Đề 14 – Bài tập, đề thi trắc nghiệm online Hóa sinh enzyme

Enzymes are versatile biocatalysts used in numerous industrial sectors. Key applications include food processing (e.g., cheese making, brewing), detergent industry (proteases and lipases for stain removal), and pharmaceutical industry (drug synthesis, diagnostics, and therapeutics).

Factors like substrate and enzyme concentrations, temperature, pH, and inhibitors directly influence enzyme activity. The color of the reaction solution, unless it directly interferes with the enzyme or substrate (which is highly unlikely in typical biochemical contexts), is generally irrelevant to enzyme kinetics.

Competitive inhibitors primarily affect the Km of an enzyme. By competing for the active site, they increase the apparent Km (more substrate is needed to reach half Vmax), but at sufficiently high substrate concentrations, the Vmax can still be reached. Non-competitive inhibitors, in contrast, mainly reduce Vmax without significantly altering Km.

Non-competitive inhibitors bind to an enzyme at a site distinct from the active site (allosteric site). This binding causes a conformational change in the enzyme, which distorts the active site and reduces or eliminates its catalytic activity, regardless of substrate concentration.

Km reflects the affinity of an enzyme for its substrate. A higher Km value means that a higher substrate concentration is needed to reach half of Vmax, indicating a weaker binding interaction and thus a lower affinity of the enzyme for the substrate.

Competitive inhibitors resemble the substrate and compete for binding to the enzyme`s active site. By occupying the active site, they prevent the actual substrate from binding and being catalyzed, thus inhibiting enzyme activity.

Enzyme specificity arises from the unique 3D structure of its active site. This site is shaped to perfectly fit a specific substrate, much like a lock and key, allowing for precise interaction and catalysis.

Oxidoreductases are enzymes that catalyze redox (oxidation-reduction) reactions. These reactions involve the transfer of electrons from one molecule (the reductant) to another (the oxidant). Examples include dehydrogenases and oxidases.

Enzymes are biological catalysts, meaning they accelerate chemical reactions without being consumed in the process. Their primary role is to speed up biochemical reactions essential for life.

Enzyme specificity is primarily attributed to the unique and precise 3D structure of their active sites. This structure is complementary to the shape, charge, and chemical properties of specific substrates, allowing enzymes to bind and catalyze reactions on only those substrates with high fidelity.

In competitive inhibition, increasing substrate concentration can overcome the effect of the inhibitor. At sufficiently high substrate levels, the substrate will outcompete the inhibitor for binding to the active site, and the reaction rate can eventually reach Vmax, although a higher substrate concentration is needed compared to the uninhibited reaction.

Allosteric enzymes are regulated by molecules binding at sites distinct from the active site, known as allosteric sites. This binding can induce conformational changes that either increase or decrease the enzyme`s activity. This is a key mechanism for metabolic regulation.

The induced-fit model is a refinement of the lock-and-key model. It proposes that the active site of the enzyme is not a rigid pre-formed shape but rather is flexible. Upon substrate binding, the enzyme undergoes a conformational change to more precisely fit the substrate and facilitate catalysis. This dynamic interaction is more accurate than the rigid lock-and-key concept.

Cofactors are non-protein chemical entities that are essential for the activity of some enzymes. They can be inorganic ions or organic molecules (coenzymes) and participate in the catalytic reaction, often by carrying electrons or functional groups.

Enzymes are classified into six main classes based on the type of reaction they catalyze. Lyases are one of these classes, known for catalyzing the breaking of chemical bonds by means other than hydrolysis or oxidation, often forming new double bonds or rings. Trypsin, catalase, and amylase are specific enzyme names, not classes of enzymes based on reaction type.

Enzyme deficiencies, often due to genetic mutations, can disrupt metabolic pathways. If an enzyme is deficient or non-functional, a specific metabolic step is blocked, leading to the accumulation of substrates or deficiency of products, resulting in various metabolic disorders (e.g., phenylketonuria, Tay-Sachs disease).

Enzymes are catalysts and, by definition, are not consumed in the reactions they catalyze. They participate in the reaction mechanism but are regenerated in their original form at the end, allowing them to catalyze multiple reaction cycles. Options 1, 2, and 4 are all true characteristics of enzymes.

Feedback inhibition is a crucial regulatory mechanism in metabolic pathways. Typically, the end product of a pathway acts as an allosteric inhibitor of an enzyme early in the same pathway. This prevents overproduction of the end product and maintains metabolic balance by `feeding back` to reduce pathway activity when product levels are sufficient.

An apoenzyme is the protein part of an enzyme that is inactive on its own because it lacks an essential cofactor. A holoenzyme is the complete, catalytically active enzyme, which includes both the apoenzyme and its required cofactor (either a coenzyme or a metal ion).

Non-competitive inhibitors reduce enzyme activity by altering the enzyme`s conformation, regardless of substrate concentration. Increasing substrate concentration cannot overcome non-competitive inhibition. The Vmax of the reaction is reduced, and the reaction will plateau at a lower maximum rate compared to the uninhibited enzyme.

Denaturation disrupts the enzyme`s three-dimensional structure, including the active site. Since the active site`s specific shape is crucial for substrate binding and catalysis, denaturation leads to a loss or significant reduction in the enzyme`s ability to function as a catalyst.

Vmax (maximum velocity) in enzyme kinetics represents the highest possible rate of an enzyme-catalyzed reaction at saturating substrate concentrations. It indicates the enzyme`s maximal catalytic capacity under given conditions.

Coenzymes are organic cofactors. They are often derived from vitamins and are crucial for the function of many enzymes, typically acting as carriers of electrons, atoms, or functional groups in metabolic reactions.

The lock-and-key model, an earlier concept of enzyme-substrate interaction, proposes that the enzyme`s active site and the substrate have rigid, complementary shapes that fit perfectly together, similar to a lock and its key. While simplified, it highlights the importance of shape complementarity.

Km, or the Michaelis constant, is a measure of the substrate concentration required to achieve half of the maximum reaction rate (Vmax). It is an indicator of the enzyme`s affinity for its substrate; a lower Km generally indicates a higher affinity.

Hydrolases are a class of enzymes that catalyze hydrolysis reactions. These reactions involve breaking chemical bonds with the addition of water. Examples include enzymes that digest proteins, carbohydrates, and lipids.

Enzymes are crucial in medical diagnostics. Their specificity and catalytic activity are exploited to detect and quantify specific substances (like glucose, cholesterol, or specific enzymes themselves as disease markers) in body fluids such as blood and urine, aiding in disease diagnosis and monitoring.

Each enzyme has an optimal pH at which it functions most effectively. This pH is determined by the enzyme`s specific environment and the ionization states of amino acid residues in the active site that are crucial for substrate binding and catalysis. Deviations from the optimal pH can reduce enzyme activity or lead to denaturation.

Enzymes do not change the overall free energy change or the equilibrium of a reaction. Instead, they accelerate reactions by providing an alternative reaction pathway that requires less activation energy. This is often achieved through mechanisms like transition state stabilization and providing a favorable microenvironment.

Proteases are enzymes that break down proteins. In laundry detergents, they are used to effectively remove protein-based stains like blood, sweat, and food residues from fabrics by hydrolyzing the peptide bonds in these stains, making them easier to wash away.