Endergonic reactions MCQs With Answer

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Endergonic reactions MCQs With Answer — This concise, SEO-friendly introduction helps B. Pharm students master endergonic reactions in thermodynamics and biochemical contexts. Learn clear definitions, the role of Gibbs free energy (ΔG), how ΔG°, temperature, entropy (ΔS) and enthalpy (ΔH) influence non-spontaneous processes, and how cells drive endergonic steps using ATP hydrolysis and reaction coupling. These practice MCQs focus on pharmaceutical relevance: drug metabolism, biosynthetic pathways, enzyme action, and practical calculations for ΔG and equilibrium. Designed for exam prep and deep conceptual understanding, this set reinforces core principles needed in pharmacology, biochemistry, and pharmaceutical thermodynamics. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. Which statement best describes an endergonic reaction?

  • It releases free energy and occurs spontaneously.
  • It requires an input of free energy and is non-spontaneous under standard conditions.
  • It always has a negative enthalpy change.
  • It cannot occur in biological systems.

Correct Answer: It requires an input of free energy and is non-spontaneous under standard conditions.

Q2. What is the sign of Gibbs free energy (ΔG) for an endergonic reaction under standard conditions?

  • Negative
  • Zero
  • Positive
  • Indeterminate without ΔH and ΔS

Correct Answer: Positive

Q3. Which expression relates Gibbs free energy change to enthalpy and entropy?

  • ΔG = ΔH + TΔS
  • ΔG = ΔH – TΔS
  • ΔG = ΔS – TΔH
  • ΔG = T(ΔH – ΔS)

Correct Answer: ΔG = ΔH – TΔS

Q4. How can an endergonic biochemical step proceed in a cell?

  • By decreasing temperature to make ΔG negative
  • By coupling to an exergonic reaction such as ATP hydrolysis
  • By increasing activation energy
  • By removing enzymes

Correct Answer: By coupling to an exergonic reaction such as ATP hydrolysis

Q5. Which of the following is true about ΔG° (standard free energy change)?

  • It depends on the actual concentrations of reactants and products in the cell.
  • It is measured when all reactants and products are at 1 M and standard state conditions.
  • It is always equal to the equilibrium constant K.
  • It is independent of temperature.

Correct Answer: It is measured when all reactants and products are at 1 M and standard state conditions.

Q6. The relationship between ΔG° and the equilibrium constant K is:

  • ΔG° = RT ln Q
  • ΔG° = -RT ln K
  • ΔG° = RT K
  • ΔG° = -TK ln R

Correct Answer: ΔG° = -RT ln K

Q7. For a reaction with K >> 1 at 298 K, what is the sign of ΔG°?

  • Positive
  • Zero
  • Negative
  • Depends on ΔH

Correct Answer: Negative

Q8. Which factor does NOT change the thermodynamic spontaneity (ΔG) of a reaction?

  • Concentration of reactants
  • Temperature
  • Presence of a catalyst
  • Pressure (for gases)

Correct Answer: Presence of a catalyst

Q9. The equation ΔG = ΔG° + RT ln Q indicates that:

  • ΔG is independent of reactant/product concentrations.
  • Q is the equilibrium constant.
  • Actual free energy change depends on reaction quotient Q.
  • ΔG° includes concentration terms for the current state.

Correct Answer: Actual free energy change depends on reaction quotient Q.

Q10. Which of the following best explains why ATP hydrolysis drives many endergonic reactions?

  • ATP hydrolysis has a highly positive ΔG°.
  • ATP hydrolysis is catalyzed by enzymes, making it faster.
  • ATP hydrolysis has a large negative ΔG° that, when coupled, makes the overall ΔG negative.
  • ATP increases the activation energy of the coupled reaction.

Correct Answer: ATP hydrolysis has a large negative ΔG° that, when coupled, makes the overall ΔG negative.

Q11. In pharmaceutical biosynthesis, an endergonic step could be favored by:

  • Removing product as it forms to shift equilibrium
  • Increasing the activation energy
  • Decreasing enzyme concentration
  • Maintaining product concentration high

Correct Answer: Removing product as it forms to shift equilibrium

Q12. Which statement is true about entropy (ΔS) in endergonic reactions?

  • A decrease in entropy always makes ΔG more negative.
  • An increase in entropy (positive ΔS) can help make an endergonic process spontaneous at higher temperatures.
  • Entropy does not affect spontaneity.
  • Entropy only matters for gas-phase reactions.

Correct Answer: An increase in entropy (positive ΔS) can help make an endergonic process spontaneous at higher temperatures.

