Enzyme Kinetics and Km Value Quiz

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Questions and Answers

What does the Km value indicate about a substrate's affinity for an enzyme?

Km has no significance in enzyme kinetics.

A lower Km indicates a higher affinity. (correct)

A higher Km indicates a higher affinity.

A lower Km indicates a higher substrate concentration is needed.

Given Km1: 2 mM for enzyme 1 and Km2: 7 mM for enzyme 2, which enzyme exhibits a lower affinity for glucose?

Enzyme 1.

Both enzymes have the same affinity.

Affinity cannot be determined from the provided information.

Enzyme 2. (correct)

How can the Lineweaver-Burk plot be derived from the Michaelis-Menten equation?

By integrating the equation.

By taking the natural logarithm of both sides.

By transforming the equation into a double reciprocal format. (correct)

By differentiating the equation.

What is true about the relationship between Km and substrate concentration?

Higher Km values require higher substrate concentrations to reach Vmax. Signup and view all the answers

What would be the impact of increasing the Km value for an enzyme?

It would lower the enzyme's activity at low substrate concentrations. Signup and view all the answers

What is the role of cofactors in enzymatic reactions?

They are bound to enzymes for activity. Signup and view all the answers

What term is used for an inactive enzyme lacking its cofactor?

Apoenzyme Signup and view all the answers

Which class of enzymes is responsible for transferring groups within molecules?

Transferase Signup and view all the answers

Which enzyme classification is responsible for hydrolysis reactions?

Hydrolase Signup and view all the answers

What does the plateau phase in the Michaelis-Menten equation signify?

All enzyme’s active sites are fully occupied. Signup and view all the answers

Which of the following best describes Vmax in the context of enzyme kinetics?

The maximum velocity of the enzyme reaction. Signup and view all the answers

What is the function of coenzymes in enzymatic reactions?

They are organic components bound to enzymes. Signup and view all the answers

Which class of enzymes is involved in the formation of double bonds by removal of a group?

Lyase Signup and view all the answers

What is the primary function of a catalyst in a chemical reaction?

To speed up the reaction without being consumed Signup and view all the answers

Which of the following statements about enzymes is incorrect?

All enzymes require cofactors to function. Signup and view all the answers

What type of substance is trypsin and where is it activated?

A proenzyme activated in the small intestine Signup and view all the answers

Which statement correctly describes ribozymes?

They are RNA molecules capable of catalyzing specific biochemical reactions. Signup and view all the answers

What effect does high temperature generally have on enzymes made of proteins?

It denatures them by altering their 3D structure. Signup and view all the answers

Which enzyme works effectively in an acidic environment?

Pepsin Signup and view all the answers

Which of these is a property of enzymes related to their reactants?

They have highly specific substrates. Signup and view all the answers

Which factor does not affect enzyme activity?

Color of the enzyme Signup and view all the answers

What is the primary characteristic of competitive inhibition in enzymes?

It binds to an active site and competes with the substrate. Signup and view all the answers

In the context of enzyme kinetics, what does the y-intercept of a Lineweaver-Burk plot represent?

The inverse of Vmax. Signup and view all the answers

What type of enzyme inhibition is characterized by a slower dissociation of the inhibitor?

Irreversible inhibition. Signup and view all the answers

How does a non-competitive inhibitor affect Vmax and KM?

It decreases Vmax without affecting KM. Signup and view all the answers

Which of the following correctly describes the effect of a competitive inhibitor?

It can be overcome by increasing the concentration of substrate. Signup and view all the answers

What happens to the enzyme activity in non-competitive inhibition when substrate concentration increases?

Enzyme activity remains unchanged. Signup and view all the answers

In a Lineweaver-Burk plot, what does a steeper slope indicate?

Lower enzyme activity. Signup and view all the answers

Which type of inhibition does not allow Vmax to resume by increasing substrate concentration?

Non-competitive inhibition. Signup and view all the answers

What is the effect of un-competitive inhibition on Vmax?

It decreases Vmax. Signup and view all the answers

Which of the following types of inhibition targets the enzyme-substrate complex exclusively?

Un-competitive inhibition Signup and view all the answers

How does a non-competitive inhibitor affect an enzyme's activity?

It binds to both the free enzyme and the enzyme-substrate complex. Signup and view all the answers

Which factor increases the effectiveness of un-competitive inhibitors?

Increasing substrate concentration. Signup and view all the answers

What type of bond typically forms between an irreversible inhibitor and the enzyme?

Covalent bond Signup and view all the answers

Which of the following is an example of an irreversible inhibitor?

Aspirin Signup and view all the answers

What happens to the KM of an enzyme when un-competitive inhibition occurs?

KM decreases. Signup and view all the answers

Which statement is true regarding competitive inhibition?

It targets the free enzyme. Signup and view all the answers

What is the role of ser-529 in the context of enzyme inhibition?

It is the location where acetylation occurs by aspirin. Signup and view all the answers

What characterizes an irreversible enzyme inhibitor?

It forms a covalent bond with the enzyme. Signup and view all the answers

Which step is considered the rate-limiting step in a metabolic pathway?

The step with the highest activation energy. Signup and view all the answers

How does product inhibition affect enzymatic reactions?

It slows down the reaction rates when excess product is formed. Signup and view all the answers

What is a zymogen?

An inactive precursor of an enzyme. Signup and view all the answers

What happens when there is excessive product in a metabolic pathway?

It can lead to product inhibition. Signup and view all the answers

Why is ser-529 significant in relation to aspirin's mechanism of action?

