A Level Biology Revision "The Effect of pH on Enzymes" | Freesciencelessons YouTube Video Summary
This video by Freesciencelessons teaches the effect of pH on enzymes. The video starts off with how enzymes work fastest at a specific optimum pH. When the pH changes away from the optimum pH, the rate of reaction decreases because the R groups and the concentration of hydrogen ions present starts to break the bonds which can change the shape of the active site.
Detailed Summary:
The Effect of pH on Enzymes
This Freesciencelessons video aims to teach the effect of pH on enzymes. The video starts off with mentioning an enzyme catalysed reaction depends on the temperature, with enzymes working the fastest at an optimum temperature. Above the optimum temperature, the tertiary structure of the enzyme changes and the active site is no longer complementary to the substrate causing the rate to fall to zero.
pH effect on Enzymes
Enzymes are also affected by pH, the pH of a solution depends on the concentration of hydrogen ions. A solution with a low pH has a high concentration of hydrogen ions and a solution with a higher pH has a lower concentration of hydrogen ions. Each enzyme works fastest at a specific optimum pH. If the pH changes away from the optimum pH then the rate of the reaction decreases.
Hydrogen Ions Bonding
Hydrogen ions can bond with the R groups of the amino acids in the protein, this includes amino acids within the active site which form temporary bonds to the substrate. Because this can prevent the R groups from bonding with the substrate, this can reduce how effectively the substrate binds to the active site reducing the rate of the reaction. Hydrogen ions can also bond with R groups on amino acids in the rest of the enzyme molecule. The effect of this can be to break the bonds holding the tertiary structure of the enzyme in place.
Ionic Bond
Freesciencelessons uses an example of an ionic bond between two amino acids on different parts of the enzyme molecule and when the pH falls, then the concentration of hydrogen ions rises and the bond breaks. If the pH rises, then the concentration of hydrogen ions falls and now the bond breaks in this way. Changing the pH can break the bonds which are essential for the enzyme's tertiary structure. This can change the shape of the active site making it less likely that the substrate can attach successfully.
Calculation
If you're following the AQA spec, then you need to be able to calculate the pH of a solution from the concentration of hydrogen ions.
We calculate the pH using this equation: pH = -log [H+]
If you're given the concentration of hydrogen ions, first you need to enter this into your calculator, then press the log button. Be careful not to press the ln button as that is not correct. Finally, we reverse the sign of our number to get the pH.