Taq polymerase is an enzyme found in bacteria that live in hot springs. Its optimum temperature is 75 to 80 degrees Celsius. Which graph best displays how the activity of Taq polymerase changes with
In order to decide which of the four graphs is the correct one, we need to understand
how to interpret a graph showing how the rate of an enzyme-controlled reaction
varies with temperature.
Let’s first have a look at an example of a graph for an enzyme we will call X. The pink line indicates the relationship between temperature and rate of
reaction. It starts at a temperature of zero degrees Celsius. At this temperature, the reaction is not occurring, so there is a rate of zero. As temperature increases, the kinetic energy contained within the substrate and
enzyme molecules increases. The increased energy makes the molecules move faster. And the substrate molecules are more likely to collide successfully with the enzyme
molecules’ active sites. Therefore, as the temperature rises, the rate of reaction increases. So the line on the graph goes upwards.
The optimum temperature is the temperature at which that specific enzyme functions at
its best. It is the temperature at which the enzyme’s rate of reaction is the highest. On this specific graph, it will be the point where the line reaches a peak at 30
degrees Celsius, indicated by the green circle. At temperatures above the optimum, we see the pink line descending as the rate of
The conditions are now not so favorable for the enzyme. The active site begins to change shape so that it is no longer complementary to the
shape of its specific substrate molecule. We say that the enzyme is becoming denatured. This change is irreversible. It means that the enzyme will no longer be able to catalyze the reaction. So the rate of reaction will eventually decrease to zero.
Now let’s apply what we have learnt to try and answer our question. We are told in the question that the optimum temperature for Taq polymerase is 75 to
80 degrees Celsius. If we draw a dotted line from each peak straight down to the 𝑥-axis, we can
establish the optimum temperature. We can now see that the graph with the peak closest to 75 to 80 degrees Celsius is