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Effect of pH on Catalase activity

Asked by rheasweetz | Apr 27, 2008 | AS Level > Biology > Coursework
rheasweetz asks:

I've been trying to upload the draft copt of my biology coursework but it kept on failing.

please comment on my draft coursework so that i can improve it. The exam board is QA and its the skill G. I can't upload the Skill F because it has to be hand drawn in a graph paper.

here's the coursework:

From the graph:
The plotted points joining pH 3 with pH 5 was steep.
From pH 5 to pH 7, the line became steeper.
pH 7 is where the graph reached its peak.
pH 7 to to pH 9 and from pH 9 to pH 11, the volume of of oxygen produced was rapidly decreasing from 2.7 cm3 (pH7), to 1.7 cm3 (pH 9) and then to pH 11 that has produced 1.3 cm3 of oxygen.

   There is an overall pattern of decreasing volume of oxygen when the pH level is decreased less than pH 7. In addition to that, another pattern is the decreasing volume of oxygen as the pH level is increased (more than pH 7).

   All enzymes are proteins and are therefore affected by the change in pH. Enzymes have a specific tertiary structure which is determined by the primary structure involving the sequence of amino acids. The folding and bending of the amino acid sequence is caused by the different bonds and attractions within the molecule. These bonds and attractions are the following:
Hydrogen bonds formed between hydrogen and an electronegative atom.
Ionic bonds formed between oppositely charged ions.
Van der Waals forces formed between non specific, nearby atoms.
Disulphide bridges formed between two SH containing cysteine residues.

The effect of change in pH is due to:

The breaking of hydrogen bonds. Because this bond is weak, it can therefore be easily broken by changing the concentration of hydrogen ions (H+) in the solution. The effect of pH to the activity of catalase can be accounted for by the breaking of the hydrogen bonds which is one of the most common bond in the structure of the enzyme and one of the responsible bonds for holding the tertiary structure of the enzyme together. Hence, if broken , it will affect the shape of the enzyme's active site.
The change in pH leads to the breaking of the ionic bonds which, like hydrogen bonds, are one of the bonds responsible for holding the specific structure of the active site of the enzyme which gives rise to their specificity. As a result, the catalase begins to lose its functional shape, the active site in particular. At this point, the enzyme is said to have denatured and will not be able to form a temporary enyme-substrate complex necessary for the enzyme to carry out the catalysis reaction.
Changing the pH level of the solution in which the enzyme is in affects the charges on the amino acid within the enzyme's active site. This change will unable the catalases' active site to make a temporary complex with the substrate.

Based on the graph that I have plotted, we can see that there is a decreasing trend in the volume of oxygen produced as we increase and decrease the pH level more than or less than pH 7. From this information, we can say that the optimum pH level at which the enzyme catalase works at its best and the fastest is at pH 7. Using the above results of how the change in pH can affect the rate of activity of catalase, we can deduce that the pH affects the bonding involved in keeping the tertiary structure of the active site of the enzyme. Another important effect of pH to the active site is that a change in pH, may it be higher or lower the optimum pH level alters the charge of the active site. All of these effects leads on to the denaturing of the active site which then prevents enzyme-substrate complexes to form. Thus, no substrate is catalysed which can be seen as the graph rapidly decreaesd as the pH level is decreased or increased from its optimum pH level, ph 7.


etutor answers:
This is fine and scientifically accurate. I would just point out that your results don't necessarily mean that the optimum pH is 7, but that the optimum is somewhere between 6 and 8 (as you don't have readings for 6 and 8, you can't assume they'd be less than the 7.

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