph level solution (NaOH) the reaction rate was almost as similar to the rate of the neutral (distilled water) solution, which were both faster than the acidic acid. (6)
Part C-Sand:
When the sand was placed in the hydrogen peroxide no reaction occurred; no change in colour, no chemical reaction, just that the sand sank to the bottom of the test tube.
Manganese dioxide:
When the manganese dioxide came into contact with the hydrogen peroxide, the solution began to bubble which created a fizzing sound and the manganese dioxide dissolved in the hydrogen peroxide. The solution changed to a black colour and the temperature also changed to a warmer temperature. When manganese dioxide and hydrogen peroxide combine, they form water and an oxygen gas: MnO2 + 2H2O2 => MnO2 + O2 + 2H2O. (3)
Part D-Liver:
When the liver is placed into the hydrogen peroxide, the reaction forms bubbling in the solution and causes it to rise up the test tube. The solution also changes colour and becomes warmer in temperature, therefore the reaction was exothermic. This reaction occurred in a very fast rate.
Potato:
When the potato was placed into the hydrogen peroxide, bubbles began to form and were surrounding the potato. No physical change occurred to the potato nor was there any change in the solution. This reaction was at a slow rate.
The potato contained less catalase than the liver because the rate of reaction for the liver occurred at a very fast rate where as the reaction rate for the potato occurred at a much slower rate; the rate of reaction tells how much catalase is contained in each.
Part E-Used liver and fresh liver:
The used liver and the fresh liver did not have any change to it; no reaction occurred. The only change was the colder temperature to the solution when the fresh liver was newly added into the solution, but this reaction occurred at a slow rate.
Used liver and H2O2:
When the newly added hydrogen peroxide was placed into the test tube with the used liver, the very fast paced reaction caused bubbles to form very quickly and began to rise up the test tube at a very fast pace as well.
Part F-Crushed liver:
When the crushed liver was placed in the hydrogen peroxide solution, large bubbles began to form at a fast rate and began to rise up the test tube as well.
Crushed potato:
When the crushed potato was placed in the hydrogen peroxide solution, small bubbles began to form however, the formation of these bubbles occurred at a slower rate than the crushed liver.
The crushed liver still contains more catalase than the potato, causing the reaction to occur at a faster rate, although, this time, because the pieces are smaller, the rate will occur faster than when it is in solid form.
Error analysis:
There were a number of students conducting the same experiment at once and within each group there were at least 2-3 students observing what the rate of reaction was, therefore the recorded rate of reaction may have not been accurate. Each step of the experiment was only completed once and not repeated multiple times to ensure the precision of the recorded data causing the possibility that the recorded rate of reactions were not accurate. There were a limited number of test tubes to use a completely clean one every time because of the number of students using the test tubes and of course the limited number of test tubes during the experiment. If the test tubes were not completely rinsed out, this may have affected some of the reaction rates.
CONCLUSION:
1. The speed of chemical reactions are determined by:
a. The amount of activation energy needed
b. The concentration and effectiveness of catalysts
There are several factors that can affect enzyme activity, including enzyme and substrate concentration, temperature, and pH level. Any changes in temperature, substrate concentration, and pH level can disrupt the bonds of the protein (enzyme) and denature it, therefore changing the shape of the protein so it will no longer function. Most human enzymes work best at 37oC allosetric sites in an enzyme. (1) Size can also alter enzyme activity; the smaller the particle size the faster the reaction rate. In each of the steps of the experiment, the recorded rates were different for each because the temperature, ph level and even the size of the liver were altered to conduct and compare the action of catalase to a non-protein catalyst under the different conditions.
2. Hydrogen peroxide can be broken down by catalysts other than those found in living systems because hydrogen peroxide is an unstable compound composed of hydrogen and oxygen. There are several inorganic substances that catalyze its decomposition, including most transition metals and their compounds such as manganese dioxide. Hydrogen peroxide breaks down exothermically into 2H2O + O2; water and oxygen.
3. Changes in temperature strongly affect the activity of most enzymes. As the temperature increases, the rate of the chemical reaction increases as well. The increase in chemical reactions reflects the increase in the kinetic motion of the molecules. As the temperature increases, the molecules tend to have more frequent and stronger collisions. As the kinetic motion increases, it may reach a peak where it begins to unravel, or denature, an enzyme.
The bonds and other forces that hold the enzyme breaks and at this point, the rate of the reaction drops very steeply to a zero. The enzyme then loses its ability to function. (4)
Changes in particle size also affect enzyme activity. The smaller the particle size the faster the reaction will take place because there is a larger surface area giving the particles more space for them to react.
