Enzyme Active Site

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Questions and Answers

What is the slope of the Lineweaver-Burk plot?

Km/Vmax^2

Km/Vmax (correct)

1/Vmax

Vmax/Km

What is the y-intercept of the Lineweaver-Burk plot?

Vmax/Km

1/Km

Km/Vmax

1/Vmax (correct)

Which of the following factors affects enzyme activity?

Substrate concentration and enzyme concentration

Substrate concentration, enzyme concentration, and temperature

Temperature, pH, and activators

All of the above (correct)

What happens to the rate of reaction when the substrate concentration increases to a certain point?

The rate of reaction reaches a maximum and then plateaus Signup and view all the answers

What is the advantage of the Lineweaver-Burk plot?

All of the above Signup and view all the answers

What is the primary function of the International Union of Biochemistry in relation to enzymes?

To establish a systematic nomenclature for enzymes Signup and view all the answers

What is the significance of the Michaelis constant (Km) in enzyme kinetics?

It is a measure of the enzyme's affinity for the substrate Signup and view all the answers

What is the effect of increasing enzyme concentration on the rate of reaction?

The rate of reaction increases Signup and view all the answers

What is the effect of temperature on enzyme activity?

Temperature has an optimal range for enzyme activity Signup and view all the answers

What is the purpose of the Enzyme Commission?

To establish a systematic nomenclature for enzymes Signup and view all the answers

What is the effect of pH on enzyme activity?

pH has an optimal range for enzyme activity Signup and view all the answers

What is the relationship between [S] and Vo in the Michaelis-Menten model?

Hyperbolic Signup and view all the answers

What is the significance of Vmax in the Michaelis-Menten equation?

It represents the maximum reaction velocity Signup and view all the answers

What is the correct sequence of events in the Michaelis-Menten model?

E combines with S to form ES, then ES breaks down to form E and P Signup and view all the answers

What is the purpose of the systematic name of an enzyme, according to the IUB system?

To describe the enzyme's function and substrate Signup and view all the answers

How are enzymes classified, according to the IUB system?

Based on the reaction they catalyze Signup and view all the answers

What is the primary function of the active site in an enzyme?

To provide a site for substrate binding and catalysis Signup and view all the answers

Which of the following theories describes the highly specific binding of substrate to an enzyme's active site?

Lock and Key Theory Signup and view all the answers

How do enzymes lower the activation energy needed for a reaction to occur?

By providing an alternative reaction pathway Signup and view all the answers

What is the role of metal ions in enzyme catalysis?

To coordinate charge stabilization Signup and view all the answers

Which of the following mechanisms of enzyme catalysis involves the formation of a transient covalent bond?

Covalent catalysis Signup and view all the answers

How are enzymes typically named?

By adding the suffix 'ase' to the name of the substrate Signup and view all the answers

Which of the following enzymes is an exception to the 'ase' naming convention?

Trypsin Signup and view all the answers

What is the result of the binding of substrate to an enzyme's active site?

A change in the shape of the enzyme to enhance binding Signup and view all the answers

What is the effect of a competitive inhibitor on the Km of an enzyme?

Increased Signup and view all the answers

Which type of inhibitor binds to the active site of an enzyme?

Competitive inhibitor Signup and view all the answers

What is the effect of a non-competitive inhibitor on the Vmax of an enzyme?

Decreased Signup and view all the answers

What is the effect of increasing the substrate concentration on a competitive inhibitor?

Overcome the inhibition Signup and view all the answers

What is the characteristic of an isozyme?

Different amino acid sequence Signup and view all the answers

What is the effect of a non-competitive inhibitor on the Km of an enzyme?

Unchanged Signup and view all the answers

What is the characteristic of a non-competitive inhibitor?

Binds to an allosteric site Signup and view all the answers

What is the X-intercept of the curve in the presence of a non-competitive inhibitor?

Unchanged Signup and view all the answers

What happens to the rate of reaction when the enzyme concentration is doubled at all substrate concentrations?

