Enzymes and Their Activity Units

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Questions and Answers

What is the primary role of Coenzyme A (CoASH)?

Carrying the acyl group of fatty acids (correct)

Functioning as a coenzyme for vitamin C

Serving as a reducing agent in oxidative phosphorylation

Acting as a hydrogen donor in insulin regulation

Which vitamin acts as a coenzyme for the enzymes dopamine oxidase and polyphenol oxidase?

Vitamin B2 (Riboflavin)

Vitamin B1 (Thiamin)

Vitamin C (L-ascorbic acid) (correct)

Vitamin B3 (Niacin)

Which compound is described as a hydrogen carrier in oxidative decarboxylation?

Biotin

Pyridoxal phosphate

Coenzyme Q (Ubiquinone)

Lipoic acid (correct)

What function does Pyridoxal phosphate primarily serve?

Coenzyme for transamination and decarboxylation Signup and view all the answers

Which amino acid is part of the tripeptide known as Glutathion?

Cysteine Signup and view all the answers

What is the primary role of enzymes in biological systems?

To increase the rate of chemical reactions Signup and view all the answers

Which of the following describes a holoenzyme?

An enzyme made up of both a protein part and a non-protein part Signup and view all the answers

What is a common characteristic of ribozymes?

They can catalyze the cleavage of nucleic acids Signup and view all the answers

How is enzyme activity expressed in terms of International Units (IU)?

Amount of enzyme that converts one micromole of substrate per minute Signup and view all the answers

What distinguishes a coenzyme from a prosthetic group?

Prosthetic groups are usually derivatives of vitamins Signup and view all the answers

Where are intracellular enzymes primarily produced?

In the cytosol or endoplasmic reticulum Signup and view all the answers

Which of the following best describes coenzymes?

They can accept or donate groups during reactions Signup and view all the answers

Which of the following enzymes is classified as an extracellular enzyme?

Pepsin Signup and view all the answers

Which enzyme acts specifically on α (1,4) glycosidic bonds?

Amylase Signup and view all the answers

What term describes enzymes that are produced in an inactive form?

Zymogens Signup and view all the answers

Which of the following methods can activate zymogens?

By HCl Signup and view all the answers

The enzyme L-amino acid oxidase is specific for which type of substrate?

L-amino acids Signup and view all the answers

What type of enzymes catalyze the transfer of phosphate groups?

Kinases Signup and view all the answers

Which enzyme catalyzes both oxidation and decarboxylation reactions of citrate?

Isocitrate dehydrogenase Signup and view all the answers

What is the primary role of oxidases in biochemical reactions?

Removing hydrogen from a substrate Signup and view all the answers

Which enzyme class is responsible for hydrolyzing glycosidic bonds?

Carbohydrases Signup and view all the answers

Which of the following enzymes is categorized as a peroxidase?

Catalase Signup and view all the answers

Which of the following statements is true for dehydrogenases?

Many depend on NAD⁺ and FAD. Signup and view all the answers

Which statement correctly describes optical specificity?

Enzymes only act on one specific optical isomer. Signup and view all the answers

What function do lyases perform in biochemical reactions?

Remove groups from substances to form double bonds Signup and view all the answers

Which of the following enzymes is an example of a dioxygenase?

Tryptophan pyrrolase Signup and view all the answers

Which enzyme class includes enzymes that catalyze the interconversion of isomers?

Isomerases Signup and view all the answers

Which enzyme would hydrolyze the ester bond of triglycerides?

Lipase Signup and view all the answers

What type of reaction do oxidases participate in?

Oxidation involving oxygen Signup and view all the answers

Which of the following substances is a non-specific irreversible inhibitor of enzymes?

Heat Signup and view all the answers

What effect does fluoride ion (F⁻) have on enzyme activity?

Inhibits by precipitating calcium ions Signup and view all the answers

Which substance is known to react with the thiol (SH) group of enzymes leading to irreversible inhibition?

Iodoacetic acid Signup and view all the answers

What is the role of antithrombin III in enzyme inhibition?

It irreversibly inhibits thrombin Signup and view all the answers

Which of the following can bind to Fe ions and inhibit cytochrome oxidase enzyme activity?

Carbon monoxide Signup and view all the answers

Which of the following substances is secreted to protect the stomach lining against pepsin?

Mucin Signup and view all the answers

What type of agents are organo-phosphorus compounds like Malathion classified as?

Irreversible inhibitors Signup and view all the answers

What is the primary reason why certain irreversible inhibitors cannot be reversed?

They change the enzyme structure permanently Signup and view all the answers

What is the role of inducers in enzyme synthesis?

They enhance the rate of enzyme synthesis. Signup and view all the answers

Which type of effector binds non-covalently at the allosteric site to stimulate catalytic reactions?

Positive effectors Signup and view all the answers

How does feedback inhibition affect enzyme activity?

It inhibits the activity of the first enzyme in the pathway. Signup and view all the answers

What happens to the kinetic curve in allosteric regulation compared to Michaelis-Menten kinetics?

It becomes sigmoidal. Signup and view all the answers

What effect does glucagon have on glycolytic enzyme synthesis?

It decreases the synthesis of key glycolytic enzymes. Signup and view all the answers

What is the mechanism of reversible covalent modification in enzyme regulation?

Addition or removal of phosphate groups. Signup and view all the answers

Which of the following accurately describes feedback regulation?

