12th Grade Biology Enzyme Lab Report
ENZYME LAB REPORT
Dynah Parlee
11.16.2018
12TH GRADE BIOLOGY
PURPOSE
To observe the action of the enzyme1 catalase as it breaks down hydrogen peroxide, and to compare its action to that of an inorganic catalyst (MnO2). Other factors affecting the reaction rate of catalase include: temperature, pH, surface area, and whether or not catalase and its substrate (peroxide) are reusable.
HYPOTHESIS
For part E in the lab, the slice of liver that is submersed in the 37 degree will have the fastest reaction rate, as it has the optimum temperature. As the boiled liver will likely be completely cooked after 5 minutes, all of its proteins will be denatured and so will not react with the H2O2, or only react slightly. The liver submersed in the ice bath will not react as quickly as the 37 degree liver because of its lower temperature (and therefore less energy), but since all of its enzymes are still functional, its reaction will be much greater than the boiled liver.
For Par C in the lab, the result will depend on whether there is more reactants left over in the used liver or in the used H2O2. Leftover reactants are more likely to be useable in the H2O2, as the unused reactant in the liver are close to the center and unable to take part. This means that the reaction with fresh liver and used H2O2 will have more usable reactants and therefore a larger reaction.
For part F in the lab,
MATERIALS
- 3% H2O2
- MnO2
- Stirring rods
- Ice
- Test tubes
- scalpel/razor blades
- Fresh or frozen liver
- Potato
- Cork borer
PROCEDURE
See lab hand out “the Enzyme Lab” for full Procedure
DATA
Procedure | Sample | Observations | Rxn rate | Interpretations |
A | MnO2 | Black colour, little bubbles | 2 | To establish baseline |
B | Liver | Bubbled very quickly at first, but then slowed down almost immediately | 3 | To establish baseline |
Potato | Bubbles covered potato’s surface, but very few rose to the top of the liquid | 1 | To establish baseline | |
C | Used liver + fresh H2O2 | Bubbles rose about 6 cm above the liquid | 3 | Enzymes in liver are reusable, however it seems that some ended up in the liquid previously used as there was a smaller reaction than before |
Fresh liver + used H2O2 | Few tiny bubbles, but barely any reaction | 1 | H2O2 is not reusable, but there was still a small amount of usable reactant leftover | |
D | Minced liver | Bubbles faster and longer than baseline. Reaction was steady and only slowed at the very end. | 3.5 | Minced liver is more efficient to use than the baseline as it has more surface area and therefore more usable enzymes. |
Minced potato | Started bubbling quickly, but stopped bubbling within 2 seconds | 2 | Minced potato is more efficient to use than the baseline as it has more surface area and therefore more usable enzymes. | |
E | Boiled liver | No reaction | 0 | Once the liver reaches 100 degrees it becomes cooked, meaning its enzymes are denatured and can no longer react |
37 degree liver | Bubbled steadily until it reached the top of the test tube | 4.5 | Judging by the reaction rate 37 degrees is very close to optimal temperature2. The higher temperature gives more energy without denaturing the enzymes, meaning the enzymes are all fully functional, and it also gives the reaction more energy, speeding it up | |
0 degree liver | Warmer at the bottom of the test tube (near the reaction) but remained cool at the top. Steady bubbling | 3 | Reaction is exothermic, enzymes are still capable of reacting, but are not as efficient as to 37 degree liver | |
F | Liver + HCl | Very little reaction | 1 | The addition of the acid denatured a majority of the enzymes |
Liver + H2O | Very quick reaction, continued bubbling for more than 2 minutes | 5 | The original pH level was closest to optimum out of the three test tubes | |
Liver + NaOH | Slow steady bubbles, a couple of cm above the top of the test tube | 4 | The addition of the base denatured a few of the enzymes, but it seems the optimal pH is in between neutral and basic as the test tube with base was close in reaction rate to the one with water. |
RESULTS
- The enzyme catalase kickstarts the catabolic reaction of the substrate Hydrogen Peroxide breaking down into water and oxygen.
2H2O2 + catalase→ 2H2O +O2
- Factors tested for their effect on this reaction are; surface area, temperature, pH, and the reuse of materials. Surface area made the reaction quicker, temperature increased the reaction until it started to denature the enzymes, when the pH became more acidic it denatured many of the enzymes and made the reaction much slower, and when the pH became more basic it denatured few of the enzymes and only slightly decreased the reaction speed.
- A possible explanation for the difference between the reaction rate of the liver and potato is the potato contains less of the enzyme catalase.
- H2O2 can be broken down by catalysts other than those found in living systems as demonstrated in procedure A.
- While it is hard to be certain if the experiment would change if the liver of a dog was used instead, if we assume that the optimum temperature of the liver that was used was 37 degrees, then the optimum temperature would have been 3 degrees higher.
- As it can be determined from the lab results, catalase is reusable as in part C the reused liver still had a reaction that was almost at the same level as that of the unused liver. Also, a catalyst by definition is neither a reactant or product meaning it’s not used up in the reaction.
- The graph shows the decrease in energy needed to start a reaction once an enzyme is added to the reaction.
CONCLUSION
The hypothesis for part E was completely correct, however for part C in the lab the fact that enzymes are reusable was not taken into account, and so they were treated as a single use reactant. This threw off the rest of the hypothesis. The hypothesis for part F was mostly correct but the reaction that had the added NaOH, which still had a slower reaction then the one with water, reacted at a much quicker rate than expected.
This lab demonstrates that enzymes are reusable and will keep reacting until denatured by a large change in pH, or having a temperature over their optimum temp. Taking the labs results into account, it can be assumed that the most efficient reaction involving catalase would take place at about 37 degrees, with minced liver and fresh materials.Areas for further inquiry could be made into experiments with different freshnesses of liver, and how different types of animal liver affect the reaction rate.