Enzyme Velocity and Kinetics

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Questions and Answers

What happens to the reaction velocity as substrate concentration increases?

It remains constant regardless of substrate concentration.

It decreases steadily as more substrate is added.

It increases then decreases due to enzyme saturation.

It increases until a maximal velocity is reached. (correct)

How does temperature generally affect enzyme reaction velocity?

The velocity decreases continuously with increasing temperature.

The velocity increases indefinitely with temperature.

The velocity increases until a peak is reached, then it decreases. (correct)

The velocity is not affected by temperature changes.

What characterizes the enzyme kinetics curve for most enzymes?

It is hyperbolic in shape. (correct)

It is sigmoidal in shape.

It is linear across all substrate concentrations.

It shows drastic fluctuations at certain concentrations.

What is the effect of extreme temperatures on human enzymes?

Denaturation starts at temperatures above 40°C. Signup and view all the answers

What distinguishes allosteric enzymes from those that follow Michaelis–Menten kinetics?

They exhibit a sigmoidal reaction velocity curve. Signup and view all the answers

How can elevated substrate concentration affect enzyme activity?

It can lead to saturation and plateau in reaction velocity. Signup and view all the answers

What is the optimal temperature range for most human enzymes?

Between 35°C and 40°C. Signup and view all the answers

What effect does substrate saturation have on enzyme activity?

It leads to a constant rate regardless of additional substrate. Signup and view all the answers

What term describes the protein component of an enzyme along with its nonprotein components?

Holoenzyme Signup and view all the answers

Which of the following is an example of a cofactor?

Zinc (Zn2+) Signup and view all the answers

What is the energy barrier that must be overcome for a reaction to proceed called?

Activation energy (Ea) Signup and view all the answers

Which statement best describes a prosthetic group?

A permanent coenzyme that returns to its original form Signup and view all the answers

What happens to coenzymes during the enzymatic reaction?

They dissociate and are returned to their original form. Signup and view all the answers

Why is compartmentalization of enzymes within cells important?

It isolates substrates from competing reactions. Signup and view all the answers

Which perspective describes how the active site facilitates catalysis?

Chemical environment provided by the active site Signup and view all the answers

What type of nonprotein component is derived from vitamins?

Coenzyme Signup and view all the answers

What role does the active site play in enzyme catalysis?

It stabilizes the transition state to increase reaction speed. Signup and view all the answers

Which type of catalysis involves amino acid residues providing or accepting protons?

General acid-base catalysis Signup and view all the answers

How can the transition state be visualized in an enzyme-catalyzed reaction?

As an uncooperative infant with a sweater. Signup and view all the answers

Which of the following statements about enzymes is correct?

Enzymes have a low activation energy compared to the uncatalyzed reaction. Signup and view all the answers

Which type of catalysis is specifically utilized by chymotrypsin?

General acid, general base, and covalent catalysis Signup and view all the answers

What affects the probability of the transition state being formed during a reaction?

The stability of the enzyme-substrate complex Signup and view all the answers

Which factor is not typically mentioned as affecting enzyme activity?

Turbulence in surrounding liquid Signup and view all the answers

What happens to the energy of the substrate when it binds to the enzyme?

It decreases slightly. Signup and view all the answers

Study Notes

Enzyme Velocity

The rate or velocity (v) of an enzyme-catalyzed reaction is the number of substrate molecules converted into product per unit time, typically measured in μmol of product formed per second.
Reaction velocity increases with substrate concentration until a maximal velocity (Vmax) is reached, indicating saturation of all available binding sites on the enzyme molecules.
Most enzymes follow Michaelis–Menten kinetics, resulting in a hyperbolic plot of initial reaction velocity (vo) against substrate concentration.
Allosteric enzymes, however, do not follow Michaelis–Menten kinetics, exhibiting a sigmoidal curve instead.

Temperature and Enzyme Velocity

Reaction velocity increases with temperature until a peak velocity is reached, due to increased substrate molecule energy overcoming the energy barrier.
Further temperature elevation causes a decrease in reaction velocity due to temperature-induced enzyme denaturation.
Human enzymes have an optimum temperature between 35° and 40°C, while thermophilic bacteria found in hot springs have optimum temperatures of 70°C.

Enzyme Components and Structure

Some enzymes require nonprotein components for activity, including metal ions (cofactors) and small organic molecules (coenzymes).
The complete enzyme with its nonprotein component is called a holoenzyme, while the enzyme without its nonprotein moiety is termed an apoenzyme and is inactive.
Coenzymes can be permanently (prosthetic groups) or transiently associated with an enzyme.
Coenzymes are often derived from vitamins, like NAD+ containing niacin, and FAD containing riboflavin.

Enzyme Regulation

Enzyme activity can be increased or decreased to respond to cellular needs.

Enzyme Location

Most enzymes function within cells, confined by plasma membranes.
Many enzymes are localized within specific organelles, facilitating compartmentalization and organized metabolic pathways.

Enzyme Action: Energy Changes

Chemical reactions have an energy barrier separating reactants and products, called the activation energy (Ea).
Enzymes lower the activation energy by stabilizing the transition state, accelerating the reaction.

Enzyme Action: Active Site Catalysis

The active site of an enzyme provides catalytic groups that enhance transition state formation.
Catalytic groups can participate in general acid–base catalysis, providing or accepting protons.
Covalent catalysis can also occur, forming a transient covalent ES complex.
Chymotrypsin, an enzyme of protein digestion, exemplifies general base, general acid, and covalent catalysis, involving histidine and serine residues at its active site.

Enzyme Action: Transition State Visualization

The conversion of substrate to product can be visualized as removing a "sweater" (chemical group) from an "infant" (substrate).
Enzymes act as "parents," guiding the substrate into a transition state conformation that facilitates product formation.

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Description

Explore the principles of enzyme velocity in this quiz, which covers the basics of reaction rates, Michaelis–Menten kinetics, and the effects of temperature on enzyme activity. Understand how substrate concentration and temperature influence the efficiency of enzymes in biological reactions.