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Enzymes are exclusively protein-based catalysts, with no other biological molecules capable of accelerating chemical reactions in living systems.
Answer: False
While most enzymes are proteins, catalytic RNA molecules (ribozymes) and biomolecular condensates are also recognized as biological catalysts capable of accelerating reactions in living systems.
Enzymes are characterized by their high specificity and sensitivity to environmental factors such as temperature and pH, and they are regenerated at the end of each catalytic cycle.
Answer: True
Enzymes exhibit high specificity and are sensitive to environmental conditions like temperature and pH. A key characteristic of catalysts, including enzymes, is that they are regenerated unchanged at the conclusion of the reaction.
Exposure to extreme temperatures or pH levels can cause an enzyme to denature, leading to a loss of its specific three-dimensional structure and catalytic function.
Answer: True
Extreme conditions, such as non-optimal temperatures or pH, can cause an enzyme to denature, resulting in the loss of its unique three-dimensional structure and, consequently, its catalytic activity.
Isozymes are different enzymes that catalyze the same chemical reaction but may have different amino acid sequences or structures.
Answer: True
Isozymes are indeed distinct enzymes that catalyze the same reaction but can differ in their amino acid sequences or overall structures.
The active site of an enzyme is a large region comprising most of the enzyme's overall structure, directly involved in both binding and catalysis.
Answer: False
The active site is a specific, typically small region of an enzyme, often involving only 2-4 amino acids, that is directly involved in catalysis and substrate binding, not most of the enzyme's overall structure.
Enzymes like kinases and phosphatases are involved in signal transduction and cell regulation, while ATPases contribute to movement and transport within cells.
Answer: True
Kinases and phosphatases are indeed crucial for signal transduction and cell regulation, and ATPases are involved in cellular movement and transport, as described in the diverse functions of enzymes.
What is the fundamental definition of an enzyme and its primary role in biological systems?
Answer: An enzyme is a protein that functions as a biological catalyst, accelerating chemical reactions without being consumed.
What happens to an enzyme's function if it is exposed to conditions outside its optimal range, such as extreme pH?
Answer: It undergoes denaturation, losing its specific three-dimensional structure and catalytic function.
What is the 'active site' of an enzyme primarily composed of?
Answer: A specific region with a catalytic site and one or more binding sites.
Anselme Payen, a French chemist, was the first to discover an enzyme in 1833, which he named 'zymase'.
Answer: False
Anselme Payen discovered the first enzyme in 1833, naming it 'diastase'. Eduard Buchner later discovered 'zymase' in 1897.
Louis Pasteur initially believed that fermentation was a 'vital force' that could only occur within living yeast cells, a theory later disproven by Eduard Buchner.
Answer: True
Louis Pasteur's 'vital force' theory, which posited that fermentation required living cells, was indeed disproven by Eduard Buchner's demonstration of cell-free fermentation.
The term 'enzyme' was coined by Wilhelm Kühne in 1877, deriving from a Greek word meaning 'leavened' or 'in yeast'.
Answer: True
Wilhelm Kühne coined the term 'enzyme' in 1877, drawing from the Greek 'énzymon,' which means 'leavened' or 'in yeast,' reflecting its historical association with fermentation.
James B. Sumner, John Howard Northrop, and Wendell Meredith Stanley jointly received the Nobel Prize for proving that enzymes are pure carbohydrates.
Answer: False
James B. Sumner, John Howard Northrop, and Wendell Meredith Stanley received the Nobel Prize for definitively proving that enzymes are pure proteins, not carbohydrates.
The atomic-level structure of enzymes was first determined for lysozyme in 1965 using X-ray crystallography, initiating the field of structural biology.
Answer: True
The first atomic-level structure of an enzyme, lysozyme, was indeed determined in 1965 using X-ray crystallography, a milestone that launched the field of structural biology.
Enzymes are classified by the International Union of Biochemistry and Molecular Biology (IUBMB) primarily based on their amino acid sequence similarity.
