Video Transcript
Enzymes have an optimum temperature. Which of the following best defines the term “optimum temperature”? (A) The optimum temperature is the temperature at which the enzyme functions best. (B) The optimum temperature is the temperature at which the rate of reaction is the slowest. (C) The optimum temperature is the temperature at which the enzyme denatures. (D) The optimum temperature is the temperature at which the enzyme catalyzes the largest number of different reactions. Or (E) the optimum temperature is the temperature at which the enzyme can replicate.
To understand about the optimum temperature for an enzyme, let’s first review the key facts about how enzymes work. Enzymes are biological catalysts that speed up chemical reactions without being used up themselves. They are made of folded polypeptides and have specific shapes, determined by the order of the amino acids along the chain. These amino acids form bonds with each other, which helps establish their overall shape and, most importantly, the shape of the active site.
The active site is the area of the enzyme that binds with the substrate. It is complementary to the substrate and so they fit together perfectly, forming an enzyme–substrate complex. The reaction can now take place and the products are released. Because the active site is specific to just one substrate, an enzyme can only catalyze one particular reaction.
Now, let’s look at what is meant by the optimum temperature for an enzyme. How well an enzyme catalyzes a reaction can be affected by changes in the environment, such as temperature. The binding of the enzyme and substrate relies on the two molecules bumping into each other. At low temperatures, molecules have very little kinetic energy. So they move around slowly and are less likely to bump into each other, so reaction rate is low.
This can be shown on a graph. The rate of reaction is indicated on the 𝑦-axis. You can see here that as temperature increases, the reaction rate increases. This is because the kinetic energy of the molecules increases, and so there are more successful collisions. This continues until the maximum rate is reached, again shown on the graph. This is known as the optimum temperature. As the temperature continues to increase further, the bonds holding the enzyme structure together start to break down. The active site starts to change shape. And eventually, the reaction stops, because the substrate molecules can no longer bind with the enzyme. The enzyme is now said to be denatured.
We can now return to the question and try to find the answer that best describes “optimum temperature.” From what we have learned, we know that optimum temperature refers to the temperature at which an enzyme will function at its best. Options (A) and (D) both look like they could be correct. However, option (D) refers to “different reactions.” And an enzyme can only catalyze one specific reaction because of its active site that binds with a specific substrate. (D) is therefore incorrect.
So, the correct answer is (A). The optimum temperature is the temperature at which the enzyme functions best.
