Enzymes Overview and Functions

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Questions and Answers

What effect does noncompetitive inhibition have on Vmax and Km?

Vmax decreases; Km increases

Vmax unchanged; Km decreases

Vmax decreases; Km unchanged (correct)

Vmax stays the same; Km increases

How does uncompetitive inhibition affect Km and Vmax?

Vmax is unchanged; Km is unchanged

Vmax decreases; Km is unchanged

Vmax decreases; Km appears decreased (correct)

Vmax increases; Km remains unchanged

What is required for uncompetitive inhibition to occur?

Competition with a noncompetitive inhibitor

Formation of an ES complex (correct)

Presence of excess substrate only

Binding of the inhibitor alone to the enzyme

How does a mixed inhibitor affect Km and Vmax?

Vmax decreases; Km may decrease or increase Signup and view all the answers

What is a common method for measuring enzyme activity?

Photometrically measuring absorbance changes Signup and view all the answers

Under what conditions are enzyme concentrations performed?

In zero-order kinetics with excess substrate Signup and view all the answers

Which coenzyme is frequently measured in enzymatic reactions?

NADH Signup and view all the answers

What is the significance of keeping any coenzymes in excess during enzyme activity measurement?

To maintain linearity in reaction kinetics Signup and view all the answers

What role do enzymes play in physiologic reactions?

They facilitate reactions by lowering the activation energy. Signup and view all the answers

What is indicated by the binding of a substrate to the active site of an enzyme?

Formation of the enzyme-substrate (ES) complex. Signup and view all the answers

What type of specificity do enzymes exhibit when they bind only to one type of substrate?

Absolute specificity. Signup and view all the answers

What effect does substrate concentration have on enzymatic reactions?

It can speed up the reaction until saturation is reached. Signup and view all the answers

Which statement is true regarding the transition state of the enzyme-substrate complex?

It has a lower energy of activation than that of the substrate alone. Signup and view all the answers

What occurs when an enzyme has bonding specificity?

It binds only to specific chemical bonds. Signup and view all the answers

In cooperative binding, what happens when one substrate molecule binds to the enzyme?

It facilitates the binding of additional substrate molecules. Signup and view all the answers

How does enzyme catalysis affect the equilibrium of a chemical reaction?

It lowers the activation energy for both forward and reverse reactions. Signup and view all the answers

What is a key advantage of continuous monitoring of enzyme reactions over fixed-time methods?

It allows for multiple data points to confirm linearity. Signup and view all the answers

What typically indicates a deviation from linearity in enzyme reactions?

When substrate is fully consumed early in the reaction. Signup and view all the answers

What happens if a sudden decrease in the reaction rate is observed during continuous monitoring?

The determination may be repeated with less patient sample. Signup and view all the answers

What is the international unit (IU) defined as?

The amount of enzyme that catalyzes 1 μmol of substrate per minute. Signup and view all the answers

Which factor does NOT compromise enzyme activity measurements?

Presence of necessary cofactors. Signup and view all the answers

Which of the following factors can alter enzyme activity results?

Temperature. Signup and view all the answers

Why might reference values for enzyme activity differ among laboratories?

Variations in specified conditions across labs. Signup and view all the answers

What is the SI unit of enzyme activity recognized internationally?

Katal (mol/s). Signup and view all the answers

What role do enzymes play in catalyzing reactions related to ATP?

They catalyze the joining of two substrate molecules. Signup and view all the answers

What do the second and third digits of the EC code represent?

The subclass and sub-subclass of the enzyme. Signup and view all the answers

What is required for a chemical reaction to proceed towards product formation?

Sufficient kinetic energy in reactants. Signup and view all the answers

What does activation energy refer to in the context of chemical reactions?

Energy required to raise reactants to the transition state. Signup and view all the answers

How can one increase the energy of a chemical reaction to facilitate product formation?

By increasing the temperature. Signup and view all the answers

What ultimately happens to reactants that possess enough energy to overcome the energy barrier?

They participate in product formation. Signup and view all the answers

What does the final number in the EC code indicate?

The serial number specific to each enzyme in its sub-subclass. Signup and view all the answers

Which of the following statements best describes the transition state in a chemical reaction?

It is a point where molecules have an equal chance to react or remain unreacted. Signup and view all the answers

What happens to the reaction rate as substrate concentration increases at low levels?

The reaction rate steadily increases. Signup and view all the answers

What characterizes first-order kinetics in enzymatic reactions?

Reaction rate is proportional to substrate concentration. Signup and view all the answers

What does the Michaelis-Menten constant (Km) represent?

The substrate concentration at which reaction velocity is half of the maximum. Signup and view all the answers

What is true about zero-order kinetics within enzymatic reactions?

The reaction velocity does not change with varying substrate concentration. Signup and view all the answers

What is indicated by a high Km value for an enzyme-substrate pair?

Higher substrate concentration is needed to reach half-max velocity. Signup and view all the answers

What condition is assumed about the equilibrium in the Michaelis-Menten model?

