Question

Suggest a reason why heating a solution containing an enzyme markedly decreases its activity. Why is the decrease of activity frequently much less when the solution contains high concentrations of the substrate?

Short answer

Heating causes enzyme denaturation, reducing activity. High substrate concentrations stabilize the enzyme, partially protecting it from heat.

Step-by-step solution

Understand Enzyme Structure

Enzymes are proteins that have a specific three-dimensional structure necessary for their function. The active site of an enzyme, where the substrate binds, is highly dependent on this precise shape.

Effect of Heat on Protein Structure

Heating can cause denaturation, which means that the enzyme's three-dimensional structure unfolds. This structural change can negatively impact the active site, rendering the enzyme less effective or inactive.

Substrate Concentration Protective Effect

When there is a high concentration of substrate, it can help stabilize the enzyme structure. The substrate binding helps maintain the enzyme's shape, even under slightly elevated temperatures, thereby decreasing the rate of denaturation.

Combine the Concepts

Summarize that heating an enzyme solution decreases enzyme activity due to denaturation. However, high substrate concentrations can partially protect the enzyme by stabilizing its structure, leading to a lesser decrease in activity.

Key concepts

enzyme structure

Enzymes are biological molecules that speed up chemical reactions in living organisms. They are proteins, and their function is highly dependent on their unique three-dimensional structure. This complex structure includes an active site.
The active site is a specific region on the enzyme where the substrate—the molecule upon which the enzyme acts—binds. This binding occurs in a highly specific manner, like a key fitting into a lock. The enzyme's shape is thus critical to its function.
If this shape is altered, the enzyme may no longer function correctly. This concept is fundamental to understanding how enzymes work and why certain conditions can affect their activity.

effect of heat on protein

Heat can have a significant effect on enzymes, as they are proteins. When proteins are exposed to heat, they can undergo a process known as denaturation.
Denaturation involves the unfolding of the protein's three-dimensional structure. As the structure unravels, the precise shape of the active site can be lost.
When the active site is altered, the substrate may no longer fit, or the enzyme may be unable to catalyze reactions effectively. This is why heating a solution containing an enzyme markedly decreases its activity.
The extent of denaturation and loss of activity depends on several factors, including the temperature and duration of the heat exposure.

substrate concentration

Substrate concentration can influence the stability and activity of enzymes under heat stress. When an enzyme solution contains a high concentration of substrate, the substrate molecules can help stabilize the enzyme's structure.
This stabilization occurs because the binding of substrates to the enzyme can help maintain the enzyme's proper shape, even at elevated temperatures.
As a result, the rate of denaturation can be reduced, and the enzyme may retain more of its activity compared to a situation where substrate concentration is low.
This protective effect highlights the importance of substrate presence in preserving enzyme function under potentially denaturing conditions.