4. Yes the results would have been different if the dog liver was used instead in the experiment because it would have been a change in temperature. A change in temperature is one of the affecting factors of enzyme activity. Any changes in temperature, whether higher or lower, can disrupt the bonds of the protein (enzyme) and denature it, therefore changing the shape of the protein so it will no longer function. The results would have been different and can be observed through its reaction rates. If the initial liver used in the experiment happened to be colder than the dog liver, the reaction rates for each step for the dog liver would have been faster because the dog liver would have a higher temperature than the initial liver. The opposite would have happened if the initial liver had a higher temperature than the dog liver; the dog liver would have reacted to each step in the experiment at a slower rate.
Cited Works:
1. Nelson Biology 12 Textbook
2. http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/E/Enzymes.html#pHandTemp
3. http://resources.schoolscience.co.uk/johnsonmatthey/page39.htm
4. http://www.worthington-biochem.com/introbiochem/tempeffects.html
5. http://www.absorblearning.com/chemistry/demo/units/LR1505.html
6. http://www.worthington-biochem.com/introbiochem/effectspH.html
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FIGURE 1 As the temperature increases, the rate of the enzyme-catalyzed reaction increases until the enzyme begins to denature. At this point, the rate of the reaction drops off steeply to a zero.
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10
Ashley Njeru
Mrs. Booth
Tuesday, March 19th 2013
SBI 4U
INTRODUCTION:
The cellular activity of all organisms is controlled through the use of enzymes. An enzyme is a special type of biological molecule, usually a protein, which speeds up a chemical reaction; most are soluble in water or a dilute salt solution. There are about 4000 different enzymes in a typical living cell. If even one of these enzymes is missing or defective, the results can disastrous. Enzymes have a unique three dimensional shape, and this shape determines which reaction it catalyzes. Another term that is used to describe an enzyme is catalyst. A catalyst is a substance that speeds up a reaction, …show more content…
without being consumed by the reaction. (5, 2) Characteristics of enzymes: The shape of the globular protein determines the function, they stress chemical bonds, and they lower the activation energy barrier (EA). This energy barrier must be overcome in order for the chemical reaction to move forward. The enzyme has surface depressions on them called active sites representing the location for catalysis. A substrate (reactant molecule on which the enzyme acts) must fit into the active site perfectly. The enzyme stresses the chemical bond and therefore lowers the activation need to break a bond. (1)
There are many factors that can alter enzyme activity, the most common being temperature and pH level. When temperature levels begin to increase, the rate of the reaction increases as well because the increased kinetic motion in the molecules begins to get stronger and stronger. However, this can only go so far. Once the temperature reaches a certain peak, the kinetic motion begins to denature an enzyme and eventually the enzyme will lose its ability to function.
Enzymes require very specific conditions for them to work appropriately. Typically, each enzyme has an optimal pH level where it operates at its highest efficiency. The rate of the catalyzed reaction will decrease when the pH level either increases or decreases away from its optimal value.(1) The rate of reactions of the enzymes can be further determined with the help of hydrogen peroxide. By placing various hydrogen peroxide solutions with different pH levels in the catalase, this aids in determining the action of catalse to a non-protein catalyst. (6)
PURPOSE:
The following experiment was to compare the action of catalase to a non-protein catalyst under different conditions.
MATERIALS:
|3% hydrogen peroxide |Sand |
|Manganese dioxide |Mortar and pestle |
|Liver |Hot plate |
|Potato |600mL beaker |
|Ice |Test tubes |
|Acidic acid |Scalpel |
|4.0 M NaOH | |
PROCEDURE:
PART A: Effect on temperature.
Place a small piece of liver in a test tube and heat until sections C-F are complete in a boiling water bath. Add 2mL of hydrogen peroxide and record your results.
Place a small piece of liver into each of the 2 test tubes. Place one test tube in a 37oC water bath until sections C-F are completed and the second test tube in ice-water until sections C-F are completed. Remove both test tubes and add 2mL of hydrogen peroxide and record your rates of reaction.
PART B: The effects of pH on an Enzyme.
Place 2mL of acidic acid, 4.0 M NaOH and distilled water respectively into 3 test tubes. To each of these solutions place a small piece of liver and let until sections C-F are completed. Once completed drain the initial liquid and add 2 mL of hydrogen peroxide and record the rate of reaction for each of the test tubes.
