Allosteric enzyme regulation MCQs With Answer

Allosteric enzyme regulation MCQs With Answer

Understanding allosteric enzyme regulation is essential for B. Pharm students preparing for pharmacology and biochemistry exams. This concise guide covers mechanisms, models, kinetics, and physiological examples of allosteric control, emphasizing concepts like cooperative binding, homotropic and heterotropic effectors, MWC and KNF models, and pharmacological modulation. Questions focus on real enzymes (e.g., ATCase, PFK), regulatory sites, Hill coefficient interpretation, and implications for drug design. Each MCQ reinforces critical thinking about how modulators alter enzyme activity, metabolic flux, and therapeutic strategies. Ideal for revision and test practice, these questions deepen conceptual and applied knowledge in pharmaceutical contexts. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. Which model explains allosteric regulation by assuming concerted transitions between tense (T) and relaxed (R) states?

• Sequential (KNF) model
• Michaelis-Menten model
• Monod-Wyman-Changeux (MWC) model
• Induced-fit model

Correct Answer: Monod-Wyman-Changeux (MWC) model

Q2. A Hill coefficient greater than 1 indicates which of the following?

• Negative cooperativity
• No cooperativity
• Positive cooperativity
• Irreversible inhibition

Correct Answer: Positive cooperativity

Q3. Homotropic allosteric regulation involves which type of effector?

• A different molecule binding at a regulatory site
• The substrate itself acting as effector
• An irreversible covalent modifier
• A competitive inhibitor

Correct Answer: The substrate itself acting as effector

Q4. Which kinetic curve is characteristic of many allosteric enzymes with cooperative substrate binding?

• Hyperbolic Michaelis-Menten curve
• Linear dependence of velocity on substrate
• Sigmoidal velocity versus substrate concentration curve
• Parabolic inhibition curve

Correct Answer: Sigmoidal velocity versus substrate concentration curve

Q5. Where does an allosteric effector bind on an enzyme?

• Active site only
• Regulatory or allosteric site distinct from the active site
• At the peptide bond
• Only at the enzyme-substrate complex

Correct Answer: Regulatory or allosteric site distinct from the active site

Q6. Which of the following is an example of a heterotropic effector?

• Substrate acting on its own enzyme
• ATP acting on phosphofructokinase
• Salt concentration changes
• Temperature changes

Correct Answer: ATP acting on phosphofructokinase

Q7. Allosteric activators typically have which effect on enzyme kinetics?

• Decrease substrate affinity and reduce Vmax
• Increase substrate affinity and often increase catalytic efficiency
• Cause irreversible enzyme denaturation
• Convert enzyme into a non-functional monomer

Correct Answer: Increase substrate affinity and often increase catalytic efficiency

Q8. Aspartate transcarbamoylase (ATCase) is a classical example of an allosteric enzyme regulated by which nucleotide as a feedback inhibitor?

• ATP
• GTP
• CTP
• UTP

Correct Answer: CTP

Q9. Which statement best distinguishes allosteric inhibitors from competitive inhibitors?

• Allosteric inhibitors only bind the active site
• Competitive inhibitors are irreversible, allosteric inhibitors are reversible
• Allosteric inhibitors bind distinct regulatory sites and change enzyme conformation
• Competitive inhibitors increase Vmax

Correct Answer: Allosteric inhibitors bind distinct regulatory sites and change enzyme conformation

Q10. The KNF (sequential) model proposes what mechanism for cooperativity?

• All subunits switch simultaneously between T and R states
• Ligand binding induces conformational change in one subunit that sequentially affects neighbors
• Cooperativity arises solely from covalent modification
• Enzymes do not undergo conformational change

Correct Answer: Ligand binding induces conformational change in one subunit that sequentially affects neighbors

Q11. Which experimental plot is commonly used to estimate cooperativity via the Hill coefficient?

• Lineweaver-Burk plot
• Eadie-Hofstee plot
• Hill plot (log[v/(Vmax-v)] vs log[S])
• Scatchard plot

Correct Answer: Hill plot (log[v/(Vmax-v)] vs log[S])

Q12. Positive cooperativity in an enzyme requires which structural feature?

