BIOCHEMISTRY in Questions and Answers - Alimov A.M. - 2016

SECTION 3. ENZYMES

Question 1. What are Enzymes?

Answer: Enzymes are biological catalysts that accelerate biochemical reactions.

Question 2. What is the Chemical Nature of biological catalysts?

Answer: Enzymes are a highly specialized Class of protein-based substances.

Question 3. What properties are unique to enzymes?

Answer. 1. High catalytic activity

2. Specificity

3. Regulatability

Question 4. What are the stages of an enzymatic reaction?

Answer: The following stages are distinguished:

- binding of the substrate molecule to the enzyme;

- Conversion of the primary intermediate into one or more successive (transition) complexes;

- dissociation of the end products from the enzyme.

For example, Е+S ⇄ ES+P (Е - enzyme, S - substrate, Р - product)

Question 5. What is meant by "activation energy"?

Answer: Activation energy is the energy required to bring molecules into an activated state; the higher the activation energy, the slower the reaction proceeds.

Question 6. How do enzymes affect activation energy?

Answer. Enzymes lower the activation energy, thereby increasing the reaction rate at a relatively low Temperature.

Question 7. What determines the Specificity of Enzyme Action?

Answer: The complementarity between the Active Site of the enzyme and the substrate.

Question 8. What types of substrate specificity do enzymes exhibit?

Answer: 1. Absolute specificity (enzymes catalyze The conversion of only a single substrate)

2. Group specificity (enzymes act on specific chemical groups or types of bonds)

3. Stereospecificity (the enzyme catalyzes the conversion of only specific spatial isomers of a single substance)

Question 9. What factors affect enzymatic activity?

Answer: 1. Substrate Concentration

2. Enzyme amount

3. Medium pH

4. Temperature

5. Presence of activators and inhibitors

6. Presence of Coenzymes

Question 10. What is the Michaelis constant (Km)?

Answer: Km is defined as the substrate concentration at which the enzymatic reaction rate is half of the maximum. Km reflects the affinity of the enzyme for the substrate

Question 11. In what units is Km expressed?

Answer. Km is expressed in units of substrate concentration

Question 12. What is the active site of an enzyme?

Answer. The active site is a unique combination of several amino acid residues involved in the binding and conversion of the substrate. It includes the catalytic and substrate-binding sites. The substrate-binding site (the "anchoring pad") is responsible for substrate attachment, while the catalytic site is directly involved in substrate transformation

Question 13. Which model of enzyme-substrate interaction was proposed by Fischer?

Answer: According to Fischer's model, the substrate fits the active site of the enzyme "like a lock and key"

Question 14. What is the induced-fit model?

Answer: In Koshland's induced-fit model, the substrate induces Conformational Changes in the enzyme, resulting in the realignment of amino acid residues involved in substrate binding ("hand in glove")

Question 15. What is meant by enzyme activity?

Answer: The rate of the catalyzed reaction

Question 16. What are inhibitors?

Answer: Inhibitors are substances that decrease enzymatic activity

Question 17. What forms of Enzyme Inhibition exist and what do they mean?

Answer: A distinction is made between reversible and irreversible inhibition. Irreversible inhibition occurs when an inhibitor binds permanently to the enzyme. Reversible inhibition can be competitive and noncompetitive

Question 15. What are Competitive Inhibitors?

Answer: Competitive inhibitors are substances with a Structure similar to the substrate, thus competing with it for binding to the active site of the enzyme

Question 19. What are some Examples of competitive inhibitors?

Answer 1. Malonate (^-COOH-CH₂-COO^-) for succinate dehydrogenase

2. Inorganic phosphate (P_i) for Phosphatases

3. proteinase inhibitor (protein) for Trypsin and similar proteinases

Question 20. How do kinetic constants change during competitive inhibition?

Answer: Km increases, V_max remains unchanged

Question 21. What are noncompetitive inhibitors?

Answer: The inhibitor is structurally dissimilar to the substrate and does not compete with it for the binding site in the active center, but instead blocks the groups of the catalytic region of the active center. As a result, V_max decreases, while Km remains unchanged

Question 22. What are activators?

