Enzymes and Their Functions in Biology

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Questions and Answers

What is the role of enzymes in biochemical reactions?

To permanently alter the chemical structure of substrates.

To create new substrates for reactions.

To act as biochemical catalysts that speed up reactions. (correct)

To replace substrates in the reaction process.

Which part of an enzyme is responsible for binding the substrate?

Cofactor

Allosteric site

E-S Complex

Active site (correct)

What distinguishes cofactors from coenzymes?

Cofactors enhance enzyme activity only in the presence of other proteins.

Cofactors are always proteins, whereas coenzymes are not.

Cofactors can be inorganic or organic, while coenzymes are exclusively organic. (correct)

Cofactors bind permanently to enzymes, while coenzymes bind transiently.

What happens when a substrate binds to the active site of an enzyme?

It forms an E-S Complex. Signup and view all the answers

Which of the following is an example of a metal ion cofactor?

Iron (Fe) Signup and view all the answers

What is the energy required to start a chemical reaction called?

Activation Energy Signup and view all the answers

Which mechanism involves the formation of a covalent bond between the enzyme and substrates?

Covalent Catalysis Signup and view all the answers

Which type of catalysis relies on enzymes creating a region of high local substrate concentration?

Proximity Catalysis Signup and view all the answers

What effect does strain catalysis have on substrates?

It mimics transition state structures. Signup and view all the answers

Which is a characteristic of enzymes?

They exhibit high specificity and selectivity. Signup and view all the answers

How is activation energy typically lowered during enzymatic reactions?

By stabilizing the transition state. Signup and view all the answers

What is a chemical reaction?

An interaction that forms a new substance through chemical bonds Signup and view all the answers

What role do prosthetic groups play in acid-base catalysis?

They donate or remove protons. Signup and view all the answers

Which of the following is NOT considered evidence of a chemical change?

Change in shape Signup and view all the answers

What is the correct relationship between reactants and products in a chemical reaction?

Only atoms in reactants are present in products, and mass is conserved Signup and view all the answers

Which of the following is NOT a method to achieve a transition state during catalysis?

Increasing the activation energy Signup and view all the answers

Which statement reflects the importance of enzymes in biological reactions?

All biological reactions depend on enzymes to proceed quickly Signup and view all the answers

What does the law of conservation of mass state regarding chemical reactions?

Mass of reactants must equal the mass of products Signup and view all the answers

Which of the following best describes isozymes?

Different enzymes that catalyze the same reaction Signup and view all the answers

What happens during substrate binding in enzymes?

Substrates fit into enzymes, facilitating the reaction Signup and view all the answers

What would occur without enzyme catalysts in biological reactions?

Some reactions would take millions of years to occur Signup and view all the answers

What is the primary function of transferases in enzymatic reactions?

Transfer functional groups between compounds Signup and view all the answers

Which enzyme type is responsible for the hydrolytic cleavage of covalent bonds via water addition?

Hydrolases Signup and view all the answers

Which mechanism do lyases use to break chemical bonds?

Non-hydrolytic means Signup and view all the answers

What type of enzymes are isomerases primarily involved in transforming?

Isomeric forms of a molecule Signup and view all the answers

What distinguishes isozymes from regular enzymes?

Different amino acid sequences Signup and view all the answers

Which of the following is NOT an example of ligases?

Kinase Signup and view all the answers

What is the predominant form of lactate dehydrogenase (LDH) found in human serum?

LDH-2 Signup and view all the answers

Which type of enzyme would catalyze the transfer of a methyl group between molecules?

Transferase Signup and view all the answers

What is the primary role of the first attachment site in the Three-Point Attachment Model of enzymes?

Having the highest affinity and specificity Signup and view all the answers

Which of the following statements correctly characterizes the function of Trypsin?

It cleaves at sites containing lysine or arginine. Signup and view all the answers

Enzymes predominantly named for the reactions they catalyze, are categorized under which principle of enzyme naming?

Second principle Signup and view all the answers

Which category of enzymes is primarily responsible for oxidation-reduction reactions?

Oxidoreductases Signup and view all the answers

Which of the following enzyme names exemplifies the third principle of enzyme naming?

Glucose-6-Phosphate dehydrogenase Signup and view all the answers

What type of reaction do dehydrogenases specifically facilitate?

Transfer of hydrogen to NAD+/NADP+ Signup and view all the answers

What type of classification do ligases fall under in the enzyme classification system?

They are involved in the formation of new bonds via ATP hydrolysis. Signup and view all the answers

Which reaction would hydroxylases be involved in?

Addition of OH groups to substrates Signup and view all the answers

Study Notes

Enzymes in Biological Reactions

Enzymes are biochemical catalysts that accelerate chemical reactions without being changed in the process.
Essential for all biological reactions within human cells; without enzymes, reactions would be too slow to support life.
Dr. Richard Wolfenden emphasizes the time difference: reactions can take up to 1 trillion years without enzymes but are catalyzed in milliseconds.

Chemical Reactions

Involves a process where substances (reactants) interact to form new products with a change in chemical bonds.
Reactants must contact each other, leading to broken bonds and rearrangement to form products, adhering to the Law of Conservation of Mass.

Activation Energy

Minimum energy requirement for a chemical reaction to proceed, necessary despite the overall favorability of the process.
Enzymes lower activation energy, facilitating quicker reactions through mechanisms including proximity, strain, and stabilization of transition states.

Mechanisms of Enzyme Catalysis

Catalysis by Proximity: Enzymes arrange substrates for optimal interaction within the active site.
Catalysis by Strain: Enzymes bind substrates in a way that distorts their conformation, mimicking the transition state.
Covalent Catalysis: Formation of a transient covalent bond between enzyme and substrate.
Acid-Base Catalysis: Utilizes prosthetic groups of enzymes to donate or accept protons, facilitating reaction steps.

Enzyme Classification

Enzymes are classified into six main categories:
- Oxidoreductases: Catalyze oxidation-reduction reactions.
- Transferases: Transfer functional groups between molecules.
- Hydrolases: Catalyze hydrolytic cleavage involving water.
- Lyases: Break bonds without hydrolysis or oxidation, forming double bonds.
- Isomerases: Transfer functional groups within molecules to form isomers.
- Ligases: Join molecules together utilizing ATP hydrolysis.

Isozymes

Isozymes are enzyme variants that catalyze the same reaction but differ in structure and amino acid sequence.
Example: Lactate Dehydrogenase (LDH) has five isoforms in humans, each found in specific tissues (e.g., LDH-1 in the heart, LDH-5 in the liver).

Substrate Binding and Regulation

The active site of an enzyme binds the substrate, forming an Enzyme-Substrate (E-S) complex.
Enzymatic activity can be regulated through allosteric sites that serve as modulating sites, influencing the enzyme's function.

Naming Enzymes

Typically, enzymes have names ending in “-ase.” Naming also reflects the reaction type or substrate involved.
Example substrates or functions used in naming include dehydrogenases and lipases.

Characteristics of Enzymes

Enzymes are neither consumed nor permanently altered in reactions, making them reusable.
Exhibit high specificity for their substrates, with many having stereospecific preferences for enantiomers.

Clinical Relevance

Enzyme levels and isoform expression can indicate specific diseases, such as myocardial infarction and liver disease. Detection of LDH isoforms aids in diagnosing tissue-specific injuries.

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Description

This quiz focuses on the concept of enzymes, detailing their biological roles and the mechanisms by which they catalyze reactions in the human body. Explore different types of enzymes, their functions, and the importance of isozymes in a biomedical context.