Answer: False
The IUBMB classifies enzymes primarily based on their reaction mechanism using EC numbers, not primarily on amino acid sequence similarity, although sequence similarity is another criterion for classification.
The EC number system's first digit broadly classifies enzymes based on their evolutionary relationship.
Answer: False
The EC number system's first digit classifies enzymes based on their reaction mechanism, not their evolutionary relationship. EC categories do not necessarily reflect sequence similarity.
Which historical observation preceded the formal discovery of enzymes?
Answer: The digestion of meat by stomach secretions.
Who was the first person to discover an enzyme and what did they name it?
Answer: Anselme Payen, who named it 'diastase'.
What was Louis Pasteur's initial conclusion regarding fermentation?
Answer: Fermentation was a 'vital force' that could only occur within living yeast cells.
Eduard Buchner received the Nobel Prize in Chemistry for which discovery?
Answer: Discovering cell-free fermentation.
Following Buchner's example, how are enzymes typically named?
Answer: By adding the suffix '-ase' to the name of their substrate or the reaction type.
Who definitively proved that enzymes are pure proteins?
Answer: James B. Sumner, John Howard Northrop, and Wendell Meredith Stanley.
What method was first used to determine the atomic-level structure of enzymes?
Answer: X-ray crystallography
What are the two primary criteria used to classify enzymes?
Answer: Their amino acid sequence similarity or their enzymatic activity.
According to the EC number system, which class of enzymes catalyzes oxidation/reduction reactions?
Answer: EC 1, Oxidoreductases
The primary role of an enzyme is to significantly increase the activation energy of a chemical reaction, thereby speeding up the process.
Answer: False
Enzymes accelerate chemical reactions by significantly lowering the activation energy, not increasing it.
The 'lock and key' model, proposed by Daniel Koshland, suggests that enzymes are flexible structures that reshape upon substrate binding.
Answer: False
The 'lock and key' model was proposed by Emil Fischer and describes rigid enzyme-substrate fitting. The 'induced fit' model, proposed by Daniel Koshland, describes flexible enzyme structures that reshape upon substrate binding.
Enzymes accelerate reactions by increasing the entropy change and forming higher-energy covalent intermediates with the substrate.
Answer: False
Enzymes accelerate reactions by reducing unfavorable entropy changes and forming lower-energy covalent intermediates, not higher-energy ones.
Enzyme dynamics refers to the internal motions of an enzyme's structure, which can involve movements of individual amino acid residues or entire protein domains, and are linked to functional aspects.
Answer: True
Enzyme dynamics indeed describes the complex internal motions within an enzyme's structure, from individual residues to entire domains, and these motions are intrinsically linked to the enzyme's functional characteristics.
Cofactors are always inorganic molecules, such as metal ions, that enzymes require for full activity.
Answer: False
Cofactors can be inorganic molecules like metal ions, but they can also be organic compounds, such as flavin and heme.
Coenzymes are organic cofactors that are tightly, often covalently, bound to an enzyme and remain associated with it throughout the catalytic cycle.
Answer: False
Coenzymes are organic cofactors that are typically released from the enzyme and transport chemical groups. Prosthetic groups are the organic cofactors that are tightly, often covalently, bound.
A holoenzyme is an inactive enzyme that requires a cofactor but does not currently have one bound.
Answer: False
A holoenzyme is the active, complete form of an enzyme with its cofactor(s) bound. An apoenzyme is the inactive form lacking its cofactor.
Many coenzymes are derived from vitamins, which are essential organic compounds that the body can synthesize de novo.
Answer: False
Many coenzymes are derived from vitamins, but vitamins are essential organic compounds that the body cannot synthesize de novo and must obtain from the diet.
Enzyme kinetics, which studies how enzymes bind to substrates and convert them into products, was quantitatively theorized by Leonor Michaelis and Maud Leonora Menten.
Answer: True
Leonor Michaelis and Maud Leonora Menten indeed developed the foundational quantitative theory of enzyme kinetics, describing how enzymes interact with substrates and catalyze their conversion to products.