Q13. A reaction has ΔH = +20 kJ/mol and ΔS = +100 J/mol·K. At 298 K, is the reaction endergonic or exergonic? (Use ΔG = ΔH – TΔS)

  • Endergonic because ΔG is positive
  • Exergonic because ΔG is negative
  • At equilibrium
  • Cannot determine without ΔG°

Correct Answer: Exergonic because ΔG is negative

Q14. Which term best distinguishes kinetic control from thermodynamic control?

  • ΔG° value
  • Activation energy and rate of formation
  • Equilibrium constant magnitude
  • Standard enthalpy only

Correct Answer: Activation energy and rate of formation

Q15. In the cell, which process is an example of an endergonic reaction driven by coupling?

  • ATP → ADP + Pi (hydrolysis)
  • Glucose + phosphate → glucose-6-phosphate (phosphorylation by ATP)
  • O2 + e- → O2- (reduction)
  • Spontaneous diffusion of a solute down its concentration gradient

Correct Answer: Glucose + phosphate → glucose-6-phosphate (phosphorylation by ATP)

Q16. Which measurement technique directly provides enthalpy change (ΔH) useful for thermodynamic analysis?

  • UV-visible spectroscopy
  • Calorimetry
  • HPLC retention time
  • Fluorescence anisotropy

Correct Answer: Calorimetry

Q17. For an endergonic drug-conjugation reaction in a metabolic pathway, what pharmaceutical strategy can make the reaction proceed?

  • Increase product concentration
  • Use enzymatic coupling to energetically favorable reactions
  • Remove catalyst to slow the reaction
  • Lower temperature to reduce ΔS contribution

Correct Answer: Use enzymatic coupling to energetically favorable reactions

Q18. Which of the following is NOT a way cells lower ΔG for a process?

  • Coupling to ATP hydrolysis
  • Using ion gradients (chemiosmotic coupling)
  • Using enzymes to alter ΔG
  • Removing products from the reaction site

Correct Answer: Using enzymes to alter ΔG

Q19. How does temperature influence an endergonic reaction where ΔS is positive?

  • Higher temperature makes ΔG more positive, less favorable.
  • Higher temperature makes ΔG more negative, more favorable.
  • Temperature has no effect if ΔH is zero.
  • Only pressure matters for biochemical reactions.

Correct Answer: Higher temperature makes ΔG more negative, more favorable.

Q20. Which equation describes the change in ΔG when reaction conditions deviate from standard?

  • ΔG = ΔG°
  • ΔG = ΔG° + RT ln Q
  • ΔG = -RT ln K only at equilibrium
  • ΔG = ΔH + ΔS

Correct Answer: ΔG = ΔG° + RT ln Q

Q21. In pharmacokinetics, a drug-receptor binding that is endergonic would require which of the following to occur biologically?

  • It would never occur in vivo.
  • Cofactor binding or conformational change coupled to favorable interactions.
  • Lowering physiological temperature drastically.
  • Increasing drug concentration beyond solubility limits.

Correct Answer: Cofactor binding or conformational change coupled to favorable interactions.

Q22. Which statement correctly contrasts endergonic and endothermic?

  • Endergonic refers to heat absorption; endothermic to free energy uptake.
  • Endergonic deals with free energy (ΔG), endothermic with heat/enthalpy (ΔH).
  • They are synonymous terms.
  • Endergonic always implies endothermic.

Correct Answer: Endergonic deals with free energy (ΔG), endothermic with heat/enthalpy (ΔH).

Q23. Which of the following represents a common cellular strategy to make an unfavorable step favorable?

  • Perform the step in isolation without enzymes
  • Couple the step to ATP hydrolysis or ion transport
  • Increase the Gibbs free energy of the reactants
  • Allow the reaction to go to completion slowly

Correct Answer: Couple the step to ATP hydrolysis or ion transport

Q24. If ΔG° for a reaction is +5 kJ/mol, what does that tell you about K at standard conditions?

  • K > 1
  • K = 1
  • K < 1
  • Cannot determine without temperature

Correct Answer: K < 1

Q25. Which parameter directly indicates whether a reaction mixture initially favors reactants or products?

  • ΔG° only
  • Reaction quotient Q compared to K
  • Enzyme concentration
  • Standard enthalpy ΔH°

Correct Answer: Reaction quotient Q compared to K

Q26. In coupled reactions, what must be true for the overall process to be spontaneous?

  • Sum of ΔG values must be positive.
  • Sum of ΔG values must be negative.
  • Each individual ΔG must be negative.
  • ΔH values must cancel out to zero.

Correct Answer: Sum of ΔG values must be negative.

Q27. Which of the following is a hallmark of an endergonic step in biosynthesis?