Answer: Activators are substances that enhance enzymatic activity

Question 23. What is The Role of metals in Enzymatic Catalysis?

Answer: Metals are involved in:

1. Stabilization of a specific enzyme conformation

2. Formation of the true substrate

3. Binding of the coenzyme

4. Formation of the active site

Question 24. How is the Rate of Enzymatic processes regulated?

Answer: 1. By The amount of the enzyme present, through changes in its synthesis or degradation rate

2. By the amount of substrates

3. By altering the catalytic activity of enzymes

Question 25. What are constitutive enzymes?

Answer. Enzymes whose level remains constant throughout The Cell's life and is independent of The addition of Inducers

Question 26. What are inducible enzymes?

Answer: Enzymes that are synthesized only in response to the presence of specific low-molecular-weight inducers

Question 27. What are proenzymes?

Answer: Proenzymes are inactive precursor Proteins that are converted into active enzymes through selective Cleavage (Limited proteolysis)

Question 28. What is enzyme compartmentalization?

Answer: This is the spatial Separation of metabolic processes within the cell (e.g., fatty acid synthesis enzymes are located in the Cytoplasm, while degradation enzymes, i.e., those involved in fatty acid β-oxidation, reside in the mitochondrial matrix)

Question 29. What is feedback regulation?

Answer: This is the Regulation of the rate of a biochemical process by its end product

Question 30. How is the rate of biochemical processes regulated via feedback mechanisms?

Answer: 1. The end product of the reaction suppresses the expression of genes encoding the key enzyme for the synthesis of this substance

2. The end product allosterically inhibits the enzyme that catalyzes one of the initial reactions in the pathway

Question 31. What is an allosteric site?

Answer: A region on the enzyme molecule, distinct from the active site, to which a low-molecular-weight compound binds. This induces A change in the Tertiary Structure of the protein and, consequently, in its enzymatic activity

Question 32. How is enzyme activity regulated through phosphorylation-dephosphorylation?

Answer: 1. Phosphorylation involves The transfer of a phosphate group from ATP to the OH group of an amino acid residue in the enzyme protein, mediated by protein kinase

2. Dephosphorylation involves the hydrolytic removal of the phosphate group from the protein by protein phosphatases

Question 33. What is The basis of Enzyme Classification?

Answer: All Enzymes are classified According to the type of chemical reaction they catalyze

Question 34. What classes of enzymes exist?

Answer: I - Oxidoreductases. These enzymes catalyze redox reactions (Lactate dehydrogenase - LDH)

II - Transferases. They catalyze the intermolecular transfer of groups (aspartate aminotransferase - AST, Alanine aminotransferase - ALT)

III - Hydrolases. They catalyze the cleavage of molecules with the participation of Water (amylase and other digestive enzymes)

IV - Lyases. Enzymes that remove groups from substrates via non-hydrolytic pathways (fumarase, aldolase)

V - Isomerases. They catalyze the interconversion of isomers (Triosephosphate isomerase)

VI - Ligases. They catalyze the joining of two molecules coupled with the expenditure of energy from ATP or other high-energy compounds (acetyl-CoA carboxylase)

Question 35. What are isozymes?

Answer: These are Multiple Forms of an enzyme that catalyze the same reaction. They are encoded by different genes, and therefore differ somewhat in their Primary Structure and, consequently, in their physicochemical and catalytic properties.

Question 36. What is the composition and localization of LDH coenzymes? Answer:

Question 37. How are enzymes used in medicine and veterinary science?

Answer: Enzymes are used in the Treatment (enzymotherapy) and Diagnosis of diseases (enzymodiagnostics), as well as in enzyme immunoassay

Question 38. What are the Applications of enzymes (enzyme preparations) in animal husbandry?

Answer: They are used to improve the digestibility and assimilation of feed nutrients that are difficult for the body to access

Question 39. What does "Enzyme Immobilization" mean?

Answer: Enzyme immobilization is the conversion of enzymes into an insoluble state while preserving (partially or fully) their catalytic activity. Both Physical and Chemical Methods OF IMMOBILIZATION are employed