Enzymes Overview

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Questions and Answers

What class of enzyme is represented by the enzyme commission number 2.7.1.1?

Oxidoreductases

Hydrolases

Ligases

Transferases (correct)

Which type of specificity is illustrated by chymotrypsin, which hydrolyzes peptide bonds near aromatic amino acids?

Group specificity (correct)

Linkage specificity

Absolute specificity

Stereochemical specificity

What is the primary role of an enzyme in a chemical reaction?

To consume energy during the reaction

To increase the rate of the reaction (correct)

To change the substrates into products

To alter the equilibrium of the reaction

Which factor does NOT affect enzymatic activity?

Color of substrates Signup and view all the answers

In the reaction coordinate diagram, the activation energy is characterized by which of the following?

The energy required to reach the transition state Signup and view all the answers

What is the role of enzymes in chemical reactions?

They increase reaction rates without being consumed. Signup and view all the answers

Which of the following statements about enzymes is incorrect?

Enzymes affect the equilibrium of the reactions. Signup and view all the answers

What term describes a complete active enzyme with its bound cofactor or coenzyme?

Holoenzyme Signup and view all the answers

Which of the following best describes cofactors?

They can be inorganic ions or complex organic molecules. Signup and view all the answers

Which class of enzymes catalyzes the transfer of functional groups from one substance to another?

Transferases Signup and view all the answers

What distinguishes a prosthetic group from a cofactor or coenzyme?

It is tightly or covalently bound to an enzyme. Signup and view all the answers

How do enzymes contribute to biological processes compared to non-biological catalysts?

Enzymes are more efficient and work under mild conditions. Signup and view all the answers

What characteristic of enzymes is primarily related to their specificity?

Their molecular structure and shape. Signup and view all the answers

Which enzyme class is responsible for hydrolysis reactions?

Hydrolases Signup and view all the answers

What type of reaction do ligases catalyze?

Joining molecules using energy from ATP Signup and view all the answers

Which of the following enzymes would be classified as an isomerase?

Triose phosphate isomerase Signup and view all the answers

Which of the following is an example of a transferase?

Choline acyltransferase Signup and view all the answers

What distinguishes lyases from other enzyme classes?

They cleave C-C, C-N, C-O or C-S bonds without hydrolysis Signup and view all the answers

Which reaction best illustrates the action of oxidoreductases?

Lactate + NAD+ + H+ → Pyruvate + NADH Signup and view all the answers

Identify the primary function of hydrolases in the digestive system.

To break down complex molecules by hydrolysis Signup and view all the answers

Which enzyme example is classified as a ligase?

Glutamine synthetase Signup and view all the answers

Which statement correctly describes the effect of enzymes on reaction rates?

Enzymes lower the activation energy required for a reaction. Signup and view all the answers

What is the role of activators in enzyme activity?

Activators increase the activity of enzymes. Signup and view all the answers

How do enzymes generally bind to substrates according to the induced fit model?

The enzyme binds better to the transition state than to the substrate. Signup and view all the answers

Which enzyme listed has the highest rate enhancement?

Orotidine monophosphate decarboxylase Signup and view all the answers

What type of enzyme inhibitor permanently binds to an enzyme?

Irreversible inhibitor Signup and view all the answers

What effect does a higher activation energy have on a reaction rate?

It slows down the reaction. Signup and view all the answers

Which statement is true regarding the 'lock and key' model of enzyme action?

It can be misleading and oversimplifies enzyme interactions. Signup and view all the answers

What happens to an enzyme's activity if its metal ion activators are removed?

The enzyme becomes inactive or less active. Signup and view all the answers

What is the effect of competitive inhibitors on the Vmax and Km of an enzyme?

No change in Vmax; apparent increase in Km Signup and view all the answers

Which type of inhibition only binds to the enzyme-substrate complex?

Uncompetitive inhibition Signup and view all the answers

What characterizes allosteric enzymes?

