Question

REFLECT AND APPLY 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 denatures enzymes, reducing their activity. High substrate concentrations protect the enzyme, lessening the activity decrease.

Step-by-step solution

Understand Enzyme Activity

Enzymes are biological catalysts that speed up chemical reactions. Their activity depends on their three-dimensional structure, which can be easily disrupted by changes in environmental conditions such as temperature.

Explain Effect of Heating without Substrate

When the solution containing an enzyme is heated significantly, the heat can denature the enzyme. Denaturation involves the unraveling of the enzyme's three-dimensional structure, making it ineffective in catalyzing reactions.

Explain Effect of Heating with High Substrate Concentrations

The presence of a high concentration of substrate can stabilize the enzyme's structure, providing some degree of protection against denaturation due to heat. This stabilization occurs because the substrate molecules bind to the active sites of the enzyme, shielding these sites and helping to maintain their proper shape.

Conclusion

Heating an enzyme solution decreases enzyme activity because it denatures the enzyme. However, high substrate concentrations can help protect the enzyme from heat denaturation, resulting in a less marked decrease in activity.

Key concepts

enzyme activity

Enzyme activity is a measure of the rate at which an enzyme catalyzes a reaction. Enzymes are proteins that act as biological catalysts, meaning they speed up chemical reactions in the body without being consumed.

• The efficiency of enzymes depends on their unique three-dimensional structure.
• Changes in temperature, pH, and other environmental factors can affect enzyme activity.

When an enzyme's structure is intact, it can effectively bind to its substrate — the molecule it acts upon — and catalyze a specific reaction. Any alteration in the enzyme's structure can reduce its activity, making it less efficient or completely inactive.

denaturation

Denaturation refers to the process in which an enzyme loses its native three-dimensional structure. This can be caused by extreme environmental conditions, such as very high temperatures.

• Denatured enzymes have their active sites altered or destroyed, which prevents substrate binding and reaction catalysis.
• Heat is a common cause of denaturation as it can cause proteins to unfold and lose their functional shape.

When an enzyme denatures, it becomes ineffective. This is because the specific shape of the enzyme, especially around the active site, is essential for binding to its substrate and facilitating the reaction. Without this precise structure, the enzyme cannot perform its function.

substrate concentration

Substrate concentration refers to the amount of substrate present in a solution that an enzyme reacts with. The concentration of substrates can influence enzyme activity significantly.

• Higher substrate concentrations generally increase the rate of reaction up to a point where the enzyme is saturated.
• Beyond saturation, additional substrate molecules do not further increase the reaction rate.

High substrate concentrations can also stabilize enzymes against denaturation. This happens because substrate molecules can bind to the active sites of the enzyme, helping maintain its proper structure even in adverse conditions such as high temperatures.

thermal stability

Thermal stability refers to an enzyme's ability to remain functional at elevated temperatures. Some enzymes are more thermally stable than others due to their molecular structure.

• Enzymes with higher thermal stability can withstand higher temperatures without denaturing.
• Thermal stability is crucial for enzymes to function in environments with variable temperatures.

The presence of substrates can improve thermal stability. When substrates bind to an enzyme, they can provide a protective effect, lowering the likelihood of denaturation by stabilizing the enzyme’s structure. This is why enzyme activity decreases less markedly in high substrate concentrations even when the temperature is increased.