• Single polypeptide with no subunits
• Multiple interacting subunits or multiple binding sites
• Only a catalytic metal ion
• Irreversible covalent modification sites

Correct Answer: Multiple interacting subunits or multiple binding sites

Q13. Which of the following best describes heterotropic regulation?

• The substrate enhances its own binding
• A non-substrate molecule modulates enzyme activity by binding to a separate site
• Enzyme activity changes because of pH shift only
• Regulation occurs only through gene expression

Correct Answer: A non-substrate molecule modulates enzyme activity by binding to a separate site

Q14. How does a negative allosteric effector alter an enzyme’s activity curve?

• Shifts the sigmoidal curve to the left and increases steepness
• Converts a hyperbolic curve to sigmoidal with no shift
• Shifts the curve to the right, indicating decreased substrate affinity
• Causes the enzyme to follow zero-order kinetics

Correct Answer: Shifts the curve to the right, indicating decreased substrate affinity

Q15. Which enzyme is regulated allosterically by fructose 2,6-bisphosphate in glycolysis?

• Hexokinase
• Phosphofructokinase-1 (PFK-1)
• Pyruvate kinase
• Glucose-6-phosphatase

Correct Answer: Phosphofructokinase-1 (PFK-1)

Q16. What is the primary difference between allosteric regulation and covalent modification?

• Allosteric regulation is always irreversible while covalent modification is reversible
• Allosteric regulation involves noncovalent binding at regulatory sites; covalent modification involves chemical alteration of residues
• Covalent modification cannot affect enzyme activity
• Allosteric regulation changes gene expression

Correct Answer: Allosteric regulation involves noncovalent binding at regulatory sites; covalent modification involves chemical alteration of residues

Q17. Which of the following is an example of feedback inhibition by an allosteric mechanism?

• ATP activating pyruvate kinase
• End-product CTP inhibiting ATCase
• Substrate inhibition at high concentrations without a regulatory site
• Proteolytic cleavage of zymogens

Correct Answer: End-product CTP inhibiting ATCase

Q18. In drug design, why are allosteric modulators often advantageous?

• They always permanently inactivate enzymes
• They provide higher selectivity and can fine-tune activity without competing at the active site
• They bind irreversibly to DNA
• They are not affected by physiological concentrations of substrates

Correct Answer: They provide higher selectivity and can fine-tune activity without competing at the active site

Q19. A silent (neutral) allosteric ligand is characterized by what effect?

• It activates the enzyme strongly
• It has no effect on activity but can block other modulators
• It irreversibly inhibits the enzyme
• It increases enzyme expression levels

Correct Answer: It has no effect on activity but can block other modulators

Q20. Which technique can provide structural insights into allosteric conformational changes at high resolution?

• Mass spectrometry only
• X-ray crystallography or cryo-electron microscopy
• Paper chromatography
• UV-visible spectrophotometry alone

Correct Answer: X-ray crystallography or cryo-electron microscopy

Q21. Which statement best describes homotropic activation?

• A molecule unrelated to the substrate increases enzyme activity
• The substrate acts as an activator of its own enzyme, increasing affinity for additional substrate molecules
• Allosteric regulation requires phosphorylation
• It only occurs in monomeric enzymes

Correct Answer: The substrate acts as an activator of its own enzyme, increasing affinity for additional substrate molecules

Q22. Which parameter is least likely to be directly altered by an allosteric effector?

• Apparent Km (affinity)
• Cooperativity (Hill coefficient)
• Vmax under saturating conditions, in some cases
• Primary amino acid sequence of the enzyme

Correct Answer: Primary amino acid sequence of the enzyme

Q23. In the context of allosteric regulation, what does a Hill coefficient equal to 1 indicate?

• Positive cooperativity
• Negative cooperativity
• No cooperativity (independent binding sites)
• Irreversible inhibition

Correct Answer: No cooperativity (independent binding sites)

Q24. Which metabolic enzyme is regulated by both allosteric effectors and covalent phosphorylation?

• Hexokinase
• Glycogen phosphorylase
• Lactate dehydrogenase
• Glucose-6-phosphate dehydrogenase

Correct Answer: Glycogen phosphorylase

Q25. 2,3-Bisphosphoglycerate (2,3-BPG) is an allosteric effector for which oxygen-binding protein?

