The Effect Of Ph On The Rate Of An Enzyme Reaction

Submitted By getsomemo
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The Effect of pH on the Rate of an Enzyme Reaction
The problem being investigated in this lab is the effects of salt concentration, pH, temperature, and inhibitors on the rate of an enzyme reaction.
Background Information
If the salt concentration of a solution is very low or zero, the charged amino acid side chains of the enzyme molecules would stick together and cause the enzyme to denature and be an inactive substance. The pH scale ranges from 0 to 14. When pH is between 0 and 7, the solution is acidic. If the pH is around 7, then it is said to be neutral. If the pH is in the range of 7 to 14, then it is said to be a basic solution. As the pH of a solution is lowered, an enzyme will lose its H+ ions and eventually change its shape if enough are lost. A buffer is a compound that acts like a sponge to pick up any extra H+ or OH- ions so that a constant pH is maintained. All chemical reactions speed up as the temperature is increased because more of the reacting molecules have enough kinetic energy for the reaction to occur. Smaller molecules that are not the substrate are also allowed to interact with an enzyme. If that specific molecule increases the reaction, then it is considered an activator and if it decreases the reaction rate then it is considered an inhibitor.
If you put an enzyme into an acidic solution, then the reaction would be slowed down because the enzyme would become denatured. When
Test Tube #1 (control tube without H2O2):
0.1 mL guaiacol
1.0 mL turnip extract
8.9 mL distilled water
Test Tube #2 (substrate):
0.1 mL guaiacol
0.2 mL of 0.1% H2O2
4.7 mL distilled water
Test Tube #3 (enzyme):
1.0 mL turnip extract
4.0 mL distilled water
Test tubes
Graduated cylinder
Beakers of pH 2, 4, 8, & 10
1. 3 test tubes were labeled (#1, #2, #3)
2. Tube #1 (control tube without H2O2) had .1 mL of guaiacol, 1 mL of turnip extract, and 8.9 mL of distilled water.
3. Tube #2 (substrate) had .1 mL of guaiacol, .2 mL of .1% H2O2, and 4.7 mL of distilled water.
4. Tube #3 (enzyme) had 1 mL of turnip extract and 4 mL of distilled water.
5. The spectrophotometer was set to 500 nm.
6. The spectrophotometer was zeroed with tube #1.
7. Contents of tubes #2 and #3 were mixed, pouring the contents back and forth 2 times, and the stopwatch was started as soon as the solutions were poured together.
8. The outside of the tube was wiped with paper towel and placed in the spectrophotometer.
9. Absorbance readings were taken every 30 seconds for 3 minutes.

Graphic of Set-up

Independent Variable
The independent variable in this experiment was the pH of the solution. (how was the pH of the solution measured?)
Dependent Variable
The dependent variable in this experiment was the rate at which the enzyme reaction occurred. The reaction was measured by reading the absorbance of the particular substance every 30 seconds for a total of 3 minutes at an absorbance level of 500 nm in the spectrophotometer.

Turnip extract
Distilled water
Spectrophotometer absorbance setting (500 nm)
Readings every 30 seconds
Test tubes
Pressure of room
Temperature of room
Light exposure

Control Group
The control group in this experiment was test tube #1. It contained 0.1 mL of guaiacol, 1 mL of turnip extract, and 8.9 mL of distilled water. The control is needed to zero the spectrophotometer so that any difference in the meter reading with change in the sample will reflect a difference in the oxidized guaiacol concentration.

Discussion of Hypothesis and Data
Our group’s hypothesis was incorrect. We thought that at basic solutions, the reaction would be faster, and in acidic solutions, the reaction would be slower. The reaction was actually faster at neutral pH (6-8) rather than at extreme pH values. The steeper the line is, the higher the reaction rate is,