What is the basic mechanism by which enzymes catalyze biochemical reactions?
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Mastering this deck enables clinicians and students to understand how enzyme activity is regulated, predict effects of enzyme deficiencies, and interpret diagnostic enzyme tests, thereby improving diagnosis and management of metabolic disorders.
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|---|---|---|---|
| 1 | What is the basic mechanism by which enzymes catalyze biochemical reactions? |
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Focuses on enzyme mechanisms, factors affecting activity, regulation, and clinical relevance of enzyme dysfunction.
Enzymes lower the activation energy of reactions, thereby increasing the reaction rate without being consumed in the process. |
| Think of enzymes as biochemical catalysts that make reactions easier. |
| 2 | Define Vmax in enzyme kinetics. | Vmax is the maximum rate of an enzyme-catalyzed reaction when all active sites are saturated with substrate. | Vmax occurs at substrate saturation. |
| 3 | What is the Michaelis constant (Km)? | Km is the substrate concentration at which the reaction velocity is half of Vmax, reflecting enzyme affinity for substrate. | Lower Km indicates higher affinity. |
| 4 | How does increasing substrate concentration affect reaction rate below and above Km? | Below Km, reaction rate increases proportionally with substrate concentration; above Km, rate approaches Vmax and plateaus. | Think of a fill-level that rises quickly then levels off. |
| 5 | Explain the significance of enzyme cooperativity and the Hill coefficient. | Cooperativity occurs when substrate binding to one active site affects others; the Hill coefficient quantifies this effect, with >1 indicating positive cooperativity. | Think of hemoglobin as a cooperative protein. |
| 6 | What type of enzyme inhibition is characterized by a reversible decrease in Vmax and Km? | Mixed inhibition; it affects both Vmax and Km, depending on the inhibitor’s affinity for enzyme and enzyme-substrate complex. | Different from pure competitive or non-competitive inhibition. |
| 7 | Describe competitive inhibition and how it can be overcome. | Competitive inhibitors bind the active site, competing with substrate; increasing substrate concentration can outcompete the inhibitor. | Think of a race where more runners can outpace the blocker. |
| 8 | Describe non-competitive inhibition and its effect on Vmax and Km. | Non-competitive inhibitors bind allosteric sites, decreasing Vmax without changing Km. | Inhibition affects enzyme activity regardless of substrate levels. |
| 9 | What are allosteric enzymes and how do they regulate metabolism? | Allosteric enzymes have multiple binding sites and undergo conformational changes upon effector binding, allowing regulation of enzyme activity in response to cellular signals. | Think of a switch that turns activity up or down. |
| 10 | Name a key allosteric enzyme in glycolysis and its regulator. | Phosphofructokinase-1 (PFK-1); regulated by ATP (feedback inhibition) and AMP (activation). | A rate-limiting step in glycolysis. |
| 11 | How does covalent modification regulate enzyme activity? | Covalent modifications, such as phosphorylation, can activate or inhibit enzymes by changing their conformation or charge state. | Think of enzymes as switches modulated by phosphorylation. |
| 12 | What is the role of allosteric effectors in enzyme regulation? | Allosteric effectors bind to sites other than the active site to increase or decrease enzyme activity, enabling rapid regulation of metabolic pathways. | Effectors act as on/off switches. |
| 13 | Give an example of enzyme regulation via feedback inhibition. | ATP inhibits phosphofructokinase-1 in glycolysis when energy is sufficient, preventing unnecessary glucose breakdown. | A metabolic pathway that self-regulates to conserve resources. |
| 14 | What is enzyme induction and repression? | Enzyme induction increases enzyme synthesis in response to substrate presence; repression decreases synthesis when substrate is scarce. | Adaptive gene regulation. |
| 15 | How does the presence of a competitive inhibitor affect the apparent Km and Vmax? | Increases the apparent Km (decreases affinity), while Vmax remains unchanged. | Inhibitor competes with substrate for active site. |
| 16 | What clinical enzyme assay principle is used to detect tissue damage? | Measurement of enzyme activity in serum; elevated levels indicate cell damage releasing enzymes into circulation. | Think of enzymes as biomarkers for tissue injury. |
| 17 | Name an enzyme whose elevated serum levels are diagnostic for liver injury. | Alanine aminotransferase (ALT) and aspartate aminotransferase (AST). | Markers for hepatocellular damage. |
| 18 | Which enzyme deficiency causes phenylketonuria, and what is its role? | Phenylalanine hydroxylase; converts phenylalanine to tyrosine. | Deficiency leads to phenylalanine accumulation. |
| 19 | What is the effect of enzyme deficiency on metabolic pathways? | Enzyme deficiency causes substrate accumulation upstream and decreased product formation downstream, leading to metabolic blockades. | Think of a traffic jam in metabolic flow. |
| 20 | Explain the concept of enzyme isoforms and their significance. | Isoforms are different molecular forms of an enzyme catalyzing the same reaction, often tissue-specific, allowing fine-tuned regulation. | Different versions for different tissues. |
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