PART C: Catalytic reactions.
Add 2mL of hydrogen peroxide to 2 test tubes. Place a pinch of sand in one test tube and add a pinch of manganese dioxide to the second tube. Observe and record the rates of reaction. What gas evolves?
PART D: The effect of an enzyme.
Add 2 mL of hydrogen peroxide to each of the 2 clean test tubes. In one place a small piece of liver and in the other a small piece of potato. Record the rates of the reaction and compare these results to those with MnO2. Do not discard these materials!
PART E: Re-using an enzyme.
Divide the liquid portion of the previous tube in D containing the liver into 2 test tubes. Cut the liver from procedure D into 2 equal portions and add these to the 2 test tubes. To the first add a fresh piece of liver and to the second add 1 mL of hydrogen peroxide. Record your observations and explain the reaction in the test tube containing the fresh liver. What would happen if additional hydrogen peroxide were added to the second tube?
PART F: Effect on particle size.
Place a small piece of liver in the mortar and pestle and crush it up. Place this in a clean test tube. Repeat the procedure for a small piece of potato. Add 2 mL of hydrogen peroxide to each test tube and record the rates of reaction. Compare the results with those of the uncrushed liver and potato in Part B.
OBSERVATIONS: Rates of reaction are designed as followed: 0-no reaction, 1-slow, 2-moderate, 3-fast, 4-very fast.
|Tests | |Observations |Rate of Reaction |
|PART A |Boiled liver |Hydrogen peroxide evaporated |Slow reaction (after hydrogen peroxide |
| | |Liver dried out |was added) |
| | |Minimal bubbles formed (after hydrogen peroxide was |1 |
| | |added) | |
| |37oC liver |Liver did not change in shape or colour |Very fast reaction (after hydrogen |
| | |Hydrogen peroxide evaporated |peroxide was added) |
| | |Bubbles rose and was large in size (after hydrogen |4 |
| | |peroxide was added) | |
| |Liver at 0oC |Hydrogen peroxide evaporated |Moderate reaction (after hydrogen |
| | |Liver did not change in size or shape |peroxide was added) |
| | |Bubbles rose and was large in size |2 |
| | |(after hydrogen peroxide was added) | |
|PART B |Liver in acidic acid |Liver had a change in colour to a lighter, brownish |Slow reaction |
| | |colour |1 |
| | |Minimal formation of bubbles; did not rise (after | |
| | |hydrogen peroxide was added) | |
| |Liver in distilled water |Liver had a change in colour to a lighter, brownish |Fast reaction …show more content…
|
| | |colour |3 |
| | |Hydrogen peroxide had a slight colour change | |
| | |Bubbles rose very rapidly | |
| |Liver in 4.0 M NaOH |Liver did not have any shape or colour change |Moderate paced reaction |
| | |Temperature of test tube became colder |2 |
| | |There was a formation of bubbles but they did not rise| |
|PART C |Sand |Sand sunk to bottom of test tube |No reaction |
| | | |0 |
| |MnO2 |Solution dissolved in hydrogen peroxide |Very fast reaction |
| | |There was bubbling and fizzing once in contact with |4 |
| | |hydrogen peroxide | |
| | |Colour change in solution to black | |
| | | | |
| | |Temperature of test tube became warmer | |
|PART D |Liver |Solution was bubbling and bubbles rose up |Very fast reaction |
| | |Temperature changed to a warmer temperature |4 |
| | |Solution had a slight change in colour | |
| |Potato |Solution was bubbling |Moderate reaction |
| | |Potato had bubbles surrounding it |2 |
|PART E |Used liver and fresh liver |Solution had a change in temperature; colder |Slow reaction |
| | | |1 |
| |Used liver and H2O2 |After H2O2 was placed, bubbles began to form very |Very fast reaction |
| | |rapidly and began to rise quickly |4 |
|PART F |Crushed liver |Once hydrogen peroxide came into contact with liver, |Fast reaction |
| | |large bubbles began to form |3 |
| | |Bubbles rose rapidly | |
| |Crushed potato |There was a slower formation of bubbles and were |Slow reaction |
| | |smaller in size |2
|
| | |Bubbles rose only a bit | |
DISCUSSION:
Part A – Boiling Liver:
When the liver was placed in the water with the hydrogen peroxide and began to boil, the hydrogen peroxide began to evaporate the longer the test tube remained in the water and the higher the temperature rose. After sections C-F were completed, the hydrogen peroxide in the test tube was completely evaporated and the liver was left alone in the tube. The liver looked shriveled up and due to the extensive high heat and with all the hydrogen peroxide gone, it was all dried out. Once a new batch of hydrogen peroxide was placed in the test tube, bubbles began to form although the reaction was very slow. The reaction occurred at a very slow rate because when boiling an enzyme, its natural qualities are being altered; the enzyme is denatured. When a protein denatures, it can no longer be used because all its properties have been altered. When this happens, the catalase can no longer fit into the substrate molecules t break them down.
