COMPETITIVE EXAM MCQs SERIES of LIFE SCIENCES for UGC-CSIR NET/JRF, SLET, GATE, and other entrance tests – MOLECULES AND THEIR INTERACTION RELEVANT TO BIOLOGY – Biophysical Chemistry Core Concepts.
Syllabus Outline
- Concepts of pH and pKa; Henderson-Hasselbalch equation
- Biological buffers – phosphate, bicarbonate, Tris buffer
- Thermodynamic principles – ΔG, ΔH, ΔS, equilibrium constant
- First- and second-order reaction kinetics
- Rate constants, reaction half-life, Arrhenius equation
- Colligative properties – boiling point elevation, freezing point depression
- Osmosis and osmotic pressure in biological systems
- Chemical equilibrium and Le Chatelier’s principle
This quiz contains concept-based, most frequently asked 25 MCQs of “MOLECULES AND THEIR INTERACTION RELEVANT TO BIOLOGY – Biophysical Chemistry Core Concepts”. Each question has a single correct/most appropriate answer.
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1. A buffer is most effective when [A⁻] = [HA]. Which statement best describes this using the Henderson–Hasselbalch equation?
A) pH = pKa + 1
B) log([A⁻]/[HA]) = 0
C) [A⁻]/[HA] = 0.1
D) Buffer is 50% titrated
2. Assertion (A): The bicarbonate buffer (H₂CO₃/HCO₃⁻) is the main extracellular buffer, though its pKa (6.1) ≠ is physiological pH (7.4).
Reason (R): It works as an open system regulated by CO₂ via respiration.
A) Both A and R are true; R explains A
B) Both true, R not explanation
C) A true, R false
D) A false, R true
3. A Tris buffer made at pH 7.4 (25°C, pKa = 8.07) is used at 37°C (pKa = 7.80). What happens to its pH?
A) > 7.4
B) < 7.4
C) = 7.4
D) < 7.4 followed by = 7.4
4. What is a major limitation of the Henderson–Hasselbalch equation for concentrated buffers?
A) Ignores temperature
B) Assumes zero ionic strength
C) Uses concentrations, not activities
D) Not valid for weak base buffers
5. Which condition defines a spontaneous process in thermodynamics?
A) ΔH < 0
B) ΔG < 0
C) ΔS < 0
D) ΔG > 0
6. A reaction has ΔH = +10 kJ/mol and ΔS = +50 J/mol·K. At what temperature does it become spontaneous?
A) Below 200 K
B) Above 200 K
C) At 200 K
D) Never
7. Enzyme activity doubles for every 10°C rise until denaturation. What is this effect called?
A) Q₁₀ effect
B) Arrhenius effect
C) Enthalpy shift
D) Van’t Hoff relation
8. For an enzyme, Vmax = 120 μmol/min and Km = 30 mM. At [S] = 30 mM, what is the velocity?
A) 120 μmol/min
B) 60 μmol/min
C) 90 μmol/min
D) 30 μmol/min
9. Competitive inhibition affects which parameter?
A) Vmax only
B) Km only
C) Both
D) Neither
10. In the Lineweaver–Burk plot, slope equals:
A) 1/Vmax
B) 1/Km
C) Km/Vmax
D) Vmax/Km
11. Noncompetitive inhibition changes:
A) Only Vmax
B) Only Km
C) Both
D) Neither
12. The turnover number (kcat) of an enzyme is:
A) Substrate converted per enzyme per second
B) Ratio of Km/Vmax
C) Amount of activation energy lowered per second in an enzyme-catalysed reaction
D) pH optimum
13. Enzyme-substrate binding is mainly stabilised by:
A) Covalent bonds and hydrophilic interactions
B) Hydrogen bonds and hydrophobic interactions
C) Ionic lattice and hydrophobic interactions
D) Hydrogen bonds, hydrophilic interactions and disulfide bonds
14. In allosteric enzymes, the effector binds to:
A) Catalytic site
B) Active site
C) Regulatory site
D) Substrate site
15. The Hill coefficient (n) indicates:
A) Enzyme turnover
B) Degree of cooperativity
C) pH sensitivity
D) Thermal stability
16. An enzyme shows sigmoidal kinetics. It likely has:
A) Single subunit
B) Cooperative binding
C) Competitive inhibitor
D) Denaturation
17. Which amino acid often acts as a proton donor/acceptor in enzyme active sites?
A) Glycine
B) Histidine
C) Valine
D) Cysteine
18. The Anfinsen experiment showed that:
A) Enzymes need chaperones to refold
B) Primary sequence of protein determines folding
C) Denaturation of protein is irreversible
D) Protein folding is an energy-intensive process and pathway mediated
19. The melting temperature (Tm) of a protein is:
A) The temperature at which denaturation starts
B) The temperature at which 50% protein is unfolded
C) The temperature at which 50% catalytic activity is lost
D) The temperature at which 50% protein melted
20. Membrane fluidity increases with:
A) More saturated fatty acids
B) Longer fatty acid chains
C) More unsaturated fatty acids
D) High cholesterol only
21. The transport of glucose by Na⁺-glucose symporter is an example of:
A) Passive diffusion
B) Facilitated diffusion
C) Secondary active transport
D) Primary active transport
22. The conversion of fructose-6-phosphate to fructose-1,6-bisphosphate occurs easily in cells despite a positive ΔG°. Why?
A) Enzyme makes the transition energy negative.
B) It’s coupled with ATP hydrolysis, giving overall negative ΔG.
C) High product concentration pushes the reaction forward.
D) Large entropy increase drives the reaction.
23. How do osmotic conditions affect cell blebbing and symmetry during animal cell division?
A) High osmolarity promotes symmetric division without spindle aid.
B) Low osmolarity increases early blebbing and leads to more symmetric cells.
C) Effects depend on the extracellular matrix stiffness, not osmotic pressure.
D) Hypertonic conditions make the cortex–membrane boundary more uniform, ensuring symmetry.
24. Assertion (A): Adding an inert gas at constant volume does not change the equilibrium position.
Reason (R): Inert gases raise total pressure, shifting the equilibrium toward fewer gas moles.
A) Both true; R explains A
B) Both true; R doesn’t explain A
C) A true; R false
D) A false; R true
25. Assertion (A): Freezing point depression is better for finding macromolecule molecular weight than osmotic pressure.
Reason (R): Osmotic pressure gives a stronger and more measurable effect per concentration.
A) Both true; R explains A
B) Both true; R doesn’t explain A
C) A true; R false
D) A false; R true
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References
- Nelson, David L. & Cox, Michael M. (2021). Lehninger Principles of Biochemistry, W. H. Freeman, 8th Edition
- Voet, Donald, Voet, Judith G., & Pratt, Charlotte W. (2018). Voet’s Principles of Biochemistry, Wiley, 5th Edition
- Berg, Jeremy M., Tymoczko, John L., & Stryer, Lubert (2023). Biochemistry, W. H. Freeman, 10th Edition
- Palmer, Trevor & Bonner, Philip L. (2007). Enzymes: Biochemistry, Biotechnology, Clinical Chemistry, Horwood Publishing, 2nd Edition
- Upadhyay, Avinash, Upadhyay, K., & Nath, Nirmalendu (2023). Biophysical Chemistry: Principles and Techniques, Himalaya Publishing House, 4th Edition