  • It often occurs without enzyme catalysis.
  • It commonly requires nucleotide triphosphates or other energy carriers.
  • It decreases cellular order.
  • It releases heat as the main driving force.

Correct Answer: It commonly requires nucleotide triphosphates or other energy carriers.

Q28. How does Le Chatelier’s principle apply to making an endergonic reaction proceed?

  • By adding more product to shift equilibrium toward reactants
  • By removing products to shift equilibrium toward product formation
  • By increasing temperature only for exothermic reactions
  • It does not apply to biochemical systems

Correct Answer: By removing products to shift equilibrium toward product formation

Q29. Which calculation correctly approximates ΔG° at 298 K for a reaction with K = 1000? (Use R = 8.314 J/mol·K)

  • ΔG° ≈ +17.1 kJ/mol
  • ΔG° ≈ -17.1 kJ/mol
  • ΔG° ≈ 0 kJ/mol
  • ΔG° ≈ -2.48 kJ/mol

Correct Answer: ΔG° ≈ -17.1 kJ/mol

Q30. Which of the following best describes the role of a catalyst in an endergonic reaction?

  • Catalyst makes the reaction spontaneous by changing ΔG
  • Catalyst lowers activation energy and increases rate but does not change ΔG
  • Catalyst increases ΔG to favor reactants
  • Catalyst is only relevant for exergonic reactions

Correct Answer: Catalyst lowers activation energy and increases rate but does not change ΔG

Q31. In a reaction where ΔH is negative and ΔS is negative, increasing temperature will:

  • Always make the reaction more spontaneous
  • Never affect spontaneity
  • Make the reaction less spontaneous at sufficiently high temperature
  • Convert endergonic to exergonic regardless of magnitude

Correct Answer: Make the reaction less spontaneous at sufficiently high temperature

Q32. Which is an example of an endergonic biological process essential for drug biosynthesis?

  • ATP hydrolysis
  • Protein synthesis (peptide bond formation)
  • Spontaneous diffusion of lipophilic drugs
  • Exergonic oxidative phosphorylation

Correct Answer: Protein synthesis (peptide bond formation)

Q33. How is ΔG° relevant to drug-receptor binding studies?

  • It directly gives the on-rate constant of binding.
  • It is related to the equilibrium association constant through ΔG° = -RT ln Kd (or Ka).
  • It indicates the mass of the drug required for binding.
  • It measures only enthalpic contributions.

Correct Answer: It is related to the equilibrium association constant through ΔG° = -RT ln Kd (or Ka).

Q34. A biochemical step with ΔG° = +7 kJ/mol can proceed in vivo if:

  • The reaction quotient Q is much less than K at cellular concentrations.
  • Temperature is reduced to 0 K.
  • No enzyme is present.
  • The reaction is isolated from other pathways.

Correct Answer: The reaction quotient Q is much less than K at cellular concentrations.

Q35. Which molecular change typically accompanies coupling that drives an endergonic chemical transformation?

  • Formation of a high-energy intermediate such as a phosphorylated substrate
  • Permanent increase in entropy of the enzyme
  • Loss of ATP without transfer of phosphate
  • Spontaneous oxidation of substrates

Correct Answer: Formation of a high-energy intermediate such as a phosphorylated substrate

Q36. In enzyme-catalyzed coupling, what is the role of a transient enzyme-bound intermediate?

  • It prevents the coupled reaction from occurring.
  • It stores and transfers the energy needed to drive the endergonic step.
  • It increases ΔG° of the overall process.
  • It permanently modifies the enzyme to a different conformation.

Correct Answer: It stores and transfers the energy needed to drive the endergonic step.

Q37. Which of the following best describes a biochemical example of an endergonic process driven by ion gradients?

  • Synthesis of ATP by ATP synthase (chemiosmotic coupling)
  • Spontaneous breakage of peptide bonds
  • Diffusion of oxygen into mitochondria
  • Hydrolysis of ATP in the cytosol

Correct Answer: Synthesis of ATP by ATP synthase (chemiosmotic coupling)

Q38. When designing assays to measure ΔG for drug-related reactions, which control is essential?

  • Measuring only reactant concentrations and ignoring products
  • Calibrating temperature and ionic strength to physiological conditions
  • Using arbitrarily chosen buffer without reporting conditions
  • Ensuring no enzyme present in all samples

Correct Answer: Calibrating temperature and ionic strength to physiological conditions

Q39. Which statement about ΔG and chemical equilibrium is correct?

  • At equilibrium ΔG is maximum.
  • At equilibrium ΔG = 0 and Q = K.
  • At equilibrium ΔG is always positive.
  • At equilibrium ΔG = ΔH.