Vmax represents the substrate concentration required for an enzyme to reach half of its maximum reaction rate.
Answer: False
Vmax represents the maximum reaction rate when the enzyme is saturated with substrate. Km (Michaelis-Menten constant) represents the substrate concentration required for an enzyme to reach half of its Vmax.
Catalytically perfect enzymes are those whose specificity constant is limited only by the rate at which the substrate diffuses to the enzyme.
Answer: True
Catalytically perfect enzymes are characterized by a specificity constant that approaches the diffusion limit, meaning their reaction rate is solely limited by the rate of substrate diffusion to the active site.
How do enzymes primarily influence the rate of chemical reactions?
Answer: By lowering the reaction's activation energy.
Which model of enzyme-substrate binding suggests that enzymes are flexible structures that reshape upon interaction with the substrate?
Answer: The 'induced fit' model.
How do enzymes accelerate reactions at a molecular level?
Answer: By distorting bound substrates into their transition state form and orienting them productively.
What is 'substrate presentation' in the context of enzyme mechanism?
Answer: The spatial separation of an enzyme from its substrate, or its sequestration near the substrate to initiate activity.
What is the difference between coenzymes and prosthetic groups?
Answer: Coenzymes are released and transport groups, while prosthetic groups are tightly bound and remain associated.
What is an apoenzyme?
Answer: An enzyme that requires a cofactor but does not currently have one bound, rendering it inactive.
Many coenzymes are derived from which essential organic compounds?
Answer: Vitamins
What does Km (Michaelis-Menten constant) represent in enzyme kinetics?
Answer: The substrate concentration required for an enzyme to reach half of its Vmax.
What is a 'catalytically perfect' enzyme?
Answer: An enzyme whose activity is limited only by the rate of substrate diffusion to it.
Allosteric modulation involves molecules binding directly to the active site, causing a conformational change that either increases or decreases the enzyme's reaction rate.
Answer: False
Allosteric modulation involves molecules binding to allosteric sites, which are distinct from the active site, to induce conformational changes that alter enzyme activity.
A competitive inhibitor binds to an enzyme at a site distinct from the active site, reducing catalytic efficiency without affecting substrate affinity.
Answer: False
A competitive inhibitor binds directly to the active site. A non-competitive inhibitor binds to a site distinct from the active site.
Irreversible enzyme inhibitors permanently inactivate an enzyme, often by forming a strong covalent bond, and their effects cannot be reversed by increasing substrate concentration.
Answer: True
Irreversible inhibitors form strong, often covalent, bonds with the enzyme, leading to permanent inactivation that cannot be overcome by increasing substrate concentration.
Enzyme inhibitors often function in organisms as part of a positive feedback mechanism, increasing the production of a metabolic pathway's end product.
Answer: False
Enzyme inhibitors typically function as part of a negative feedback mechanism, where the end product inhibits an initial enzyme in the pathway, thereby decreasing production.
Pepsin, an enzyme active in the stomach, functions optimally at a neutral pH of 7.0.
Answer: False
Pepsin functions optimally in highly acidic conditions, with an optimal pH range of 1.5–1.6, not a neutral pH of 7.0.
Enzyme activity in a cell is primarily controlled by only two mechanisms: regulation by activators/inhibitors and post-translational modification.
Answer: False
Enzyme activity is controlled by five main mechanisms: regulation by activators/inhibitors, post-translational modification, control of enzyme quantity, subcellular distribution, and organ specialization.
Post-translational modifications like phosphorylation and polypeptide chain cleavage can alter enzyme activity, as seen with zymogens.
Answer: True
Post-translational modifications, including phosphorylation and proteolytic cleavage (as in zymogen activation), are well-established mechanisms for altering enzyme activity.
The quantity of an enzyme is solely regulated by enzyme induction, which increases its production, without any mechanisms for decreasing its levels.
Answer: False
The quantity of an enzyme is regulated not only by induction (increasing production) but also by repression (diminishing production) and by altering the rate of enzyme degradation.
