Introduction
Catalysis is the acceleration of a chemical reaction by a substance called a catalyst. Enzymes increase the reaction rate, causing the reaction to make more product. Proteins are large, complex molecules composed of chains of amino acids. The three-dimensional structure of a protein is critical to its function, as it determines how the protein interacts with other molecules and carries out its biological roles. The primary structure of a protein is the linear sequence of amino acids in the protein chain. The sequence of amino acids is determined by the genetic code, and can vary greatly among different proteins.
A protein’s secondary structure refers to the protein chain’s local folding patterns. Two common types of secondary structure are alpha helices and beta sheets, which are stabilized by hydrogen bonds between nearby amino acids. The tertiary structure of a protein refers to the overall three-dimensional shape of the protein. This structure is stabilized by a variety of chemical bonds, including hydrogen bonds, disulfide bonds, and hydrophobic interactions. Finally, some proteins have quaternary structure, which refers to the way that multiple protein subunits interact to form a larger, functional protein complex.
Beef liver contains a variety of proteins, including enzymes, transport proteins, and structural proteins such as collagen. Proteins in beef liver also provide essential amino acids that are necessary for proper growth and development, as well as the maintenance of healthy tissues in the body. Denaturation of proteins refers to the process by which the three-dimensional structure of a protein is disrupted or altered, leading to the loss of its biological function. There are several ways in which proteins can be denatured, including heat, pH and exposure to certain chemicals (detergents, organic solvents, or heavy metals).
The pH of a solution can greatly affect the rate of a catalyzed reaction, as the ionization state of both the catalyst and the reactants can be affected by changes in pH. A catalysis pH lab typically involves measuring the rate of a catalyzed reaction under different pH conditions. This can be done by adding a known amount of catalyst to a solution containing the reactants, and then monitoring the reaction rate over time using Pasco. The pH of the solution can be adjusted using a buffer system, which helps to maintain a constant pH by resisting changes in acidity or basicity. By varying the pH of the solution and measuring the reaction rate, it is possible to determine the optimal pH range for the catalyzed reaction and the effect of pH on the catalytic activity of the catalyst.
Question
How do changes in pH in an environment affect the reaction rate of enzymes (beef liver)?
Purpose
This lab aims to explore the effects of pH on the reaction rate of beef liver.
Hypothesis
If the pH increases or decreases beyond 7 (the optimal pH level for the enzyme catalyze), the reaction will slow down.
Materials
-4 test tubes
-One larger beaker with ice
-Pasco hardware
-Laptop computer w/ Pasco software
-3 large graduated cylinders
-One disposable pipette
-9 ml H2O2
-3 ml of pH buffer 6
-3 ml of pH buffer 7
-3 ml of pH buffer 8
-20 mL beef liver (catalase)
-3 small test tube stoppers
Procedure
-Mark a set of test tubes with a 4, 7 and 10 for the pH.
-Used the graduated cylinder to measure out 3 ml of H2O2.
-Poured 3 mL of H2O2 into each test tube.
-Obtained about 20 mL of the liquid beef liver.
-Poured the 20mL of liquid beef liver into a test tube.
-Placed the beef liver test tube in a beaker of ice to keep it chilled
-Set up a pasco interface to obtain pasco data.
-Obtained about 3 mL of each pH buffer needed for pH 6, 7 and 8.
-Measured 3 mL of pH 7 buffer solution using a clean graduated cylinder.
-Poured the 3 mL of pH 7 buffer into the test tube marked “7” which already contains H2O2.
-Set up the pasco system with the test tube marked “7”.
-Used a disposable pipette to add 2 drops of beef liver the test tube marked “7”
-Stirred the contents of the test tube marked “7” until mixed.
-Put a stopper on top of the test tube marked “7”.
Recorded observations
Repeated procedure steps 9-15, replacing the 7 pH buffer with the pH 4 buffer, then the pH 10 buffer.
Cleaned up all materials before leaving the work space.