Equilibrium among E, S, ES, and P is established rapidly. Signup and view all the answers

Which part of the equation V = (Vmax[S])/(Km + [S]) represents the maximum velocity (Vmax) of the reaction?

Vmax is reached when the substrate concentration saturates the enzyme. Signup and view all the answers

When is the reaction considered to be at maximum velocity?

When all available enzyme molecules are occupied by substrate. Signup and view all the answers

What is the purpose of a Lineweaver-Burk plot?

To obtain a straight line representation of the Michaelis-Menten constant Signup and view all the answers

What happens to enzyme activity when the substrate concentration exceeds the enzyme concentration?

The reaction velocity becomes proportional to the enzyme concentration Signup and view all the answers

How does pH affect enzyme activity?

It can denature an enzyme or alter its ionic state Signup and view all the answers

What effect does temperature have on enzymatic reactions?

Temperature increases molecular movement, which enhances reactions until denaturation Signup and view all the answers

What does Vmax represent in enzymatic reactions?

The maximum rate of an enzymatic reaction under saturating substrate conditions Signup and view all the answers

Which of the following statements about enzyme concentration is accurate?

Higher enzyme concentrations lead to faster reactions if substrate is sufficient Signup and view all the answers

Which statement regarding optimal pH for enzymes is true?

Enzymes require varying pH ranges to function properly Signup and view all the answers

What is the relationship between temperature increases and reaction rate in enzymatic processes?

Reaction rates double with each 10-degree temperature increase until denaturation occurs Signup and view all the answers

Study Notes

Enzymes

Enzymes are specific biological proteins that catalyze biochemical reactions
They do not alter the reaction's equilibrium point and are not consumed or changed
Reactions are frequently specific and essential to many physiological functions
Enzymes appear in serum following cellular injury (or sometimes, in degraded cells)
Enzyme levels in serum are often used to diagnose diseases or physiological abnormalities

General Properties and Definitions

Enzymes catalyze specific physiological reactions.
Their structure includes primary (amino acid sequence), secondary (polypeptide chains), tertiary (structural cavities), and quaternary (relationship between subunits) structures.
Contain active sites, which are cavities where substrates interact with specific charged amino acids.
Allosteric sites are cavities other than the active site that may bind regulator molecules, impacting the basic enzyme structure
Enzymes can exist in different forms (isoenzymes) within the same individual, differing in properties like electrophoretic mobility, solubility, or resistance to inactivation.

Enzyme Classification and Nomenclature

The Enzyme Commission (EC) of the IUB developed a classification system.
Enzymes are assigned a systematic name that includes substrate, the reaction, and any coenzyme.
A shorter, recommended name is also given.
Each enzyme has a unique EC numerical code (four digits separated by decimals).
The first digit classifies the enzyme into one of six classes (oxidoreductases, transferases, hydrolases, lyases, isomerases, and ligases).

Enzyme Kinetics

Enzyme-catalyzed reactions proceed faster than uncatalyzed reactions due to lowering of activation energy.
The ES complex forms when a substrate binds to an enzyme's active site.
The Michaelis-Menten constant (Km) refers to substrate concentration at which the reaction velocity is half of its maximum.
The rate of reaction varies depending on substrate concentration (high substrate -> zero-order kinetics; low substrate -> first-order kinetics).
Reaction rate also depends on temperature, pH, and enzyme concentration.

Factors Affecting Enzymatic Reactions

Substrate Concentration: Higher substrate concentration results in higher reaction rates up to a maximum velocity point.
Enzyme Concentration: Higher enzyme concentration directly impacts the reaction rate, given adequate substrate concentration.
Temperature: Optimal temperature for reactions exists, enzyme denaturation occurring at very high temperatures.
pH: Enzyme activity depends on pH optima with denaturation happening significantly outside this range.

Inhibitors

Inhibitors are substances impacting enzyme activity.
Competitive Inhibitors: Bind to the active site, competing with the substrate, increasing Km, but not affecting Vmax.
Noncompetitive Inhibitors: Bind to a different site affecting both Km and Vmax.
Uncompetitive Inhibitors: Bind only to the ES complex, altering both Vmax and Km.
Mixed Inhibitors: Bind either the enzyme or the ES complex, affecting both Vmax and Km.

Enzyme Activity Measurement

Enzyme activity is measured by measuring the rate of product formation or substrate disappearance or the change in coenzyme concentration
There are fixed-time and continuous methods for enzyme measurement.
Standard units for reporting are activity units and the international unit (IU).

Enzymes in Clinical Significance

Various enzymes have different tissue origins and are measured to evaluate a range of conditions.
Elevated enzyme levels in serum can indicate certain conditions.
Specific isoenzyme analysis of enzymes aids in diagnosis.

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Description

This quiz explores the structure and function of enzymes, crucial biological proteins that catalyze biochemical reactions. Learn about their properties, active sites, and their role in physiological processes and disease diagnosis. Test your understanding of how enzymes operate and their importance in cellular functions.