It undergoes acetylation, leading to irreversible inhibition. Signup and view all the answers

What is the function of the rate-determining step in a metabolic pathway?

To act as the slowest step, limiting the rate of the pathway. Signup and view all the answers

Study Notes

Course Information

Course Title: Foundation Course For Health Sciences II
Course Code: MEDF 1012A
Instructor: Dr. Yeung Hang Mee, Po
Email: [email protected]
Office: Choh-Ming Li Basic Medical Sciences Building 6/F Room 610P

Learning Objectives

Describe the structures and components of enzymes
Understand enzyme kinetics, including the Michaelis-Menten equation and Lineweaver-Burk plot
Explain different types of enzyme inhibitions with examples
Review multiple factors affecting enzyme activity

Biocatalyst

A catalyst speeds up a chemical reaction, compared to the same reaction without a catalyst
A catalyst is not consumed in the reaction and can be recycled
A catalyst increases the rate of a reaction by lowering the activation energy

Structures and Components of Enzymes

Most enzymes are proteins
Enzymes require cofactors (inorganic) or coenzymes (organic)
Some enzymes are ribonucleic acids (RNA) called ribozymes
Ribozymes catalyze specific biochemical reactions
Ribozymes are found in the ribosome where they join amino acids to form protein chains

General Properties of Enzymes

Enzymes have highly specific reactants called substrates that bind to the active site
Trypsin is formed in the small intestine when its proenzyme form, trypsinogen, produced by the pancreas, is activated
Trypsin cleaves peptide chains mainly at the carboxyl side of the amino acids lysine or arginine
Enzymes operate effectively at specific pH and temperature ranges
Pepsin (stomach) works effectively at very acidic environments
Trypsin (activated at duodenum) works effectively at alkaline environments
Alkaline phosphatase (bones and liver) works effectively at alkaline environments
Most enzymes (made of proteins) are denatured at high temperatures due to changes in their 3D structure

Cofactors

Cofactors are inorganic components that are bound to enzymes for activity
An inactive enzyme without a cofactor is called an apoenzyme
Examples include inorganic metal ions such as zinc, copper, and ferric ions

Coenzymes

Coenzymes are organic components bound to enzymes for activity
An inactive enzyme without a coenzyme is also called an apoenzyme
Examples include flavin adenine nucleotide (FAD) and nicotinamide adenine dinucleotide (NADH)

Classifications of Enzymes

Each enzyme is assigned a four-digit classification number and a systematic name according to the reaction catalyzed
Specific examples listed include ATP-glucose phosphotransferase (EC 2.7.1.1) (hexokinase)

Classifications of Enzymes (continued)

Enzymes are classified based on the type of reaction they catalyze
Listed classes include Oxidoreductases, Transferases, Hydrolases, Lyases, Isomerases, and Ligases

Activation Energy in Catalyzed Reactions

Enzymes can provide alternative pathways with lower activation energy for chemical reactions

Enzyme Kinetics

The Michaelis-Menten equation reflects the change in velocity of enzymatic reactions under different substrate concentrations

Michaelis-Menten Equation

Vmax is the maximum velocity an enzyme can reach
Km is a specific value of substrate concentration where the velocity of enzymatic reaction reaches half Vmax
Km value indicates substrate affinity for the enzyme

Transformation of Michaelis-Menten Equation into Lineweaver-Burk Plot

The Lineweaver-Burk plot is a linear transformation of the Michaelis-Menten equation
The plot allows for easy determination of Km and Vmax values

Enzyme Inhibitions

A reversible inhibition occurs when the inhibitor rapidly dissociates from the enzyme or enzyme-substrate complex
Types include competitive, non-competitive, and un-competitive inhibition
An irreversible inhibition occurs when the inhibitor very slowly dissociates from the enzyme or enzyme-substrate complex

Reversibly Competitive Inhibition

A competitive inhibitor binds to the active site of an enzyme, competing with the substrate
This results in an apparent increase in Km, but Vmax remains unchanged

Reversibly Non-Competitive Inhibition

A non-competitive inhibitor binds to a site other than the active site, decreasing Vmax
KM is not significantly affected

Reversibly Un-competitive Inhibition

An un-competitive inhibitor binds to the enzyme-substrate complex, which lowers both Vmax and Km

Types of Enzyme Inhibition by Lineweaver-Burk Plot

The Lineweaver-Burk plot provides a visual representation of how different types of inhibition affect enzymatic activity

Irreversibly Inhibition

This type of enzyme inhibitor binds strongly to the active site, forming a covalent bond with the enzyme.
An example, Aspirin, works by binding to the active site of cyclooxygenase (COX)

Factors Affecting Enzyme's Activity

Various factors affect enzyme activity, such as substrate concentration, pH, temperature, and inhibitors

Rate-determining Step

The slowest step in a metabolic pathway is the rate-limiting step

Product Inhibition

The product of an enzymatic reaction can inhibit the overall reaction rate

Zymogen

Zymogen is an inactive precursor of an enzyme; also called a pro-enzyme
Conversion of active enzyme from its zymogen involves specific proteolytic cleavage
Examples include pepsinogen and trypsinogen

Premature Activation of Zymogen

Premature activation can occur in acute pancreatitis, leading to tissue damage

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Description

This quiz explores key concepts in enzyme kinetics, focusing on the Km value and its implications for substrate affinity. Test your understanding of how to interpret Km values, differentiate enzyme affinities, derive the Lineweaver-Burk plot, and understand the relationship between Km and substrate concentration. Perfect for students studying biochemistry and enzymology.