Enzyme Function and Regulation: Key Concepts in Biochemistry

Posted on Dec 11, 2024 in Biology

Enzyme

A biomolecule that catalyzes chemical reactions.

Absolute Specificity

The characteristic of an enzyme that it acts on one and only one substance.

Relative Specificity

The characteristic of an enzyme that it acts on several structurally related substances.

Stereochemical Specificity

The characteristic of an enzyme that it is able to distinguish between stereoisomers.

Substrate

The substance that undergoes a chemical change catalyzed by an enzyme.

Inborn Error of Metabolism

A disease in which a genetic change causes a deficiency of a particular protein, often an enzyme.

Cofactor

A nonprotein molecule or ion required by an enzyme for catalytic activity.

Coenzyme

An organic molecule required by an enzyme for catalytic activity.

Apoenzyme

A catalytically inactive protein formed by removal of the cofactor from an active enzyme.

Active Site

The location on an enzyme where a substrate is bound and catalysis occurs.

Lock and Key Theory

A theory of enzyme specificity proposing that a substrate has a shape fitting that of the enzyme’s active site, as a key fits a lock.

Induced Fit Theory

A theory of enzyme action proposing that the conformation of an enzyme changes to accommodate an incoming substrate.

Enzyme Activity

The rate at which an enzyme catalyzes a reaction.

Turnover Number

The number of molecules of substrate acted on by one molecule of enzyme per minute.

Enzyme International Unit (IU)

A quantity of enzyme that catalyzes the conversion of 1 mole of substrate per minute under specified conditions.

Optimum Temperature

The temperature at which enzyme activity is highest.

Optimum pH

The pH at which enzyme activity is highest.

Enzyme Inhibitor

A substance that decreases the activity of an enzyme.

Extremozyme

A nickname for certain enzymes isolated from microorganisms that thrive in extreme environments.

Antibiotic

A substance produced by one microorganism that kills or inhibits the growth of other microorganisms.

Competitive Inhibitor

An inhibitor that competes with substrate for binding at the active site of the enzyme.

Noncompetitive Inhibitor

An inhibitor that binds to the enzyme at a location other than the active site.

Zymogen or Proenzyme

The inactive precursor of an enzyme.

Modulator

A substance that binds to an enzyme at a location other than the active site and alters the catalytic activity.

Allosteric Enzyme

An enzyme with quaternary structure whose activity is changed by the binding of modulators.

Activator

A substance that binds to an allosteric enzyme and increases its activity.

Feedback Inhibition

A process in which the end product of a sequence of enzyme-catalyzed reactions inhibits an earlier step in the process.

Enzyme Induction

The synthesis of an enzyme in response to a cellular need.

Isoenzyme

A slightly different form of the same enzyme produced by different tissues.

What is the Role of Enzymes in the Body?

To catalyze reactions.

List Two Ways that Enzyme Catalysis of a Reaction is Superior to Normal Laboratory Conditions

Allow reactions to achieve equilibrium more rapidly and speed chemical reactions by lowering activation energies.

What is the Relationship Between an Enzyme and the Energy of Activation for a Reaction?

Enzymes lower the energy of activation.

Why are so Many Different Enzymes Needed?

So they only catalyze specific reactions.

List Three Ways in Which Enzymes are Particularly Well Suited for Their Essential Roles in Living Organisms

They have enormous catalytic power.
They are highly specific in the reactions they catalyze.
Their activity as catalysts can be regulated.

What is the Ending of EC Names and Most Common Names of Enzymes?

-ase

What is the Relationship Between Urea and Urease? Between Maltose and Maltase?

Substrate: urea
Enzyme: Urease
Substrate: maltose
Enzyme: Maltase

What are the Relationships Among the Terms Cofactor, Active Enzyme, and Apoenzyme?

Cofactor: nonprotein molecule or ion required by an enzyme for catalytic activity
Active Enzyme: enzyme that is able to perform catalytic activity
Apoenzyme: A catalytically inactive protein formed by removal of the cofactor from an active enzyme

State the Relationship Between Vitamins and Enzyme Activity

Coenzymes are formed in the body by vitamins, so without vitamins, there would be no enzyme activity.

List Some Typical Inorganic Ions that Serve as Cofactors

Mg, Zn, Fe

What Vitamins are Required for FAD and NAD Formation?

NAD: niacin
FAD: riboflavin

In What Way are the Substrate and the Active Site Related?

The active site is the location on an enzyme where the substrate is bound.

Compare Lock and Key Theory with Induced Fit Theory

Lock and key theory proposes that the substrate has a shape that fits the active site of the enzyme, while induced fit proposes that the conformation of the enzyme changes to accommodate an incoming substrate.

List Two Ways of Describing Enzyme Activity

Turnover number and enzyme international unit.

What Observations May be Used in Experiments to Determine Enzyme Activity?

Color, pH

What Happens to the Rate of an Enzyme-Catalyzed Reaction as Substrate Concentration is Raised Beyond the Saturation Point?

It levels out.

How Would You Expect Hypothermia to Affect Enzyme Activity in the Body?

It would lower the reaction rate.

When Handling or Storing Solutions of Enzymes, the pH is Usually Kept Near 7. Why?

Because it is the optimum pH (enzyme activity is highest).

Distinguish Between Irreversible and Reversible Enzyme Inhibition

Irreversible enzyme inhibition forms a covalent bond with a functional group on an enzyme which deactivates it.
Reversible enzyme inhibition reversibly binds to an enzyme; the inhibitor is removed from the enzyme by shifting the equilibrium.

Distinguish Between Competitive and Noncompetitive Enzyme Inhibition

Competitive: compete with substrate for binding at the active site of the enzyme.
Noncompetitive: binds to the enzyme at a location other than the active site.

Why is Regulation of Enzyme Activity Necessary?

So an organism can respond to changing conditions and cellular needs.

List Three Mechanisms for the Control of Enzyme Activity

Activation of zymogens, allosteric regulation, and genetic control.

Describe the Importance of Zymogens in the Body. Give an Example of an Enzyme that has a Zymogen

Zymogens can be stored when not needed and released when needed. Examples: thrombin and zymogen prothrombin; pepsin and pepsinogen.

The Clotting of Blood Occurs by a Series of Zymogen Activations. Why are the Enzymes that Catalyze Blood Clotting Produced as Zymogens?

Because then the blood would constantly clot.

What is Meant by Genetic Control of Enzyme Activity?

Cells increasing the number of enzyme molecules present.

Why are Enzyme Assays of Blood Serum Useful in a Clinical Diagnosis?

Enzyme levels rise when cell damage and destruction occur or during uncontrolled growth.

What are Isoenzymes? Give Two Examples