Question

What general effects would you expect the following changes to have on the rate of an enzyme-catalyzed reaction for an enzyme that has its maximum activity at body temperature (about \(\left.37^{\circ} \mathrm{C} / 310.15 \mathrm{~K}\right)\) ? (a) Lowering the reaction temperature from \(313 \mathrm{~K}\left(40{ }^{\circ} \mathrm{C}\right)\) to \(283 \mathrm{~K}\left(10^{\circ} \mathrm{C}\right)\) (b) Adding a drop of a dilute \(\mathrm{HgCl}_{2}\) solution (c) Adding an oxidizing agent, such as hydrogen peroxide

Short answer

(a) Decrease in reaction rate; (b) Decrease or inhibit reaction rate; (c) Decrease or inhibit reaction rate.

Step-by-step solution

Analyzing Temperature Changes

Enzyme activity is affected by temperature changes. Generally, enzyme-catalyzed reactions increase in rate as temperature increases, up to a point. If the temperature lowers from above the optimum (40°C) to significantly below it (10°C), the reaction rate will decrease. This is because the molecules have less kinetic energy at lower temperatures, resulting in fewer successful collisions and consequently, a slower reaction rate.

Evaluating the Effect of Mercuric Chloride (HgCl₂) Solution

Mercuric chloride ( HgCl₂) is a heavy metal ion that can inhibit enzyme activity by binding to amino acids, particularly cysteine residues, in enzymes. This binding can lead to conformational changes or block active sites, thus reducing the enzyme's activity or completely denaturing the enzyme. Therefore, adding a drop of a dilute HgCl₂ solution is likely to decrease the reaction rate.

Understanding the Effect of an Oxidizing Agent like Hydrogen Peroxide

Oxidizing agents such as hydrogen peroxide can cause the oxidation of side chains or critical groups in the enzyme, potentially leading to changes in enzyme structure or the denaturation of the enzyme. This can significantly affect the enzyme's ability to catalyze reactions, often resulting in a decreased reaction rate or inhibition of the enzyme.

Key concepts

Temperature Effect on Enzymes

Temperature plays a significant role in enzyme activity. Enzymes, being proteins, have an optimal temperature at which they function most efficiently. For human enzymes, this temperature is typically around 37°C (310.15 K). When the temperature is reduced, the kinetic energy of molecules involved in the reaction also decreases.

• This results in fewer collisions between enzyme and substrate molecules, thereby slowing down the rate of reaction.
• As a result, lowering the temperature drastically, like from 40°C to 10°C, significantly reduces enzyme activity because the enzymes are not operating under their optimal conditions.

Enzymatic reactions occur more slowly at lower temperatures, illustrating why organisms often function within a narrow temperature range.

Enzyme Inhibitors

Enzyme inhibitors are substances that can reduce or completely stop enzyme activity. There are different types of inhibitors, but heavy metals like mercuric chloride (HgCl₂) are significant due to their capacity to bind with enzymes.

• Mercuric chloride can interact with enzymes by binding to sulfhydryl groups found on the amino acid cysteine in enzymes.
• Such binding can alter the enzyme's shape, obstruct its active site, diminish its activity, or denature it entirely.

Therefore, introducing a small amount of mercuric chloride into a reaction containing a sensitive enzyme typically decreases the reaction rate, illustrating how potent inhibitors can affect enzymatic processes.

Oxidizing Agents and Enzyme Activity

Oxidizing agents, such as hydrogen peroxide, can significantly impact enzyme activity. These agents can alter the structure and function of enzymes through oxidation.

• Oxidizing agents might modify essential amino acids in the enzyme, disrupting its normal functionality.
• The change in structure can lead to enzyme denaturation, rendering the enzyme unable to facilitate its intended chemical reaction.

By causing such structural changes, oxidizing agents can drastically decrease enzyme activity, highlighting the importance of maintaining specific conditions in biochemical reactions to ensure efficient enzymatic activity.