Observations
Table 1, Oxygen gas produced as a result of pH vs. Time
| Time (Seconds) | Amount of oxygen gas produced (mL) with a buffer of pH 4 | Amount of oxygen gas produced (mL) with a buffer of pH 7 | Amount of oxygen gas produced (mL) with a buffer of pH 10 |
| 30 | 4 | 6 | 5 |
| 60 | 6.2 | 12 | 6 |
| 90 | 6.5 | 13 | 6.2 |
| 120 | 7 | 13.5 | 6.3 |
| 150 | 7 | 14 | 6.5 |
| 180 | 7 | 15 | 7 |
| 210 | 7 | 16 | 7.5 |
| 240 | 7 | 16.5 | 7.6 |
| 270 | 7 | 16.5 | 8 |
| 300 | 7 | 17 | 8 |
Table 2, pH of the solution vs kPA
| pH | kPA Of Reaction System |
| 4 | 99.8 |
| 7 | 99.7 |
| 10 | 99.65 |
Qualitative Results: Table 3, pH changes and resulting physical changes
| pH | Observations |
| 4 | Slight bubbling No change in temperature on test tube |
| 7 | Lots of bubbling Test tube felt slightly warmer |
| 10 | Slight bubbling No change in temperature on test tube |
Analysis
Graph 1: Showcases the results of the oxygen gas produced over a period of 300s as a result of the enzyme being located in an environment of pH 7.
Graph 2: Showcases the results of the oxygen gas produced over a period of 300s as a result of the enzyme being located in an environment of pH 4.
Graph 3: Showcases the results of the oxygen gas produced over a period of 300s as a result of the enzyme being located in an environment of pH 10
Graph 4: Showcases the difference in kPA and pH as it increases.
Table 4, pH of the solution vs kPA for the other group’s data collection that also tested with pH.
Graph 5: Showcases the pH of the solution vs kPA data collected by the other group that also tested with pH.
Discussion
The purpose of this lab is to explore the effects pH has on a reaction rate of beef liver and how it affects the production of oxygen gas. Catalase, an enzyme found in the liver, plays a crucial role in maintaining homeostasis by facilitating the breakdown of hydrogen peroxide into water and oxygen. It was hypothesized that the rate of reaction would slow down if the pH was at any other level than its optimal pH level. If the pH increases or decreases beyond 7 (the optimal pH level for the enzyme catalyze), the reaction will slow down.
The catalysis pH lab with beef liver aims to investigate the effect of pH on the catalytic activity of beef liver. In this experiment, beef liver is used as the catalyst to decompose hydrogen peroxide. The results show that the catalytic activity of beef liver is highly dependent on pH. The reaction rate is found to be highest at pH 7, which is the optimal pH range for the catalyzed reaction. At higher or lower pH values, the reaction rate decreases significantly, indicating that the catalytic activity is inhibited by changes in pH.
Furthermore, the experiment demonstrates the importance of buffer systems in maintaining a constant pH, which is essential for accurate measurements and consistent results. The use of buffer solutions ensures that the pH of the reaction mixture remains stable, allowing for a more precise determination of the optimal pH range for the catalyzed reaction. Overall, the catalysis pH lab with beef liver provides valuable insights into the effect of pH on catalytic activity, which is important for understanding the mechanism of enzyme-catalyzed reactions and optimizing catalytic processes in various fields.
The reaction rate was significantly slower at pH 4 and 10 compared to pH 7, as evidenced by the lower amount of gas bubbles produced. No heat was felt in the test tubes, indicating that the hydrogen and oxygen bonds in hydrogen peroxide were being broken down slower due to the denaturation of the enzyme. Enzymes can denature, or lose their three-dimensional shape and functionality, due to factors such as high temperature, extreme pH levels, or chemicals that disrupt the enzyme’s structure.
When enzymes are subjected to high temperature or extreme pH levels, the bonds holding the enzyme’s tertiary and secondary structures together break, causing the enzyme to unravel and lose its shape. This loss of shape results in the enzyme’s active site becoming distorted, impairing the enzyme’s ability to bind to its substrate and catalyze chemical reactions.
pH is a crucial factor affecting an enzyme’s shape and functionality because enzymes are proteins with specific three-dimensional structures essential for their catalytic activity. The shape of an enzyme’s active site, which is the part of the enzyme that binds to the substrate, is crucial for its functionality, as it determines the specificity of the enzyme-substrate interaction.
At the wrong pH, the enzyme’s active site can become distorted, which alters its shape, preventing the substrate from binding to it. This leads to a malfunctioning enzyme that is unable to catalyze the reaction and lower the activation energy required for the reaction to occur. The enzyme’s shape can be altered due to excess H+ or OH- ions, which disrupt the hydrogen bonds and ionic interactions that hold the enzyme’s three-dimensional structure together.
