Đề 2 – Bài tập, đề thi trắc nghiệm online Hóa sinh enzyme

Size exclusion chromatography (also known as gel filtration chromatography) separates molecules based on their size. The stationary phase consists of porous beads. Smaller molecules can enter the pores and thus have a longer path through the column, while larger molecules cannot enter the pores and elute earlier. This makes it effective for separating proteins of different sizes.

Competitive inhibitors resemble the substrate and bind reversibly to the active site, preventing substrate binding and thus reducing enzyme activity. This type of inhibition can be overcome by increasing substrate concentration.

pH changes can alter the ionization state of amino acid residues in the enzyme, particularly those in the active site or involved in maintaining the enzyme`s tertiary structure. This can affect substrate binding, catalysis, and overall enzyme stability, leading to changes in activity. Each enzyme has an optimal pH range for maximum activity.

Creatine kinase (CK), particularly the CK-MB isoenzyme, and troponin are cardiac markers released into the blood when heart muscle is damaged during a myocardial infarction. Measuring their levels helps diagnose heart attacks and assess the extent of cardiac damage.

Hexokinase catalyzes the transfer of a phosphate group from ATP to glucose, forming glucose-6-phosphate and ADP. This is the first committed step in glycolysis. Transferases are characterized by the transfer of functional groups; in this case, it`s a phosphate group.

Allosteric enzymes are regulated by molecules called effectors (activators or inhibitors) that bind at regulatory sites distinct from the active site. This binding induces conformational changes that alter the enzyme`s affinity for the substrate or its catalytic activity. Effectors can either enhance or reduce enzyme activity.

DNA ligase catalyzes the formation of a phosphodiester bond between the 3`-hydroxyl group and the 5`-phosphate group of adjacent DNA strands, effectively `ligating` or joining them together. This is a classic example of a ligase reaction, often requiring ATP as an energy source.

Isoenzymes allow for tissue-specific or developmentally regulated enzyme activity. Different isoenzymes may have different kinetic properties, regulatory mechanisms, or optimal conditions, enabling fine-tuning of metabolic pathways in various tissues or under different physiological conditions.

Phosphorylation, the addition of a phosphate group, is a reversible covalent modification that can either activate or inhibit enzyme activity. The effect depends on the specific enzyme and where phosphorylation occurs. For some enzymes, phosphorylation increases activity, while for others, it decreases activity.

Affinity chromatography relies on the specific and reversible binding of a protein to a ligand that is immobilized on a matrix. The target enzyme is selectively adsorbed to the ligand, while other proteins do not bind or bind weakly. The bound enzyme can then be eluted by changing conditions to disrupt the binding, resulting in high purification.

Lipases are hydrolases that catalyze the hydrolysis of ester bonds in lipids (fats), breaking down triglycerides into fatty acids and glycerol by adding water. Hydrolases use water to cleave chemical bonds.

Vmax (maximum velocity) represents the highest possible rate of an enzyme-catalyzed reaction when the enzyme is fully saturated with substrate. It reflects the enzyme`s catalytic capacity under optimal conditions.

Non-competitive inhibitors bind to an allosteric site, causing a conformational change in the enzyme that reduces its catalytic efficiency. This lowers Vmax because the maximum rate achievable is reduced, but Km remains unchanged as the inhibitor does not affect substrate binding to the active site.

Uncompetitive inhibitors bind to the enzyme-substrate complex, preventing the complex from forming product. This results in a decrease in both Vmax (because the maximum rate is lowered) and Km (because the inhibitor binding increases the apparent affinity of the enzyme for the substrate). Both Vmax and Km are decreased by the same factor, so the slope of the Lineweaver-Burk plot remains unchanged.

Proteases (also known as peptidases or proteinases) are enzymes that hydrolyze peptide bonds in proteins. They are used in laundry detergents to break down protein-based stains like blood, sweat, and food residues, making them easier to wash away.

Lactase is a beta-galactosidase, which is a type of hydrolase. It catalyzes the hydrolysis of the beta-glycosidic bond in lactose, breaking it down into glucose and galactose. Hydrolases use water to break chemical bonds.

The active site is the specific region of an enzyme where substrate molecules bind and undergo a chemical reaction, facilitated by the enzyme.

In ELISA, an enzyme is conjugated to an antibody or antigen. This enzyme catalyzes a reaction that produces a colored, fluorescent, or luminescent product, which is then measured to quantify the target molecule. The enzyme acts as a signal amplifier, making the assay highly sensitive.

Penicillin is a beta-lactam antibiotic that inhibits bacterial transpeptidase enzymes. These enzymes are essential for the synthesis of peptidoglycans, which are crucial components of bacterial cell walls. By inhibiting transpeptidases, penicillin prevents cell wall synthesis, leading to bacterial cell death.

Coenzymes are often considered as substrates in enzyme-catalyzed reactions, binding transiently and dissociating, whereas prosthetic groups are permanently associated with the enzyme, often through covalent bonds, and are essential for its activity.

DNA polymerase catalyzes the transfer of deoxyribonucleotide monophosphates from deoxyribonucleoside triphosphates to DNA, effectively transferring a phosphate group and adding nucleotides to a growing DNA strand. Transferases are enzymes that catalyze the transfer of functional groups (e.g., phosphate, methyl) between molecules.

Glucose-6-phosphate isomerase (also known as phosphoglucose isomerase) catalyzes the reversible isomerization of glucose-6-phosphate to fructose-6-phosphate, a key step in glycolysis and gluconeogenesis. Isomerases catalyze intramolecular rearrangements.

In feedback inhibition, the end-product of a metabolic pathway acts as an inhibitor, usually allosteric, of an enzyme earlier in the pathway. This mechanism helps to regulate the pathway`s output by slowing down or stopping production when sufficient product is available.

Generally, enzyme activity increases with temperature due to increased kinetic energy of molecules, leading to more frequent enzyme-substrate collisions. However, beyond an optimal temperature, the enzyme`s structure starts to denature, leading to a rapid decrease in activity.

Lyases catalyze cleavage of bonds (C-C, C-O, C-N, etc.) by elimination, leaving double bonds or rings, or conversely adding groups to double bonds. The decarboxylation of pyruvate is a typical lyase reaction involving the breaking of a C-C bond without hydrolysis or oxidation.

Km is the Michaelis-Menten constant, defined as the substrate concentration at which the reaction velocity is half of the maximum velocity (Vmax). It is an indicator of the affinity of an enzyme for its substrate; a lower Km indicates higher affinity.

Lactate dehydrogenase (LDH) catalyzes the reversible interconversion of lactate and pyruvate, involving the transfer of electrons (oxidation-reduction). Specifically, it catalyzes the oxidation of lactate to pyruvate, with the concomitant reduction of NAD+ to NADH. Oxidoreductases handle redox reactions.

Enzyme specificity arises from the unique 3D structure of the active site, which is complementary to the shape and chemical properties of specific substrates, allowing only those substrates to bind effectively and undergo catalysis.

Enzymes lower the activation energy required for a reaction to occur, thus speeding up the reaction rate without being consumed or altering the reaction`s equilibrium.

Synthesizing enzymes as zymogens (proenzymes) prevents them from being active in the cells where they are produced and allows for controlled activation at the correct time and place. This is particularly important for enzymes like digestive enzymes and blood clotting factors, where premature activity could be harmful.