Enzymes and Their Functions

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Questions and Answers

What happens to enzyme activity as temperature increases up to its optimum temperature?

Enzyme activity becomes irreversible

Enzyme activity increases (correct)

Enzyme activity decreases

Enzyme activity remains constant

What is the effect of extreme pH changes on enzyme activity?

Enzyme becomes denatured (correct)

Enzyme activity improves

Enzyme activity doubles

Enzyme activity remains unaffected

Which of the following statements best describes competitive inhibition?

It lowers the reaction's activation energy

It increases the velocity of the reaction

It permanently alters enzyme structure

It competes with the substrate for the active site (correct)

At what temperature does enzyme activity virtually stop for most enzymes?

70 °C Signup and view all the answers

What is the effect of a competitive inhibitor on Vmax?

It has no effect on V<del>max</del> Signup and view all the answers

What is typically the optimum pH range for most enzymes?

5 to 9 Signup and view all the answers

What is a common outcome of enzyme activity deviating significantly from its optimum pH?

Marked changes in activity Signup and view all the answers

What type of enzyme inhibition occurs when an inhibitor binds to a site other than the active site?

Allosteric inhibition Signup and view all the answers

What do the amino acids at the active site primarily determine in enzyme catalysis?

The specificity of substrate binding Signup and view all the answers

What is the impact of an increased substrate concentration on enzyme activity?

It increases the reaction velocity until the enzyme is saturated. Signup and view all the answers

What is the primary function of enzymes in biochemical reactions?

To regulate the rate of biochemical reactions Signup and view all the answers

What defines the Michaelis constant (K_m)?

The substrate concentration at half-maximal velocity. Signup and view all the answers

Which of the following factors does NOT need to be varied when studying enzyme catalysis?

Product concentration Signup and view all the answers

Which characteristic is true for all enzymes?

They are not chemically altered by reactions Signup and view all the answers

How does the Michaelis-Menten equation assist in enzyme kinetics?

It illustrates the behavior of many enzymes with changing substrate concentration. Signup and view all the answers

What distinguishes a holoenzyme from an apoenzyme?

A holoenzyme contains a cofactor, while an apoenzyme does not Signup and view all the answers

Which condition could lead to a lower K_m value?

Higher enzyme affinity for substrate Signup and view all the answers

How does enzyme specificity relate to their function?

Enzymes interact only with specific substrates or related substrates Signup and view all the answers

What type of plot is used to simplify the analysis of enzyme kinetics?

Lineweaver-Burk plot Signup and view all the answers

Which suffix is commonly used in the nomenclature of enzymes?

-ase Signup and view all the answers

Which statement about the role of temperature in enzyme activity is true?

Each enzyme has an optimal temperature range for maximum activity. Signup and view all the answers

What roles do cofactors play in enzyme activity?

They are necessary for the activity of certain enzymes Signup and view all the answers

What is the significance of the 'induced fit model' in enzyme action?

It illustrates how enzymes change their shape to facilitate reactions Signup and view all the answers

What role do digestive enzymes play due to their low specificity?

They allow for the digestion of multiple food types efficiently Signup and view all the answers

What effect does a competitive inhibitor have on the apparent Km for a substrate?

It increases the apparent K<del>m</del>. Signup and view all the answers

Which drug acts as a competitive inhibitor of xanthine oxidase?

Allopurinol Signup and view all the answers

What is the primary mechanism by which sulfonamides inhibit bacterial growth?

They block folic acid synthesis from PABA. Signup and view all the answers

What is the effect of allosteric inhibitors on enzyme activity?

They decrease V<del>max</del> and may increase K<del>m</del>. Signup and view all the answers

Which statement about feedback inhibition is correct?

It regulates enzyme activity by the end products of the pathway. Signup and view all the answers

What role does warfarin play in the treatment of blood clotting disorders?

It is a structural analog of vitamin K. Signup and view all the answers

How do statins affect cholesterol levels in the body?

They inhibit the enzyme HMG-CoA reductase. Signup and view all the answers

In the context of enzyme activity, what happens at the regulatory site when an allosteric inhibitor binds?

It produces conformational changes that decrease activity. Signup and view all the answers

What is required for enzyme activation from its inactive form?

Proteolysis Signup and view all the answers

How does an allosteric activator affect an enzyme's affinity for its substrate?

Increases Vmax value Signup and view all the answers

Which statement is true about the isozymes of lactate dehydrogenase (LDH)?

They consist of different subunit combinations. Signup and view all the answers

What type of modification typically activates many enzymes?

Phosphorylation Signup and view all the answers

Which isozyme of lactate dehydrogenase is primarily associated with myocardial infarction?

Isozyme 1 (H4) Signup and view all the answers

What is the effect of dephosphorylation on enzyme activity?

Inactivates the enzyme Signup and view all the answers

What is autotocatalytic activation in relation to zymogens?

Self-activation of zymogen Signup and view all the answers

What role does AMP play in cellular metabolism?

It is an allosteric activator for certain enzymes. Signup and view all the answers

Which isozyme of creatine kinase is primarily found in brain tissues?

CK-BB Signup and view all the answers

In which type of tissue is CK-MB predominantly found?

Heart Signup and view all the answers

Which creatine kinase isozyme is associated with elevated plasma levels in muscle diseases?

CK-MM Signup and view all the answers

Which enzyme is primarily associated with prostate cancer diagnosis?

Acid phosphatase Signup and view all the answers

Alanine aminotransferase (ALT) is primarily derived from which organ?

Liver Signup and view all the answers

What is the primary source of alkaline phosphatase?

Liver and bone Signup and view all the answers

Which enzyme increases in plasma levels during pancreatitis?

