Question

Which of these statements about enzyme-catalyzed reactions is true? a. The rate of reaction is independent of temperature. b. The rate of all enzyme-catalyzed reactions is decreased when the \(\mathrm{pH}\) is lowered from 7 to 2 . c. The rate of reaction is independent of substrate concentration. d. Under given conditions of substrate concentration, pH, and temperature, the rate of product formation varies directly with enzyme concentration up to a maximum, at which point the rate cannot be increased further.

Short answer

The correct statement about enzyme-catalyzed reactions is: d. Under given conditions of substrate concentration, pH, and temperature, the rate of product formation varies directly with enzyme concentration up to a maximum, at which point the rate cannot be increased further.

Step-by-step solution

Understand enzyme properties

Enzymes are biological catalysts that speed up chemical reactions in cells. They function by lowering the activation energy required for the reaction to proceed, making the reaction more favorable. They do not get used up during the process, meaning that they can catalyze numerous reactions.

Evaluate option A

"The rate of reaction is independent of temperature." Enzymes are proteins, and their activity is affected by temperature. As the temperature increases, the rate of the reaction increases up to an optimal temperature, beyond which the enzyme denatures and its activity decreases. Therefore, this statement is false.

Evaluate option B

"The rate of all enzyme-catalyzed reactions is decreased when the \(\mathrm{pH}\) is lowered from 7 to 2." Enzymes have an optimal pH where they have the highest activity. Outside of this range, their activity can decrease or even become inactive, as the relevant functional groups lose or gain protons, making them less effective. However, it is not universally true that lowering the pH from 7 to 2 will always decrease the rate of all enzyme-catalyzed reactions, as some enzymes work optimally at acidic pH values. Therefore, this statement is false.

Evaluate option C

"The rate of reaction is independent of substrate concentration." The rate of an enzyme-catalyzed reaction depends on substrate concentration up to a certain point. As substrate concentration increases, the reaction rate will increase until it reaches a maximum (Vmax) at which the enzyme becomes saturated, and the rate plateaus. Thus, this statement is false.

Evaluate option D

"Under given conditions of substrate concentration, pH, and temperature, the rate of product formation varies directly with enzyme concentration up to a maximum, at which point the rate cannot be increased further." This statement is accurate because when all other conditions are held constant, increasing the enzyme concentration will increase the rate of the reaction. However, at a certain point (Vmax), all enzyme active sites are working at full capacity, and the reaction rate cannot be further increased. Thus, this statement is true. So, the correct answer is: d. Under given conditions of substrate concentration, pH, and temperature, the rate of product formation varies directly with enzyme concentration up to a maximum, at which point the rate cannot be increased further.

Key concepts

Enzyme Activity

Enzymes are special proteins that act as catalysts in biological processes. They help speed up chemical reactions without being consumed themselves. This means they can be used repeatedly.

The activity of an enzyme depends on several factors, such as temperature and pH. Enzymes are very specific about the conditions they work best in, known as their optimal conditions.

• At the right temperature and pH, they are most active.
• Extreme conditions can denature the enzyme, making it lose its shape and functionality.

Understanding enzyme activity is crucial because it determines how efficiently a biochemical reaction takes place.

Activation Energy

Activation energy is the energy required to start a chemical reaction. Think of it as the initial push needed to start rolling a ball up a hill.

Enzymes play a key role in reducing the activation energy, enabling reactions to occur at a faster rate. They provide an alternative pathway for the reaction with a lower energy requirement.

• This lower energy barrier allows more molecules to have enough energy to undergo the reaction.
• As a result, the rate of the reaction increases.

By lowering the activation energy, enzymes ensure that vital biological reactions can happen efficiently at the normal conditions within the living organism.

Substrate Concentration

Substrate concentration refers to the amount of substrate available for the enzyme to act upon. It is a critical factor influencing enzyme activity.

As the substrate concentration increases, the rate of an enzyme-catalyzed reaction initially increases. This continues until a point of saturation is reached:

• At low substrate concentrations, more substrate makes more active sites occupied, thus, the rate increases.
• Once all enzyme active sites are occupied, adding more substrate will not increase the rate further. This is called saturation.

Understanding how substrate concentration affects enzyme-catalyzed reactions helps in manipulating conditions to achieve desired reaction rates.

Enzyme Saturation

Enzyme saturation occurs when increasing the substrate concentration no longer leads to an increase in reaction rate. This is because all available enzyme active sites are occupied.

This state reflects the maximum rate of reaction, known as Vmax. At this point:

• The enzyme is working at full capacity, and any additional substrate will not be processed faster.
• The reaction velocity plateaus, no matter how much more substrate is added.

Enzyme saturation is important in studying enzyme kinetics, as it provides insight into how enzymes operate under high substrate conditions and helps understand enzyme efficiency and capacity.