Correct Answer: At equilibrium ΔG = 0 and Q = K.

Q40. For a drug activation step that is endergonic, which pharmaceutical approach could make activation feasible?

  • Couple activation to exergonic metabolic oxidation without enzymes
  • Design a prodrug that is converted by an enzyme coupled to ATP hydrolysis
  • Increase storage temperature to accelerate spontaneous activation
  • Ensure no cofactors are present

Correct Answer: Design a prodrug that is converted by an enzyme coupled to ATP hydrolysis

Q41. Which of the following changes would make ΔG for a reaction more negative?

  • Increasing the concentration of products
  • Decreasing the concentration of reactants
  • Decreasing Q (the reaction quotient)
  • Raising the standard free energy ΔG°

Correct Answer: Decreasing Q (the reaction quotient)

Q42. In a synthesis pathway, why might a cell invest ATP to drive an endergonic step rather than rely on high concentrations of reactants?

  • High reactant concentrations are energetically cheaper to maintain.
  • ATP coupling gives specificity and control and avoids osmotic/solubility problems from high reactant levels.
  • ATP is always abundant and free to use.
  • High reactant concentration has no practical limits in cells.

Correct Answer: ATP coupling gives specificity and control and avoids osmotic/solubility problems from high reactant levels.

Q43. Which thermodynamic quantity is directly measured by isothermal titration calorimetry useful in studying binding that may be endergonic overall?

  • ΔG only
  • ΔH directly, and ΔG/ΔS can be derived
  • Only Kd with no thermodynamic data
  • Activation energy of binding

Correct Answer: ΔH directly, and ΔG/ΔS can be derived

Q44. A pharmaceutical reaction has ΔG° = +12 kJ/mol. Which tactic will NOT help make the reaction proceed spontaneously in vitro?

  • Couple to a reaction with ΔG° = -20 kJ/mol
  • Remove product continuously
  • Raise temperature if ΔS is negative and large
  • Increase reactant concentrations to lower Q

Correct Answer: Raise temperature if ΔS is negative and large

Q45. Which of the following describes a scenario where ΔG becomes zero?

  • When standard free energy ΔG° is zero regardless of conditions
  • Only at absolute zero temperature
  • When the system has reached equilibrium (Q = K)
  • When no reaction can proceed due to lack of catalyst

Correct Answer: When the system has reached equilibrium (Q = K)

Q46. In metabolic control, what is the significance of a rate-limiting endergonic step?

  • It cannot be regulated by the cell.
  • It often serves as a control point regulated by allosteric effectors or covalent modification.
  • It always proceeds at maximum rate.
  • It is not important for pathway flux.

Correct Answer: It often serves as a control point regulated by allosteric effectors or covalent modification.

Q47. Which factor would most directly convert a non-spontaneous ΔG into a spontaneous process without changing temperature?

  • Adding a catalyst to lower activation energy
  • Coupling the reaction to an exergonic reaction such that combined ΔG is negative
  • Increasing the molecular weight of reactants
  • Using a buffer with a slightly different pH but same ionic strength

Correct Answer: Coupling the reaction to an exergonic reaction such that combined ΔG is negative

Q48. Which statement about the magnitude of ΔG and biological significance is correct?

  • Only the sign of ΔG matters; magnitude is irrelevant biologically.
  • Both sign and magnitude matter: small negative ΔG may be easily reversed; large negative ΔG is effectively irreversible in cellular context.
  • Large positive ΔG indicates spontaneous reaction in cells.
  • ΔG magnitude determines enzyme specificity directly.

Correct Answer: Both sign and magnitude matter: small negative ΔG may be easily reversed; large negative ΔG is effectively irreversible in cellular context.

Q49. Which is true about endergonic reactions in photosynthesis?

  • Light-driven electron transfer provides energy to make otherwise endergonic carbon fixation steps proceed.
  • Photosynthesis proceeds without any endergonic steps.
  • Light reduces entropy so carbon fixation becomes spontaneous without energy input.
  • ATP is not involved in making carbon fixation favorable.

Correct Answer: Light-driven electron transfer provides energy to make otherwise endergonic carbon fixation steps proceed.

Q50. Which best summarizes how pharmaceutical scientists exploit thermodynamics to design effective drug transformations involving endergonic steps?

  • Ignore ΔG and focus solely on kinetics.
  • Use coupling reactions, enzyme catalysis, and control of concentrations/conditions to favor desired products.
  • Rely on spontaneous endergonic reactions in formulation design.
  • Always decrease temperature to favor drug synthesis.

Correct Answer: Use coupling reactions, enzyme catalysis, and control of concentrations/conditions to favor desired products.

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