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 – Protein Folding and Structure Guide.
Syllabus Outline
- Primary, secondary, tertiary, and quaternary structures of proteins
- Alpha-helix and beta-sheet – hydrogen bonding, stability
- Turns and loops – role in protein flexibility
- Ramachandran plot – allowed regions, steric hindrance
- Protein domains – structural and functional units
- Common motifs and folding patterns
- Protein folding pathways – chaperones and folding intermediates
- Misfolding and diseases – prions, amyloidosis
This quiz contains concept-based, most frequently asked 25 MCQs of “MOLECULES AND THEIR INTERACTION RELEVANT TO BIOLOGY – Protein Folding and Structure Guide”. Each question has a single correct/most appropriate answer.
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1. Which statement correctly describes the strength of non-covalent interactions?
A) Hydrogen bonds are stronger in water than in nonpolar solvents.
B) Ionic bonds provide little stabilisation inside proteins due to the high dielectric constant.
C) Van der Waals forces are stronger than hydrogen bonds in protein interiors due to close association.
D) Hydrophobic interactions are mainly enthalpy-driven from stable nonpolar contacts.
2. Which interactions mainly stabilise protein quaternary structure?
A) Disulfide bonds.
B) Peptide and intramolecular H-bonds.
C) Hydrophobic interactions and salt bridges.
D) Intermolecular van der Waals forces.
3. A recurring β–α–β unit (X) and a 150-residue independently folding ATP-binding segment (Y) are found. Identify X and Y.
A) X: domain; Y: motif.
B) X: motif; Y: domain.
C) Both are motifs.
D) X: repeat; Y: loop.
4. Assertion (A): Disulfide bonds stabilise secondary structure.
Reason (R): They are covalent links between cysteine residues.
A) Both true; R explains A.
B) Both true; R doesn’t explain A.
C) A true; R false.
D) A false; R true.
5. Assertion (A): Glycine occurs in less favourable regions of the Ramachandran plot.
Reason (R): Its small side chain allows free rotation.
A) Both true; R explains A.
B) Both true; R doesn’t explain A.
C) A true; R false.
D) A false; R true.
6. Which statements about peptide bond geometry are correct?
I – Peptide bond is planar.
II – Trans is favoured over cis.
III – Cis X–Pro occurs frequently.
IV – ω angle strictly 0° or 180°.
A) I, II and IV
B) I, II, III and IV
C) I, II and III
D) II and III
7. H-bonds in an α-helix are:
A) Inter-strand, parallel to the chain axis.
B) Inter-strand, perpendicular to the axis.
C) Intramolecular, parallel to the axis.
D) Intramolecular, perpendicular to the axis.
8. Which describes the molten globule state?
A) No secondary structure, stable tertiary.
B) Native-like secondary, flexible tertiary.
C) Unfolded with disulfide bonds.
D) Aggregated cross-β state.
9. The folding funnel model shows that:
A) Folding follows one fixed path.
B) Native state is kinetically trapped.
C) Folding is entropically unfavourable and energy-driven.
D) Proteins sample many conformations biased toward the native state.
10. Hydrophobic effect in folding is driven by:
A) Strong van der Waals forces.
B) Entropy gain of released water.
C) Enthalpy drop from H-bonds.
D) Kinetic relaxation energy.
11. Assertion (A): The Molten globule state unfolds easily under mechanical force.
Reason (R): It has flexible tertiary contacts and a large transition distance.
A) Both true; R explains A.
B) Both true; R doesn’t explain A.
C) A true; R false.
D) A false; R true.
12. All amyloid fibrils share which common structural motif?
A) Random coil
B) α-helices
C) Cross-β sheets
D) Disulfide dimers
13. Prion infectivity arises because:
A) DNA integration occurs.
B) PrPˢᶜ converts PrPᶜ to the misfolded form.
C) Aggregates form pores.
D) Chaperones are sequestered.
14. In a Thioflavin T fluorescence assay, seeding with 5% preformed fibrils typically results in:
A) Loss of lag phase
B) Prolonged lag phase
C) Reduced final fluorescence intensity
D) Linear aggregation kinetics
15. Which are true for GroEL/GroES function?
I – ATP hydrolysis controls cycling.
II – ATP binding promotes GroES attachment.
III – Substrate release is spontaneous.
IV – GroES seals the folding chamber.
A) I, III and IV
B) I, II and IV
C) II and III
D) I and II
16. Mutation of conserved Pro → Gly in active site loop likely causes:
A) Rigid loop.
B) Increased flexibility.
C) α→β conversion.
D) Disulfide disruption.
17. A mutation that shifts the guanidinium hydrochloride unfolding midpoint to a higher concentration indicates:
A) Decreased protein stability
B) Stabilisation of the unfolded state
C) Faster unfolding kinetics
D) Increased protein stability
18. Which residue fits the strained β-boundary regions best?
A) Trp
B) Gly
C) Pro
D) Val
19. Hsp90 mainly acts by:
A) Preventing aggregation of new chains.
B) Sealing substrates in chambers.
C) Catalysing peptide bond formation.
D) Maintaining near-native substrates until activation.
20. Which force disappears in a vacuum?
A) Hydrophobic effect
B) van der Waals
C) Disulfide
D) Peptide
21. A 100-residue ATP-binding domain classifies proteins based on:
A) Sequence motifs
B) Function/fold
C) Dihedral distribution
D) Hydrodynamic radius
22. Most φ/ψ space is forbidden due to:
A) Bond rotation barriers.
B) H-bond limits.
C) Electrostatic repulsion.
D) Steric hindrance.
23. Why do D-amino acids occupy the right side (positive φ) of the Ramachandran plot while L-amino acids occupy the left side (negative φ)?
A) D-amino acids have a different peptide bond geometry
B) The Cβ atom’s position relative to the backbone creates different steric clashes
C) D-amino acids form weaker hydrogen bonds
D) The amide plane rotates in the opposite direction
24. A synthetic polypeptide containing only D-amino acids is analysed by circular dichroism (CD) spectroscopy and shows a characteristic helical structure. Compared to an L-amino acid α-helix, what difference would you observe?
A) The CD spectrum would show identical peaks at the same wavelengths
B) The CD spectrum would show mirror-image peaks
C) The structure would be unstable and show a random coil spectrum
D) No helical structure would form with D-amino acids
25. Levinthal’s paradox suggests that random conformational search would take ~10²⁷ years for a 100-residue protein. Yet proteins fold within seconds. How is this possible?
A) Folding is a random search accelerated by thermal motion
B) Disulfide bonds form first and guide folding
C) Chaperones dictate the correct folding pathway
D) Folding follows a funnel-shaped energy landscape with gradual stabilisation
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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