It targets the gene for the first enzyme's synthesis. Signup and view all the answers

Which of the following statements is true about allosteric enzymes?

They have a regulatory site separate from the active site. Signup and view all the answers

Study Notes

Enzymes

Enzymes are protein catalysts, increasing the rate of biochemical reactions without being changed themselves.
All enzymes are proteins, except some RNA molecules (ribozymes) which act as enzymes, typically catalyzing phosphodiester bond cleavage and synthesis.
A substrate is the substance upon which an enzyme acts.
Enzymes are categorized into intracellular and extracellular types.
- Intracellular enzymes work inside cells (e.g., metabolic enzymes).
- Extracellular enzymes are produced inside but act outside cells (e.g., digestive enzymes).
- Enzymes are primarily synthesized in the cytosol or ER, and some in the mitochondria.
- They are present in all body cells and fluids (plasma, CSF), and intracellular compartments.

Enzyme Activity Units

International Unit (IU): Indicates the amount of enzyme catalyzing the conversion of one micromole of substrate to product per minute (1 IU = 1 µmol/min).
Katal: Represents the amount of enzyme catalyzing the conversion of one mole of substrate to product per second (1 Katal = 1 mol/s).

Enzyme Nature

Mostly protein-based.
Can exist as simple enzymes (only protein) or holoenzymes (protein plus non-protein cofactor).
- Cofactors can be organic (vitamins) or inorganic (metal ions like Fe²⁺, Zn²⁺, Mg²⁺).

Prosthetic groups and Co-enzymes

Prosthetic group: A small organic molecule covalently bonded to the apoenzyme (protein portion).
Coenzyme: A small organic molecule non-covalently bonded to the apoenzyme. Often derived from vitamins and can accept or donate specific groups during a reaction.

Enzyme Specificity

Absolute: One enzyme catalyzes only one substrate.
Group: An enzyme catalyzes reactions involving specific functional groups.
Stereo: One enzyme catalyzes reactions utilizing only one stereoisomer of a substrate.
Dual: An enzyme catalyzes reactions on two substrates simultaneously.

Enzyme Classification

Enzyme Commission (EC) numbers categorize enzymes based on the type of reaction they catalyze (e.g., oxidation-reduction, transfer).
Each EC number has four parts identifying the reaction type, functional groups, coenzymes and substrate.

Enzyme Active Sites

The active site of an enzyme is a specific region that binds the substrate.
Complementary active site shape and functional groups allow binding of reactants to catalyze a reaction.
Enzyme-substrate complex temporarily forms during catalysis within the active site where reactions occur and products are formed.

Catalytic Efficiency

Enzymes dramatically increase reaction rates compared to non-enzymatic reactions (e.g., 10⁸ to 10¹⁰ times faster.)
Usually, each enzyme molecule can convert 10⁰ to 10³ substrate molecules into product per second.

Enzyme Kinetics

Kinetics studies the rates of enzyme-catalyzed reactions.
Velocity (rate) is the increase in product or decrease in substrate concentration over time.
Initial velocity (V₀) is measured at the beginning of the reaction when substrate concentration is high and product is low.
The Michaelis-Menten equation describes the relationship between initial velocity (V₀), maximum velocity (Vₘₐₓ), and substrate concentration ([S]). This relates to enzyme affinity by substrate concentration [Km]. Km is a constant where V₀ is half Vₘₐₓ.

Enzyme Inhibition

Inhibitors reduce enzyme activity.
- Competitive inhibition: Inhibitors compete with the substrate for the active site, reducing substrate binding.
- Non-competitive inhibition: Inhibitors bind to a different site, altering the enzyme's conformation and preventing the substrate from binding effectively, or affecting catalysis.
- Uncompetitive inhibition: Inhibitors bind specifically to a complex formed from enzyme and substrate thus slowing the reaction or preventing products from detaching from the active site.)

Enzyme Regulation

Enzyme activity can be regulated by various factors:
- Concentration of an enzyme (synthesis and adaptation rates).
- Allosteric regulation, whereby an effector (molecule) binds to a site other than the active site, altering enzyme conformation, leading to an increase or decrease in enzyme activity.
  - Positive allosteric effectors: Increase enzyme activity.
  - Negative allosteric effectors: Decrease enzyme activity.
- Feedback inhibition: End products of a biosynthetic pathway inhibit an earlier enzyme in the pathway.
- Covalent modification (phosphorylation/dephosphorylation): Enzymes can be activated or deactivated by adding or removing phosphate groups.

Plasma Enzymes

Plasma enzymes are categorized into functional and non-functional:
- Functional plasma enzymes are present in high concentrations and have roles in blood.
- Non-functional plasma enzymes are present in minor quantities and do not have roles in blood, but can be indicative of cellular damage. Examples include AST, ALT, ALP, and CPK.

Isoenzymes

Isoenzymes are different forms of the same enzyme, differing in structure but having the same catalytic function.
Isoenzymes exhibit varying levels across body tissues and are used in diagnostics of diseases (e.g., heart attack, liver disease).

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Description

This quiz explores the fascinating world of enzymes, including their roles as protein catalysts and their categorization into intracellular and extracellular types. Additionally, it covers enzyme activity units such as International Unit (IU) and Katal. Test your knowledge on enzyme functions and their significance in biochemical reactions.