MCAT Biological and Biochemical Foundations of Living Systems Flashcards: 1a Enzyme Kinetics Regulation

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This deck focuses on 1a Enzyme Kinetics Regulation, giving you a quick way to review the definitions, rules, and examples that matter most for MCAT Biological and Biochemical Foundations of Living Systems.

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Work through these flashcards in short sessions. Try to answer each prompt before flipping the card, then revisit any cards you miss until the explanation feels automatic.

Flashcard 1: Which option describes a feedback inhibitor in a metabolic pathway?

Answer: End product inhibits an earlier enzyme, often the first committed step. Feedback inhibition regulates pathways by allosterically inhibiting upstream enzymes to prevent overproduction of end products.

Flashcard 2: State the relationship between $V_{max}$, $k_{cat}$, and total enzyme $[E]_T$.

Answer: $V_{max}=k_{cat}[E]_T$. V_max scales with total enzyme concentration, as k_cat is the turnover rate per enzyme molecule at saturation.

Flashcard 3: What is the definition of the turnover number $k_{cat}$?

Answer: Catalytic cycles per enzyme per second at saturation. k_cat quantifies an enzyme's efficiency by measuring product formation rate per active site when fully saturated.

Flashcard 4: What change in $K_m$ and $V_{max}$ is caused by pure noncompetitive inhibition?

Answer: $V_{max}$ decreases; $K_m$ unchanged. Noncompetitive inhibitors bind elsewhere, reducing effective enzyme concentration and thus V_max, without altering Km.

Flashcard 5: Identify where an uncompetitive inhibitor binds relative to substrate binding.

Answer: Only to the $ES$ complex (not to free enzyme). Uncompetitive inhibition requires substrate-bound enzyme, forming a dead-end complex that lowers apparent Km and V_max.

Flashcard 6: State the Michaelisnten equation for initial velocity $v$.

Answer: v=rac{V_{max}[S]}{K_m+[S]}. The equation describes hyperbolic kinetics, where velocity approaches V_max as [S] increases, based on enzyme-substrate binding equilibrium.

Flashcard 7: What is the approximate rate when [S]K_m?

Answer: vV_{max}. Enzyme saturation at high [S] limits the rate to V_max, independent of further increases in substrate concentration.

Flashcard 8: In a Lineweavernten plot, what is the $y$-intercept equal to?

Answer: rac{1}{V_{max}}. The y-intercept in the Lineweaver-Burk plot corresponds to infinite [S], where velocity equals V_max.

Flashcard 9: What is the defining feature of irreversible inhibition in enzyme kinetics?

Answer: Covalent or extremely tight binding permanently inactivates enzyme. Irreversible inhibitors form stable bonds with the enzyme, reducing active enzyme concentration permanently.

Flashcard 10: What is the approximate rate law when [S]K_m?

Answer: vrac{V_{max}}{K_m}[S]. This linear approximation derives from the Michaelis-Menten equation when [S] is much less than Km, simplifying to a first-order rate.

Flashcard 11: What is the definition of $V_{max}$ in Michaelis–Menten kinetics?

Answer: Maximum initial rate at saturating $[S]$. V_max is achieved when all enzyme active sites are saturated with substrate, reflecting the enzyme's maximum catalytic capacity.

Flashcard 12: Which inhibition type is best overcome by increasing $[S]$ (substrate concentration)?

Answer: Competitive inhibition. Increasing [S] can outcompete competitive inhibitors for the active site, restoring V_max unlike other inhibition types.

Flashcard 13: What is the definition of $K_m$ in Michaelis–Menten kinetics?

Answer: Substrate concentration where v=V_{max}. Km represents enzyme-substrate affinity, as it is the [S] at which half-maximal velocity is achieved in the Michaelis-Menten model.

Flashcard 14: What change in $K_m$ and $V_{max}$ is caused by uncompetitive inhibition?

Answer: $K_m$ decreases; $V_{max}$ decreases. Uncompetitive inhibitors bind only to ES complex, decreasing both Km and V_max by stabilizing the complex.

Flashcard 15: What does a Hill coefficient $n_H>1$ indicate about substrate binding?

Answer: Positive cooperativity. A Hill coefficient greater than 1 signifies enhanced binding affinity after initial substrate attachment in multimeric enzymes.

Flashcard 16: What is catalytic efficiency, and how is it written mathematically?

Answer: rac{k_{cat}}{K_m}. Catalytic efficiency measures how well an enzyme converts substrate to product at low [S], combining turnover and affinity.

Flashcard 17: What is the key kinetic hallmark of allosteric enzymes versus Michaelisnten enzymes?

Answer: Sigmoidal $v$ versus $[S]$ (cooperativity). Allosteric enzymes exhibit cooperative binding, yielding a sigmoidal curve unlike the hyperbolic Michaelis-Menten kinetics.

Flashcard 18: What is the effect of phosphorylation on enzyme activity in general terms?

Answer: Covalent modification that can increase or decrease activity. Phosphorylation adds a phosphate group via kinases, modulating enzyme conformation to either activate or inhibit catalysis.

Flashcard 19: In a Lineweavernten plot, what is the slope equal to?

Answer: rac{K_m}{V_{max}}. The slope reflects the ratio of Km to V_max, indicating how quickly velocity approaches maximum as [S] increases.

Flashcard 20: Which condition on $[S]$ makes the rate approximately zero-order in substrate?

Answer: [S]K_m. At high [S] relative to Km, the enzyme is saturated, making velocity independent of [S] and zero-order in substrate.

Flashcard 21: Identify where a competitive inhibitor binds relative to the substrate binding site.

Answer: Active site (mutually exclusive with substrate). Competitive inhibitors mimic substrate structure, binding reversibly to the same site and preventing substrate access.

Flashcard 22: What change in $K_m$ and $V_{max}$ is caused by competitive inhibition?

Answer: $K_m$ increases; $V_{max}$ unchanged. Competitive inhibitors compete for the active site, increasing apparent Km but not affecting V_max at high [S].

Flashcard 23: Which condition on $[S]$ makes the rate approximately first-order in substrate?

Answer: [S]K_m. At low [S] relative to Km, velocity is directly proportional to [S], following first-order kinetics in the Michaelis-Menten approximation.

Flashcard 24: In a Lineweavernten plot, what is the $x$-intercept equal to?

Answer: -rac{1}{K_m}. The x-intercept occurs where 1/v = 0, solving to -1/Km in the Lineweaver-Burk equation.

Flashcard 25: State the Lineweavernten (double-reciprocal) form of the Michaelisnten equation.

Answer: rac{1}{v}=rac{K_m}{V_{max}}rac{1}{[S]}+rac{1}{V_{max}}. The double-reciprocal plot linearizes Michaelis-Menten kinetics, allowing determination of Km and V_max from slope and intercepts.