They undergo conformational changes upon binding of modulators Signup and view all the answers

Which of the following statements is true about mixed inhibition?

It affects both substrate binding and catalysis Signup and view all the answers

Which enzyme isoenzyme is primarily associated with myocardial infarction?

Lactate dehydrogenase (LDH) Signup and view all the answers

What happens to the levels of creatine phosphokinase (CPK) following a muscle injury?

Levels increase within hours and remain high for days Signup and view all the answers

What distinguishes isoenzymes from regular enzymes?

They catalyze the same reaction but vary in efficiency Signup and view all the answers

In which manner do allosteric modulators affect enzyme activity?

They bind noncovalently and may enhance or inhibit activity Signup and view all the answers

What is the primary role of regulatory enzymes in metabolic pathways?

They often act as switches responding to cellular signals Signup and view all the answers

Study Notes

Enzymes

Enzymes are biological catalysts that speed up reactions
Enzymes are effective in small amounts, very efficient
Enzymes do not affect the reaction equilibrium, but increase reaction rates.
Most, but not all, enzymes are globular proteins.
Enzymes work under mild conditions of temperature and pH.
Some enzymes require cofactors
Coenzymes are complex organic or metalloorganic molecules bound to an enzyme
Apoprotein is the protein part of a holoenzyme, and the Holoenzyme is the complete active enzyme with its coenzyme and cofactors
Enzymes are classified into six classes, each with subclasses:
- Oxidoreductases catalyze oxidation-reduction reactions
- Transferases transfer functional groups between molecules
- Hydrolases break down molecules by hydrolysis
- Lyases break down molecules, but not by hydrolysis
- Isomerases rearrange atoms within a molecule
- Ligases join two molecules together
Enzymes show specificity:
- Absolute specificity means an enzyme acts only on one substrate
- Stereochemical specificity means an enzyme acts only on one stereoisomer
- Linkage specificity means an enzyme acts on a specific bond, regardless of neighboring groups
- Group specificity means an enzyme acts on a specific linkage and also requires neighboring groups
Factors affecting enzymatic activity include:
- Enzyme concentration, substrate concentration, temperature, and pH.
The active site of an enzyme binds to the substrate
The mechanism of enzymatic catalysis involves an enzyme-substrate complex, then an enzyme-product complex, followed by the release of the product
Enzymes lower the activation energy of a reaction
Enzymes are more complimentary to the transition state of a reaction than to the substrate itself
Enzyme activation can occur through the binding of activators, often metal ions
Enzyme inhibitors decrease enzymatic activity
Irreversible inhibitors bind covalently to the enzyme, inactivating it permanently
Reversible inhibitors bind noncovalently to the enzyme and can dissociate
Types of reversible inhibitors include:
- Competitive inhibition
  - The inhibitor competes with the substrate for binding to the active site, increasing the apparent Km, but not changing Vmax.
- Uncompetitive inhibition
  - The inhibitor binds to the enzyme-substrate complex, decreasing both Vmax and Km.
- Mixed inhibition
  - The inhibitor binds to the enzyme with or without substrate, decreasing Vmax and changing Km.
Regulatory enzymes are often the first enzyme in a metabolic pathway, controlling the overall rate of the pathway
Allosteric enzymes are regulated by reversible, noncovalent binding of allosteric modulators to regulatory sites
Damaged cells release enzymes into the bloodstream, which can be used to diagnose disease
Isoenzymes catalyze the same reaction but with different efficiencies, and are often found in different tissues or organelles
LDH isozymes are found in different tissues and their levels are often elevated in these tissues
- LDH1 increases in myocardial infarction
- CPK3 increases in muscle injury.
- ALP isozymes are found in different tissues, and their levels are often elevated in these tissues.

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Description

This quiz covers key concepts related to enzymes, including their function as biological catalysts, classification into six main classes, and the roles of cofactors and coenzymes. Test your knowledge on how enzymes speed up reactions and their specificity in various biochemical processes.