Kinetics and Regulation

These flashcards cover key concepts related to enzyme kinetics and regulation, including definitions, mechanisms, and physiological significance.

Enzyme Kinetics

The study of the rates of enzyme-catalyzed reactions.

Michaelis-Menten Equation

Describes the variation of enzyme activity as a function of substrate concentration, where KM is a key parameter.

Initial Velocity (V0)

The number of moles of product formed per second shortly after the reaction has begun.

Vmax

The maximal velocity attainable when all enzyme is bound to substrate.

KM (Michaelis constant)

A measure of the substrate concentration required for significant catalysis; unique to each enzyme.

Allosteric Enzymes

Enzymes that regulate the flux of biochemicals through metabolic pathways and respond to environmental signals.

Feedback Inhibition

A regulatory mechanism in which a product of a pathway inhibits an upstream process to control pathway flow.

Rate Constant (k)

A proportionality constant that relates the reaction velocity to substrate concentration.

Turnover Number (kcat)

The number of substrate molecules that an enzyme can convert into product per unit time when saturated.

Elasticity

The sensitivity of an enzyme's activity to changes in environmental conditions and substrate concentrations.

Bisubstrate Reactions

Reactions that involve two substrates and produce two products.

Sequential Reactions

Reactions where all substrates must bind to the enzyme before any product is released.

Double-Displacement Reaction

A reaction where one or more products are released before all substrates bind the enzyme.

Concerted Model

Describes allosteric enzyme behavior where all active sites are in the same state, either tense or relaxed.

Cooperativity

The phenomenon where the binding of substrate to one active site affects the activity of other active sites.

Single-Molecule Experiments

Experiments that allow observation of an individual enzyme molecule to study its unique behavior.

Ensemble Studies

Experiments performed on a buffered solution containing millions of enzyme molecules, assuming homogeneity.

Heterotropic Effects

When the binding of one molecule affects the binding of a different molecule to an enzyme.

Homotropic Effects

When the binding of one molecule affects the binding of additional identical molecules to an enzyme.

Physiological Significance of KM

The sensitivity of an enzyme's activity to substrate concentration relates to its KM value.

Enzyme Kinetics

The study of the rates of enzyme-catalyzed reactions.

Michaelis-Menten Equation

Describes the variation of enzyme activity as a function of substrate concentration, where KM is a key parameter.

Michaelis-Menten Equation Formula

$V<em>0 = \frac{V</em>{max}[S]}{K<em>M + [S]}$, where $V</em>0$ is the initial velocity, $V<em>{max}$ is the maximal velocity, $[S]$ is the substrate concentration, and $K</em>M$ is the Michaelis constant.

Initial Velocity (V0)

The number of moles of product formed per second shortly after the reaction has begun.

Rationale for Initial Velocity Measurement

$V_0$ is measured early in the reaction to ensure that the substrate concentration has not significantly decreased and that product concentration is too low to cause product inhibition or reverse reactions.

Vmax

The maximal velocity attainable when all enzyme is bound to substrate.

KM (Michaelis constant)

A measure of the substrate concentration required for significant catalysis; unique to each enzyme.

What does a low $K_M$ value indicate for an enzyme?

A low $K_M$ indicates a high affinity of the enzyme for its substrate, meaning the enzyme can achieve significant catalysis at lower substrate concentrations.

Allosteric Enzymes

Enzymes that regulate the flux of biochemicals through metabolic pathways and respond to environmental signals.

What type of kinetics plot is characteristic of allosteric enzymes?

Allosteric enzymes typically exhibit a sigmoidal (S-shaped) plot of reaction velocity versus substrate concentration, indicating cooperativity.

Feedback Inhibition

A regulatory mechanism in which a product of a pathway inhibits an upstream process to control pathway flow.

Rate Constant (k)

A proportionality constant that relates the reaction velocity to substrate concentration.

Turnover Number (kcat)

The number of substrate molecules that an enzyme can convert into product per unit time when saturated.

How is the turnover number ($k<em>{cat}$) calculated from $V</em>{max}$?

$k<em>{cat} = \frac{V</em>{max}}{[E]<em>T}$, where $[E]</em>T$ is the total enzyme concentration. This represents the number of substrate molecules converted to product per enzyme molecule per second when saturated.

Elasticity

The sensitivity of an enzyme's activity to changes in environmental conditions and substrate concentrations.

Bisubstrate Reactions

Reactions that involve two substrates and produce two products.

Sequential Reactions

Reactions where all substrates must bind to the enzyme before any product is released.

What are the two main types of Sequential Bisubstrate Reactions?

1. Ordered: Substrates bind in a specific sequence (e.g., A then B).
2. Random: Either substrate can bind first, followed by the other.

Double-Displacement Reaction

A reaction where one or more products are released before all substrates bind the enzyme.

What is another name for a Double-Displacement reaction mechanism?

It is also known as a Ping-Pong mechanism, where a product is released, and the enzyme is modified (often by covalently binding part of a substrate) before the second substrate binds.

Concerted Model

Describes allosteric enzyme behavior where all active sites are in the same state, either tense or relaxed.

Cooperativity

The phenomenon where the binding of substrate to one active site affects the activity of other active sites.

Single-Molecule Experiments

Experiments that allow observation of an individual enzyme molecule to study its unique behavior.

Ensemble Studies

Experiments performed on a buffered solution containing millions of enzyme molecules, assuming homogeneity.

Heterotropic Effects

When the binding of one molecule affects the binding of a different molecule to an enzyme.

Homotropic Effects

When the binding of one molecule affects the binding of additional identical molecules to an enzyme.

Physiological Significance of KM

The sensitivity of an enzyme's activity to substrate concentration relates to its KM value.