In non-enzyme-catalyzed reactions, the reaction rate increases as the concentration of reactant is increased. In an enzyme-catalyzed reaction, the reaction rate initially increases as the substrate concentration is increased but then begins to level off, so that the increase in reaction rate becomes less and less as the substrate concentration increases.
Explain this difference. An enzyme has an optimum pH of 7. What is most likely to happen to the activity of the enzyme if the pH drops to 6. What is most likely to happen to the activity of the enzyme if the pH increases to 8.
In an enzyme-catalyzed reaction, the substrate binds to the enzyme to form an enzyme-substrate complex. If more substrate is present than enzyme, all of the enzyme binding sites will have substrate bound, and further increases in substrate concentration cannot increase the rate. The activity will decrease; a pH of 6. Learning Objectives To describe how pH, temperature, and the concentration of an enzyme and its substrate influence enzyme activity. Hydrogen Ion Concentration pH Because most enzymes are proteins, they are sensitive to changes in the hydrogen ion concentration or pH.
Summary Initially, an increase in substrate concentration leads to an increase in the rate of an enzyme-catalyzed reaction. Concept Review Exercises The concentration of substrate X is low. What happens to the rate of the enzyme-catalyzed reaction if the concentration of X is doubled? What effect does an increase in the enzyme concentration have on the rate of an enzyme-catalyzed reaction?
Answers If the concentration of the substrate is low, increasing its concentration will increase the rate of the reaction. Trypsin's optimum pH is about 8. If you think about the structure of an enzyme molecule, and the sorts of bonds that it may form with its substrate, it isn't surprising that pH should matter. Suppose an enzyme has an optimum pH around 7.
Imagine that at a pH of around 7, a substrate attaches itself to the enzyme via two ionic bonds. In the diagram below, the groups allowing ionic bonding are caused by the transfer of a hydrogen ion from a -COOH group in the side chain of one amino acid residue to an -NH 2 group in the side chain of another.
In this simplified example, that is equally true in both the substrate and the enzyme. Now think about what happens at a lower pH - in other words under acidic conditions. What you will have will be this:. You no longer have the ability to form ionic bonds between the substrate and the enzyme. If those bonds were necessary to attach the substrate and activate it in some way, then at this lower pH, the enzyme won't work. What if you have a pH higher than 7 - in other words under alkaline conditions.
That leaves. Again, there is no possibility of forming ionic bonds, and so the enzyme probably won't work this time either. At extreme pH's, something more drastic can happen. Remember that the tertiary structure of the protein is in part held together by ionic bonds just like those we've looked at between the enzyme and its substrate.
At very high or very low pH's, these bonds within the enzyme can be disrupted, and it can lose its shape. Introduction to Enzymes Video. Place Order. Introduction to Enzymes The following has been excerpted from a very popular Worthington publication which was originally published in as the Manual of Clinical Enzyme Measurements.
Effects of pH Enzymes are affected by changes in pH. About Us. Contact Us.
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