The rate of reaction doubles Signup and view all the answers

What is the effect of increasing the substrate amount on the rate of reaction beyond a certain point?

The rate of reaction no longer increases Signup and view all the answers

What is the definition of 1 unit of enzyme activity?

The amount of enzyme causing transformation of 1.0 micromole of substrate per minute Signup and view all the answers

What is the effect of irreversible inhibitors on enzyme activity?

They bind covalently to the enzyme molecule and destroy enzyme function Signup and view all the answers

What is the purpose of many drugs that work by inhibiting enzyme activity?

To decrease the enzyme activity Signup and view all the answers

What is the difference between reversible and irreversible inhibitors?

Reversible inhibitors bind weakly, while irreversible inhibitors bind covalently Signup and view all the answers

Study Notes

The Active Site

The active site is the place in the enzyme structure where the reaction occurs.
Active sites are usually clefts or crevices in the protein where the substrate binds by multiple weak bonds.
There are two theories that describe the substrate binding to an enzyme's active site: the Lock and Key Theory and the Induced Fit Theory.
The Lock and Key Theory states that the active site is highly specific, and only molecules with a complementary shape can bind.
The Induced Fit Theory states that the binding of the substrate often results in changes in the shape of the enzyme to enhance binding.

How Enzymes Work

Enzymes work by lowering the activation energy needed for a reaction to occur.
Enzymes employ multiple mechanisms to facilitate catalysis, including:
- Covalent catalysis: formation of a transient covalent bond between a substrate and a residue in the enzyme active site or with a cofactor.
- Metal ion catalysis: a metal ion in the active site participates in catalysis by coordinating charge stabilization.
- Catalysis by proximity or strain: an enzyme can accelerate a reaction between two species simply by holding the two reactants close together in an appropriate orientation.
- Acid-base catalysis: involves conformational change due to change in pH, so some ionic bond is broken or formed.

Enzyme Nomenclature

Enzymes are named by adding the suffix "ase" to the name of the substrate.
Systematic Name: IUB System, consists of two parts: the name of the substrate and the type of reaction (ending in -ase).

Enzyme Classification

Enzymes are classified into six different groups according to the reaction being catalyzed.
Each enzyme has a unique EC number that identifies it.

The Michaelis-Menten Model

The Michaelis-Menten Model describes the kinetics of enzyme-catalyzed reactions.
The model assumes that an enzyme, E, combines reversibly with a substrate, S, to form an enzyme-substrate intermediate, ES.
The relationship between [S] and V0 has a hyperbolic shape, which can be expressed algebraically by the Michaelis-Menten equation.

The Lineweaver-Burk Plot

The Lineweaver-Burk plot is a graphical representation of the Michaelis-Menten equation.
The plot is a straight line with a slope of Km/Vmax and a y-intercept of 1/Vmax.
The Lineweaver-Burk plot is useful for determining the kinetic parameters Km and Vmax.

Factors Affecting Enzyme Activity

Substrate concentration: increasing substrate concentration increases the rate of reaction, but only up to a certain point.
Enzyme concentration: the rate of reaction is directly proportional to the enzyme concentration.
Temperature: affects the rate of reaction, with an optimal temperature for enzyme activity.
pH: affects the rate of reaction, with an optimal pH for enzyme activity.
Activators and inhibitors: can increase or decrease the rate of reaction, respectively.

Inhibition of Enzyme Activity

Inhibition can be reversible or irreversible.
Reversible inhibition can be competitive or non-competitive.
Competitive inhibitors compete with the substrate for binding at the active site.
Non-competitive inhibitors bind at a site other than the active site.

Isozymes

Isozymes are enzymes that differ in amino acid sequence but catalyze the same chemical reaction.

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Description

This quiz covers the concept of active site in enzymes, including the Lock and Key Theory and the Induced Fit Theory, and how they facilitate biochemical reactions.