37oC liver:
When the liver was placed in the 37oC water along with the hydrogen peroxide, no reaction occurred except that after sections C-F were completed, there was no trace of hydrogen peroxide; because this water was not being boiled, hydrogen peroxide could not have been evaporated but could have been dissolved by the liver over the course of time the test tube was in the 37oC water, although, the liver did not change in colour. When another set of hydrogen peroxide was placed in the test tube, bubbles that were large in size began to form at a very fast rate and these bubbles began to rise up the test tube.
Liver at 0oC:
When the liver was placed in iced water along with the hydrogen peroxide, no reaction occurred except that after sections C-f were completed, the hydrogen peroxide was gone and the liver did not have any changes physically. The possibility that it could have been dissolved by the liver is high. Once hydrogen peroxide was added again into the test tube, large bubbles began to form and rise at a moderate rate. The freezing temperature causes the reaction to slow down and therefore reduces the reaction rate. (4)
Part B – Liver in acidic acid:
When the liver was placed initially in the acidic acid and was sitting in the liquid until sections C-F was completed, the liver had a change in colour to a much lighter, brownish colour. The acidic acid did not evaporate nor did it get dissolved, but it remained in the test tube with no change to it. Once the acidic acid was replaced with hydrogen peroxide, small bubbles began to form and did not grow nor did it rise. The rate if this reaction was very slow.
Liver in distilled water:
When the liver was placed initially in the distilled water and was kept sitting in the liquid until sections C-F was completed, the liver changed in colour; it had a lighter, brownish colour to it. The distilled water did not have any physical change to it. Once the hydrogen peroxide became the replacement for distilled water and came into contact with the liver, the hydrogen peroxide had a slight change in colour; seemed as if some colour of the liver was dissolved into the hydrogen peroxide and the solution had the colour of the liver, although, the liver did not have any physical change when hydrogen peroxide was placed in the test tube. Bubbles also began to form and rise very rapidly; this reaction occurred at a very fast rate.
Liver in 4.0 M NaOH:
When the liver was placed initially in the NaOH and was sitting in the liquid until sections C-F was completed, the liver nor did the NaOH have any colour change to it, although, the solution became colder in temperature. Once the hydrogen peroxide was placed in the test tube in place for the NaOH, the only reaction was the formation of bubbles but they did not rise. This reacting occurred at a moderately paced rate.
The pH level on an enzyme activity can have a great effect on it. When the liver was placed in a lower ph level (acidic acid) the liver becomes ‘cooked’ but occurs at a slower rate. When the liver was placed in a higher ph level solution (NaOH) the reaction rate was almost as similar to the rate of the neutral (distilled water) solution, which were both faster than the acidic acid. (6)
Part C-Sand:
When the sand was placed in the hydrogen peroxide no reaction occurred; no change in colour, no chemical reaction, just that the sand sank to the bottom of the test tube.
Manganese dioxide:
When the manganese dioxide came into contact with the hydrogen peroxide, the solution began to bubble which created a fizzing sound and the manganese dioxide dissolved in the hydrogen peroxide. The solution changed to a black colour and the temperature also changed to a warmer temperature. When manganese dioxide and hydrogen peroxide combine, they form water and an oxygen gas: MnO2 + 2H2O2 => MnO2 + O2 + 2H2O. (3)
Part D-Liver:
When the liver is placed into the hydrogen peroxide, the reaction forms bubbling in the solution and causes it to rise up the test tube. The solution also changes colour and becomes warmer in temperature, therefore the reaction was exothermic. This reaction occurred in a very fast rate.
Potato:
When the potato was placed into the hydrogen peroxide, bubbles began to form and were surrounding the potato. No physical change occurred to the potato nor was there any change in the solution. This reaction was at a slow rate.
The potato contained less catalase than the liver because the rate of reaction for the liver occurred at a very fast rate where as the reaction rate for the potato occurred at a much slower rate; the rate of reaction tells how much catalase is contained in each.