The experiment showed that at pH 7, the catalase enzyme quickly facilitated hydrogen peroxide breakdown, as evidenced by the rapid production of gas bubbles in the test tube. The breakdown process also generated heat due to breaking high-energy bonds between hydrogen and oxygen. The quantitative data collected further supported the hypothesis, showing that more oxygen was produced in the pH 7 experiment. Comparing the slopes of Graph 1 to Graphs 2 and 3, it can be concluded that pH changes significantly affect the enzyme’s functionality.
Now how does this data affect beef liver in the real world? The optimal pH level for beef liver is around 6.4 to 6.6. If the liver is mixed into a pH level that is not within this range, it can negatively impact the liver’s texture, flavor, and safety. If the pH level is too high (more alkaline), the liver may become tough and dry, as the proteins in the liver will denature and coagulate. This can make cooking and eating the liver difficult, as it may have a rubbery texture.On the other hand, if the pH level is too low (more acidic), the liver may become too soft and mushy, as the acid will break down the proteins in the liver.
This can also make cooking and eating the liver difficult, as it may have a mushy texture and an off-flavor. In addition to affecting the texture and flavor of the liver, mixing it into a pH that is not at the optimal level can also have food safety implications. The pH level of the liver can impact its susceptibility to bacterial growth, and a pH that is too high or too low can increase the risk of foodborne illness. It’s important to handle and cook beef liver properly to ensure it’s safe to eat.
When comparing the data with the observations of the other group, refer to Table 4 and Graph 5. Upon comparing the data from the other group, it was observed that the enzyme demonstrated a similar response to changes in temperature, concentration, and pH. The enzyme was denatured, and the reaction rate was slow when the temperature was too high or too low, resulting in lower pressure (kPa) outside of the optimal range. Concentration also had a similar effect on the reaction rate.
However, an interesting finding was that the kPa values for the other pH levels were not significantly different from the pH levels tested by our group. The graph showed that the change in overall pressure for pH 4, 7, and 10 was similar, which is contrary to research indicating that pressure should increase with pH. It is possible that the other group’s results may have been affected by experimental error. Our group also observed a similar pattern of little change in pressure, which could be attributed to insufficient reactants in the test tube for a significant change in pressure to occur.
Error
If gas escaped during the pH lab, it could lead to several sources of error, affecting the measurements’ accuracy and precision. During the experiment, it was noticed that it had escaped, which was evident through the slight drops in pressure as the time went on in graph 2. Fortunately, it was noticed that the group had not made the error of letting gas escape. Instead the group mis-inputted the data into the graph. To make sure the misinputting mistake does not happen in the future it is a good idea to always double check the graphs and make sure the information presented on the graph makes sense. If gas escaped from the reaction vessel, the pressure inside the vessel could change, which could affect the rate of the reaction. This could result in inaccurate measurements and lead to errors in the calculated reaction rates.
To minimize this error, it is important to ensure that the reaction vessel is tightly sealed and that any gas generated during the reaction is captured and measured. It is also important to make sure the scientist does not open the seal earlier than necessary as it will show fluctuation in pressure (gas escaping). Additionally, it is important to use appropriate equipment and techniques to accurately measure the pH and other parameters of the reaction mixture.
Conclusion
In conclusion, the catalysis pH lab provides important insights into the effect of pH on catalytic activity, which is essential for optimizing catalytic reactions in various fields. By varying the pH of the solution and measuring the reaction rate, we can determine the optimal pH range for the catalyzed reaction and understand the mechanism of the catalytic reaction. Additionally, buffer systems can be used to maintain a constant pH, which is crucial for accurate measurements and consistent results.
By understanding the impact of pH on catalytic reactions, we can better design and optimize reactions for specific applications. As the enzyme pH approached a certain “ideal pH,” the rate of enzyme activity increased. The correlation between pH and rate of enzyme activity was initially a strong positive correlation between the two variables and continued to be a positive correlation but the graph became steady over time. The results from this lab accurately reflected all three of our hypotheses. Overall, the catalysis pH lab provides a valuable learning experience for students and researchers alike, allowing them to understand the principles of catalysis and their applications in various fields.