Amylase Signup and view all the answers

What is the clinical application of aspartate aminotransferase (AST)?

Hepatic parenchymal disease marker Signup and view all the answers

Which enzyme is a marker for myocardial infarction?

Creatine kinase Signup and view all the answers

Which source provides lactate dehydrogenase?

Erythrocytes and heart Signup and view all the answers

Study Notes

Enzymes

Enzymes are biocatalysts, proteins that regulate the rate of biochemical reactions.
Produced by living cells, and sometimes function outside cells.
Needed in small quantities.
Accelerate reactions without changing themselves.
Highly specific, acting on a specific substrate or related substrates.

Enzyme Nomenclature

Most enzyme names end in "-ase" and are based on the substrate or the reaction's description.
Some retain trivial names (e.g., trypsin, pepsin).

Enzyme Specificity

Enzymes interact with specific substrates, catalyzing unique chemical reactions.
Specificity arises from the arrangement of chemical groups at the active site.
Enzymes usually only interact with one or a few related substrates.
Digestive enzymes have less specificity; intracellular enzymes are highly specific.

Chemical Nature

Mostly proteins (except for ribozymes).
Holoenzymes are active, containing non-protein components (cofactors).
Apoenzymes are inactive without cofactors.
Cofactors include organic molecules (coenzymes) or inorganic metal ions.

Mechanism of Enzyme Action (Induced Fit Model)

Enzymes contain an active site.
Active site binds the substrate, forming an enzyme-substrate complex.
This complex is transformed into an enzyme-product complex.
The enzyme is released with no change, and the substrate becomes a product.
Induced fit model describes substrate binding inducing a shape change in the enzyme.

Factors Affecting Enzyme Activity

Substrate concentration: Velocity increases with substrate concentration until saturation.
Enzyme concentration: Increased enzyme leads to increased reaction rate.
Inhibitors: Substances decreasing enzyme activity.
Cofactors: Essential for enzyme function (inorganic or organic molecules.)
Temperature: Optimum temperature exists for each enzyme, decreased activity outside this range.
pH: Optimum pH exists for each enzyme. Activity decreases outside this range.

Effect of Substrate Concentration

Michaelis-Menten equation describes enzyme behavior as substrate concentration changes.
Km (Michaelis constant): Substrate concentration at which the reaction rate is half of maximum.
Lower Km means higher enzyme affinity for its substrate.
Lineweaver-Burk plot (double-reciprocal plot): graph showing the relationship between reaction velocity and substrate concentration, transformed to a linear plot for calculating important kinetic parameters.

Effect of Temperature

Increased temperature increases activity initially due to increased kinetic energy and collisions.
Activity plateaus and then decreases rapidly above the optimum temperature due to enzyme denaturation.
Optimum temperature varies between enzymes (37°C for many animal enzymes; 50°C for many plant enzymes).

Effect of pH

Each enzyme has an optimal pH range.
Activity decreases outside this range, often due to altered charges on the enzyme or substrate, leading to denaturation.
Extreme changes in pH can cause irreversible inhibition.

Inhibition of Enzyme Activity

Reversible inhibition can be competitive or noncompetitive.
Irreversible inhibition denatures the enzyme, permanently damaging it.

Competitive Inhibitors

Structurally similar to the substrate.
Compete for the active site.
Increasing substrate concentration can overcome the inhibition.
Increase Km (decreased affinity.)
No effect on Vmax (maximum velocity)

Allosteric Inhibitors

Bind to the allosteric site, changing the enzyme's shape.
Binding can lead to inhibition or activation.
Varying substrate concentration has little effect on the inhibition or activation.
Do not bind to the active site directly.

Irreversible Inhibitors

Strong acids, alkalis, alcohols, or heavy metal salts.
Denature protein structure.
Examples include certain pesticides or poisons.

Isoenzymes

Different forms of an enzyme catalyzing the same reaction.
Differ in amino acid sequence, polypeptide structure, or regulatory properties.
Produced by different genes.

Control of Enzyme Synthesis

Inducers stimulate gene expression of enzymes.
Repressors inhibit gene expression of enzymes.

Control of Enzyme Degradation

Rate of enzyme synthesis determines the amount of enzyme.
Rate of enzyme degradation removes enzymes from the system.

Changing the Catalytic Activity of Enzymes

Activation of zymogens: Inactive precursors activated by removing part of their polypeptide chain (e.g., proteolysis).
Allosteric effectors: Molecules bind at allosteric sites, altering enzyme activity.
Covalent modification (phosphorylation/dephosphorylation): Enzymatic processes alter enzyme activity and sometimes cause the enzyme to lose its activity.

Isozymes- Lactate Dehydrogenase (LDH)

Tetrameric enzyme with H and M subunits in various combinations (H4 to M4).
Various isozymes have tissue-specific and clinical significance. (e.g. 1-L-DH is associated with heart function).

Isozymes- Creatine Kinase (CK)

Dimer enzyme with M and B subunits in combination. (CK-BB, CK-MB, CK-MM)
Varying isoenzyme levels in blood have diagnostic implications, as some forms are associated with specific tissues (e.g., heart damage).

Clinically Important Enzymes

Specified enzymes have particular clinical significance in various conditions (e.g., LDH, CPK.)
Particular diseases and clinical applications use enzymes as diagnostics. (e.g., Liver, heart, kidney problems.)

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Description

This quiz explores the fascinating world of enzymes, including their nature, specificity, and nomenclature. Understand how these biocatalysts play a critical role in biochemical reactions and why they are essential for life. Test your knowledge on enzyme classification and their chemical characteristics.