Part E-Used liver and fresh liver:
The used liver and the fresh liver did not have any change to it; no reaction occurred. The only change was the colder temperature to the solution when the fresh liver was newly added into the solution, but this reaction occurred at a slow rate.
Used liver and H2O2:
When the newly added hydrogen peroxide was placed into the test tube with the used liver, the very fast paced reaction caused bubbles to form very quickly and began to rise up the test tube at a very fast pace as well.
Part F-Crushed liver:
When the crushed liver was placed in the hydrogen peroxide solution, large bubbles began to form at a fast rate and began to rise up the test tube as well.
Crushed potato:
When the crushed potato was placed in the hydrogen peroxide solution, small bubbles began to form however, the formation of these bubbles occurred at a slower rate than the crushed liver.
The crushed liver still contains more catalase than the potato, causing the reaction to occur at a faster rate, although, this time, because the pieces are smaller, the rate will occur faster than when it is in solid form.
Error analysis:
There were a number of students conducting the same experiment at once and within each group there were at least 2-3 students observing what the rate of reaction was, therefore the recorded rate of reaction may have not been accurate. Each step of the experiment was only completed once and not repeated multiple times to ensure the precision of the recorded data causing the possibility that the recorded rate of reactions were not accurate. There were a limited number of test tubes to use a completely clean one every time because of the number of students using the test tubes and of course the limited number of test tubes during the experiment. If the test tubes were not completely rinsed out, this may have affected some of the reaction rates.
CONCLUSION:
1. The speed of chemical reactions are determined by:
a. The amount of activation energy needed
b. The concentration and effectiveness of catalysts
There are several factors that can affect enzyme activity, including enzyme and substrate concentration, temperature, and pH level. Any changes in temperature, substrate concentration, and pH level can disrupt the bonds of the protein (enzyme) and denature it, therefore changing the shape of the protein so it will no longer function. Most human enzymes work best at 37oC allosetric sites in an enzyme. (1) Size can also alter enzyme activity; the smaller the particle size the faster the reaction rate. In each of the steps of the experiment, the recorded rates were different for each because the temperature, ph level and even the size of the liver were altered to conduct and compare the action of catalase to a non-protein catalyst under the different conditions.
2. Hydrogen peroxide can be broken down by catalysts other than those found in living systems because hydrogen peroxide is an unstable compound composed of hydrogen and oxygen. There are several inorganic substances that catalyze its decomposition, including most transition metals and their compounds such as manganese dioxide. Hydrogen peroxide breaks down exothermically into 2H2O + O2; water and oxygen.
3. Changes in temperature strongly affect the activity of most enzymes. As the temperature increases, the rate of the chemical reaction increases as well. The increase in chemical reactions reflects the increase in the kinetic motion of the molecules. As the temperature increases, the molecules tend to have more frequent and stronger collisions. As the kinetic motion increases, it may reach a peak where it begins to unravel, or denature, an enzyme.
The bonds and other forces that hold the enzyme breaks and at this point, the rate of the reaction drops very steeply to a zero. The enzyme then loses its ability to function. (4)
Changes in particle size also affect enzyme activity. The smaller the particle size the faster the reaction will take place because there is a larger surface area giving the particles more space for them to react.
4. Yes the results would have been different if the dog liver was used instead in the experiment because it would have been a change in temperature. A change in temperature is one of the affecting factors of enzyme activity. Any changes in temperature, whether higher or lower, can disrupt the bonds of the protein (enzyme) and denature it, therefore changing the shape of the protein so it will no longer function. The results would have been different and can be observed through its reaction rates. If the initial liver used in the experiment happened to be colder than the dog liver, the reaction rates for each step for the dog liver would have been faster because the dog liver would have a higher temperature than the initial liver. The opposite would have happened if the initial liver had a higher temperature than the dog liver; the dog liver would have reacted to each step in the experiment at a slower rate.
Cited Works:
1. Nelson Biology 12 Textbook
2. http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/E/Enzymes.html#pHandTemp
3. http://resources.schoolscience.co.uk/johnsonmatthey/page39.htm
4. http://www.worthington-biochem.com/introbiochem/tempeffects.html
5. http://www.absorblearning.com/chemistry/demo/units/LR1505.html
6. http://www.worthington-biochem.com/introbiochem/effectspH.html
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FIGURE 1 As the temperature increases, the rate of the enzyme-catalyzed reaction increases until the enzyme begins to denature. At this point, the rate of the reaction drops off steeply to a zero.
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