Organ specialization in multicellular eukaryotes involves cells in different organs expressing distinct sets of isozymes to suit their specialized metabolic needs.
Answer: True
Organ specialization involves the expression of distinct isozymes in different tissues, allowing cells to meet their unique metabolic demands.
How can the effect of a competitive inhibitor be overcome?
Answer: By increasing the substrate concentration.
Which type of inhibitor binds to an enzyme at a site distinct from the active site, reducing Vmax without affecting Km?
Answer: Non-competitive inhibitor
What defines an irreversible enzyme inhibitor?
Answer: It permanently inactivates an enzyme, typically by forming a strong covalent bond.
How do enzyme inhibitors function as part of feedback mechanisms in organisms?
Answer: They act as negative feedback, where the end product inhibits an initial enzyme in the pathway.
What is the optimal pH for pepsin, an enzyme active in the stomach?
Answer: 1.5–1.6
Which of the following is NOT one of the five main ways enzyme activity is controlled in a cell?
Answer: Alteration of enzyme's genetic code during activity
How does negative feedback regulate enzyme activity in metabolic pathways?
Answer: The end product of a pathway inhibits one of the initial enzymes.
Defects in DNA repair enzymes can lead to cancer due to the accumulation of mutations in the genome.
Answer: True
Defects in DNA repair enzymes impair a cell's ability to correct genetic errors, leading to an accumulation of mutations that can drive cancer development.
Enzymes evolve primarily through gene duplication followed by the complete redesign of the duplicate copies for entirely new functions.
Answer: False
While gene duplication is a mechanism for enzyme evolution, it often involves small changes in substrate binding specificity or acquisition of novel activities, not necessarily a complete redesign for entirely new functions. Evolution can also occur without duplication.
Artificial evolution is used in vitro to modify enzyme activity or specificity for industrial applications, sometimes even designing enzymes from scratch.
Answer: True
Artificial evolution is a key technique for engineering enzymes with desired properties for industrial use, including modifying existing activities or designing novel enzymes.
What is the consequence of defects in DNA repair enzymes?
Answer: Accumulation of mutations in the genome, potentially leading to cancer.
How do enzymes evolve over time?
Answer: Through mutations and sequence divergence, often involving gene duplication.
In the biofuel industry, ligninases are used to break down cellulose into fermentable sugars for ethanol production.
Answer: False
In the biofuel industry, cellulases are used to break down cellulose into fermentable sugars. Ligninases are used for the pretreatment of biomass.
Proteases, amylases, and lipases are commonly found in biological detergents to target protein, starch, and fat/oil stains, respectively.
Answer: True
Biological detergents indeed utilize proteases for protein, amylases for starch, and lipases for fat/oil stains, leveraging their specific catalytic actions.
In the brewing industry, amyloglucosidase and pullulanases are used to increase the protein content of beer.
Answer: False
Amyloglucosidase and pullulanases are used in brewing to create low-calorie beer and adjust fermentability by breaking down polysaccharides, not to increase protein content.
Papain, a proteolytic enzyme, is used in meat tenderizers to hydrolyze proteins, improving texture and digestibility.
Answer: True
Papain is a well-known proteolytic enzyme used in meat tenderizers to hydrolyze proteins, which enhances the meat's texture and makes it more digestible.
Which enzymes are used in the biofuel industry to break down cellulose into fermentable sugars?
Answer: Cellulases
What is a culinary application of enzymes mentioned in the text?
Answer: Using papain as a meat tenderizer.
What is the role of rennin (chymosin) in the dairy industry?
Answer: To hydrolyze protein during cheese manufacturing.
Which enzymes are essential tools in molecular biology for techniques like PCR and restriction digestion?
Answer: Nucleases, DNA ligase, and polymerases
What is an application of proteases in personal care?
Answer: To remove proteins that accumulate on contact lenses.
What is the application of amylases in the starch industry?
Answer: To convert starch into glucose and various syrups.