• Myoglobin
• Hemoglobin
• Catalase
• Carbonic anhydrase

Correct Answer: Hemoglobin

Q26. Which of the following best defines a regulatory subunit in an allosteric enzyme?

• A small molecule cofactor required for catalysis
• A protein subunit that binds effectors and modulates the catalytic subunit
• The enzyme’s prosthetic group
• A degradation signal for proteolysis

Correct Answer: A protein subunit that binds effectors and modulates the catalytic subunit

Q27. What is one major functional consequence of allosteric regulation in metabolic pathways?

• It prevents any change in metabolic flux
• It allows rapid, reversible control of pathway flux in response to cellular signals
• It always leads to irreversible enzyme activation
• It only affects enzyme synthesis at the gene level

Correct Answer: It allows rapid, reversible control of pathway flux in response to cellular signals

Q28. Which effector would most likely increase the activity of PFK-1 in an energy-depleted cell?

• High ATP concentration
• High citrate concentration
• Increased AMP concentration
• High levels of long-chain fatty acids

Correct Answer: Increased AMP concentration

Q29. Allosteric inhibitors that decrease apparent Vmax without affecting Km are best described as:

• Competitive inhibitors
• Noncompetitive-like allosteric inhibitors
• Uncompetitive inhibitors
• Substrate analogs that increase turnover

Correct Answer: Noncompetitive-like allosteric inhibitors

Q30. Which property distinguishes an allosteric enzyme from a typical Michaelis-Menten enzyme in pharmacological assays?

• Allosteric enzymes always show hyperbolic kinetics
• Allosteric enzymes often show sigmoidal kinetics and complex dose-response curves
• Michaelis-Menten enzymes are multimeric with cooperativity
• Allosteric enzymes cannot be inhibited by small molecules

Correct Answer: Allosteric enzymes often show sigmoidal kinetics and complex dose-response curves

Q31. Which of the following can act as a heterotropic inhibitor of a biosynthetic enzyme?

• Immediate substrate of that enzyme
• End product of the pathway
• Generic salt solution
• Denaturant like urea

Correct Answer: End product of the pathway

Q32. What role do conformational changes play in allosteric regulation?

• They are irrelevant; only chemical modification matters
• They transmit the effect of effector binding to the active site, altering activity
• They always cause enzyme degradation
• They only affect membrane-associated proteins

Correct Answer: They transmit the effect of effector binding to the active site, altering activity

Q33. Which of these is a common experimental approach to discover allosteric modulators in drug discovery?

• High-throughput screening of compound libraries for non-competitive modulation
• Only computational gene expression analysis
• Measuring protein melting temperature exclusively
• Antibody titer assays

Correct Answer: High-throughput screening of compound libraries for non-competitive modulation

Q34. Which statement about allosteric enzyme specificity is correct?

• Allosteric sites are always identical across all species
• Allosteric sites can confer greater specificity for small-molecule drugs than active sites
• Allosteric sites always overlap with the active site
• Allosteric sites cannot be targeted by pharmaceutical agents

Correct Answer: Allosteric sites can confer greater specificity for small-molecule drugs than active sites

Q35. Which enzyme involved in amino acid biosynthesis is regulated by feedback inhibition (allosteric) in bacteria?

• Threonine deaminase (regulated by isoleucine)
• Lactate dehydrogenase (regulated by pyruvate)
• DNA polymerase (regulated by nucleotides)
• Carbonic anhydrase (regulated by HCO3-)

Correct Answer: Threonine deaminase (regulated by isoleucine)

Q36. Which outcome best describes an inverse allosteric agonist (in receptor pharmacology) analogous to allosteric inhibition of enzymes?

• It binds and increases basal activity
• It binds to the allosteric site and reduces basal activity below constitutive levels
• It permanently activates the receptor
• It degrades the receptor protein

Correct Answer: It binds to the allosteric site and reduces basal activity below constitutive levels

Q37. Which factor can modulate allosteric regulation indirectly by altering enzyme quaternary structure?

• pH and ionic strength changes
• DNA methylation
• mRNA splicing only
• Chlorophyll concentration

Correct Answer: pH and ionic strength changes

Q38. In an allosteric enzyme, mutation of residues in the regulatory site is most likely to affect which property?

