Enzyme Kinetics

What defines a first-order reaction in terms of reaction velocity?

A first-order reaction is one where the reaction velocity is directly proportional to the concentration of one reactant.

What are the units of the proportionality constant (k) in first-order reactions?

The units of k for first-order reactions are s−1.

How can metabolic pathways be illustrated to show enzyme functions and interactions?

Metabolic pathways are illustrated using flow diagrams that depict substrate transformations and enzyme interactions step-by-step.

What is the threshold effect in the context of allosteric enzyme activity?

The threshold effect refers to the heightened sensitivity of allosteric enzymes to changes in substrate concentration around their Kₘ values.

How is catalytic efficiency measured using kcat/Kₘ?

Catalytic efficiency is measured by the ratio kcat/Kₘ, which reflects how effectively an enzyme converts substrate to product.

How can you determine Kₘ from the Michaelis-Menten equation?

Kₘ can be determined at the point where V₀ equals half of Vmax, which corresponds to substrate concentration.

Describe a method for measuring the effect of regulatory molecules on enzyme kinetics.

Regulatory effects can be measured by comparing reaction velocities in the presence and absence of the regulatory molecules under identical conditions.

How do activators influence the activity of allosteric enzymes?

Activators stabilize the R state, increasing enzyme activity and enhancing the conversion of substrate to product.

What are the units of the proportionality constant for second-order reactions?

The units of the proportionality constant for second-order reactions are M−1 s−1.

How can one study the activity of individual enzyme molecules?

Individual enzyme molecules can be studied using techniques that isolate them and measure their activity under controlled conditions.

What is the concerted model in relation to allosteric enzyme regulation?

The concerted model suggests that allosteric enzymes exist in two states (T and R) and that substrate binding stabilizes the R state.

What are the implications of a loss of allosteric regulation in enzymes, such as in the case of phosphoribosylpyrophosphate synthetase?

Loss of allosteric regulation can lead to overproduction of metabolites, resulting in diseases like gout.

Why are Kₘ and Vmax important characteristics of enzymes?

Kₘ indicates the affinity of an enzyme for its substrate, while Vmax represents the maximum reaction rate.

What is the relationship between substrate concentration and initial velocity in enzyme kinetics?

Initial velocity increases as substrate concentration increases, showing a hyperbolic or sigmoidal relationship.

What is the role of allosteric enzymes in metabolic pathways?

Allosteric enzymes regulate the flow of biochemical reactions, ensuring proper metabolic control and efficiency.

What does a high kcat/Kₘ ratio indicate about an enzyme's performance?

A high kcat/Kₘ ratio suggests that the enzyme has high catalytic efficiency and approaches diffusion-controlled limits.

How do Kₘ values typically relate to substrate concentration in vivo?

Kₘ values are often approximately equal to the substrate concentration of the enzyme in vivo.

What is the turnover number (kcat) and why is it significant?

kcat is the number of substrate molecules converted to product per second, indicating enzyme efficiency.

How is the Lineweaver-Burk equation related to the Michaelis-Menten model?

The Lineweaver-Burk equation linearizes the Michaelis-Menten equation, allowing for easier determination of Kₘ and Vmax.

What occurs to the T ⇌ R equilibrium when an inhibitor binds to an allosteric enzyme?

Inhibitors stabilize the T state, shifting the equilibrium towards the less active form and reducing activity.

How does the binding of substrate to an allosteric enzyme affect its conformation?

Substrate binding to one active site influences the conformation of other active sites, promoting the R state and enhancing activity.

What is the Michaelis-Menten model and its significance in enzyme kinetics?

The Michaelis-Menten model describes how enzyme reaction velocity is affected by substrate concentration, helping characterize enzyme activity.

What factors can contribute to the equilibrium of different conformations in enzymes?

Factors include substrate concentration, presence of inhibitors or activators, and innate structural properties of the enzyme.

How does a second-order reaction differ from a first-order reaction?

In a second-order reaction, the reaction velocity depends on the concentrations of two reactants or the square of one reactant's concentration.

How do allosteric enzymes differ from Michaelis-Menten enzymes in terms of kinetics?

Allosteric enzymes display a sigmoidal relationship with substrate concentration, unlike the hyperbolic relationship of Michaelis-Menten enzymes.

What does it mean when V₀ = ½ Vmax?

This indicates that the substrate concentration equals Kₘ, representing the half-saturation point of the enzyme.

Describe the characteristics of sequential and double-displacement reactions.

Sequential reactions form a ternary complex of two substrates and an enzyme, while double-displacement reactions involve a substituted enzyme intermediate (ping-pong mechanism).

How is the initial velocity (V₀) of an enzyme-catalyzed reaction measured?

V₀ is measured by determining product formation over time shortly after the reaction starts.

What is feedback inhibition and how does it regulate allosteric enzymes?

Feedback inhibition occurs when the end product of a pathway inhibits an enzyme earlier in the pathway, regulating flux.

What is reaction velocity and how is it calculated?

Reaction velocity is the rate at which reactants disappear or products appear, calculated as the change in concentration over time.