• Primary sequence of unrelated proteins
• Binding affinity for regulatory effectors
• The universal genetic code
• mRNA translation rate directly

Correct Answer: Binding affinity for regulatory effectors

Q39. Which statement about cooperative binding and substrate concentration is true?

• Cooperative enzymes respond gradually to substrate changes with no threshold behavior
• Cooperative enzymes can act as molecular switches showing a sharp response over a narrow substrate range
• Cooperativity eliminates sensitivity to substrate concentration changes
• Cooperativity only occurs at extremely low temperatures

Correct Answer: Cooperative enzymes can act as molecular switches showing a sharp response over a narrow substrate range

Q40. Which regulatory nucleotide acts as an allosteric activator of carbamoyl phosphate synthetase I in mammals?

• ATP
• GTP
• UTP
• N-acetylglutamate (NAG)

Correct Answer: N-acetylglutamate (NAG)

Q41. Uncompetitive inhibitors have which relationship with substrate binding, compared to many allosteric inhibitors?

• They bind only to free enzyme unlike many allosteric inhibitors
• They bind exclusively to the enzyme-substrate complex, reducing both Km and Vmax
• They increase Vmax while decreasing Km
• They are identical to homotropic activators

Correct Answer: They bind exclusively to the enzyme-substrate complex, reducing both Km and Vmax

Q42. Which structural technique can capture dynamic conformations of allosteric enzymes in solution?

• Static X-ray crystallography without complementary methods
• Nuclear magnetic resonance (NMR) spectroscopy
• Paper electrophoresis
• Simple light microscopy

Correct Answer: Nuclear magnetic resonance (NMR) spectroscopy

Q43. Allosteric activation that increases Vmax without changing substrate binding affinity is most similar to which type of kinetic effect?

• Competitive inhibition
• Pure catalytic activation increasing turnover number
• Uncompetitive inhibition
• Substrate depletion artifact

Correct Answer: Pure catalytic activation increasing turnover number

Q44. In an allosteric enzyme exhibiting negative cooperativity, increasing substrate concentration results in:

• Each additional substrate binding increases affinity for the next
• Each additional substrate binding decreases affinity for the next
• No change in binding affinity with subsequent substrate molecules
• Irreversible substrate binding only

Correct Answer: Each additional substrate binding decreases affinity for the next

Q45. Which of the following is NOT typically a goal when targeting allosteric sites for drug development?

• Achieve greater target selectivity
• Avoid competition with high endogenous substrate concentrations
• Completely block gene transcription of the enzyme
• Modulate activity subtly rather than full blockade

Correct Answer: Completely block gene transcription of the enzyme

Q46. Why might an allosteric inhibitor be effective even when substrate concentration is very high?

• Because it competes directly with substrate at the active site
• Because it alters enzyme conformation independently of substrate, reducing activity even at saturation
• Because it increases substrate turnover
• Because it degrades the substrate chemically

Correct Answer: Because it alters enzyme conformation independently of substrate, reducing activity even at saturation

Q47. Allosteric modulation can influence which aspects of enzyme function? Select the best summary.

• Only the rate of enzyme synthesis
• Substrate affinity, catalytic rate, and cooperativity
• Only the temperature sensitivity
• Only the enzyme’s solubility

Correct Answer: Substrate affinity, catalytic rate, and cooperativity

Q48. Which of the following enzymes shows allosteric regulation and is key in regulating glycolytic flux?

• Glucokinase exclusively
• Phosphofructokinase-1 (PFK-1)
• Alcohol dehydrogenase
• Ribonuclease

Correct Answer: Phosphofructokinase-1 (PFK-1)

Q49. Which biophysical measure directly reflects cooperative interactions among binding sites?

• The Michaelis constant Km only
• The Hill coefficient
• Optical density at 260 nm
• The isoelectric point of the enzyme

Correct Answer: The Hill coefficient

Q50. Which therapeutic strategy uses allosteric modulation rather than active-site inhibition to reduce side effects?

• Designing broad-spectrum active-site toxins
• Developing selective allosteric modulators that fine-tune activity
• Using high-dose non-specific enzyme inhibitors
• Increasing enzyme expression by gene therapy

Correct Answer: Developing selective allosteric modulators that fine-tune activity

G S Sachin

I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.

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