- 1. What property of the peptide bond makes it relatively unreactive under physiological conditions?
A) Hydrophobic interactions
B) Resonance stabilization
C) Ionic bonding
D) Hydrogen bonding
- 2. Compared to esters, how reactive is the peptide bond?
A) More reactive
B) Equally reactive
C) Less reactive
D) It has no reactivity
- 3. During a chemical reaction of a peptide bond, where does the electronegative atom usually attack?
A) Oxygen atom
B) Alpha carbon
C) Nitrogen atom
D) Carbonyl carbon
- 4. What is formed immediately after the carbonyl double bond is broken during a peptide bond reaction?
A) Tetrahedral intermediate
B) Amide salt
C) Peptide dimer
D) Amino acid chain
- 5. Which biological process follows the pathway of attacking the carbonyl carbon in a peptide bond?
A) Translation
B) Proteolysis
C) Replication
D) Transcription
- 6. N–O acyl exchange reactions are characteristic of which specific molecules?
A) Nucleotides
B) Lipids
C) Inteins
D) Ribosomes
- 7. What is the product called when a thiol attacks a peptide bond?
A) Thiacyclol
B) Azacyclol
C) Cyclol
D) Oxacyclol
- 8. What is the product called when a hydroxyl attacks a peptide bond?
A) Thiacyclol
B) Hydroxyl-peptide
C) Azacyclol
D) Oxacyclol
- 9. What is the product called when an amine attacks a peptide bond?
A) Azacyclol
B) Thiacyclol
C) Oxacyclol
D) Amine-cyclol
- 10. Which of the following is a general term for the molecules formed when a thiol, hydroxyl, or amine attacks a peptide bond?
A) Cyclol
B) Ester
C) Protease
D) Peptide
- 11. What is the wavelength range for peptide bond absorption?
A) 100–150 nm
B) 300–350 nm
C) 190–230 nm
D) 250–300 nm
- 12. What does the delocalisation of the nitrogen lone pair electrons give to the peptide group?
A) Full triple-bond character
B) Ionic bonding character
C) Partial double-bond character
D) Non-polar covalent character
- 13. What geometric shape does the partial double bond render the amide group?
A) Planar
B) Pyramidal
C) Linear
D) Tetrahedral
- 14. Which isomer is overwhelmingly preferred in most peptide bonds?
A) Gauche
B) Cis
C) Trans
D) Eclipsed
- 15. What is the approximate trans:cis ratio for most peptide bonds?
A) 10:1
B) 1000:1
C) 1:1
D) 100:1
- 16. What is the approximate trans:cis ratio for X-Pro peptide groups?
A) 500:1
B) 30:1
C) 5:1
D) 1000:1
- 17. What is the dihedral angle ω defined by?
A) Cα–C'–N–Cα
B) C–N–Cα–O
C) N–Cα–C'–O
D) Cα–N–C'–Cα
- 18. What is the value of ω for the cis isomer?
A) 270°
B) 0°
C) 180°
D) 90°
- 19. What is the value of ω for the trans isomer?
A) 45°
B) 90°
C) 180°
D) 0°
- 20. What is the approximate time constant (τ) for isomerization at room temperature?
A) 5 minutes
B) 20 seconds
C) 1 second
D) 10 milliseconds
- 21. What is the activation energy for the transition state ω=±90°?
A) 20 kJ/mol
B) 80 kJ/mol
C) 5 kJ/mol
D) 150 kJ/mol
- 22. Which enzymes catalyze the cis-trans isomerization of X-Pro peptide bonds?
A) Proteases
B) Polymerases
C) Peptidyl prolyl isomerases
D) Kinases
- 23. What is the typical time scale for conformational protein folding?
A) 1–2 hours
B) 10–100 s
C) 1–5 minutes
D) 10–100 ms
- 24. Why do X-Pro peptide groups have a different trans:cis ratio than other peptide bonds?
A) Symmetry between Cα and Cδ atoms makes isomers nearly equal in energy
B) They have a shorter bond length
C) They contain more hydrogen bonds
D) They are always found in the unfolded state
- 25. What effect can a nonnative isomer have on protein folding?
A) It can slow or prevent folding
B) It always accelerates folding
C) It has no effect on folding
D) It forces the protein into a linear chain
- 26. What type of chemical bond is a peptide bond?
A) Metallic bond
B) Amide covalent bond
C) Hydrogen bond
D) Ionic bond
- 27. What is another name used to distinguish a peptide bond from an isopeptide bond?
A) Eupeptide bond
B) Alpha bond
C) Dipeptide bond
D) Polypeptide bond
- 28. What is the name of the reaction that forms a dipeptide?
A) Condensation reaction
B) Reduction reaction
C) Hydrolysis reaction
D) Oxidation reaction
- 29. What molecule is produced during the formation of a peptide bond?
A) ATP
B) Oxygen
C) Water
D) Carbon dioxide
- 30. What is the chemical formula of the peptide bond group?
A) -CO-NH-
B) -NH-OH-
C) -CO-NH2-
D) -CO-OH-
- 31. What is the process of releasing a water molecule during bond formation called?
A) Hydration
B) Hydrolysis
C) Dehydration synthesis
D) Phosphorylation
- 32. What is the source of energy for peptide bond formation in organisms?
A) Heat
B) Water
C) ATP
D) Sunlight
- 33. Which cellular component produces proteins?
A) Mitochondria
B) Nucleus
C) Lysosomes
D) Ribosomes
- 34. What enzyme forms the peptide bond in glutathione?
A) Glutamate–cysteine ligase
B) Glutathione synthetase
C) Protease
D) Peptidase
- 35. How is a peptide bond broken?
A) Dehydration
B) Condensation
C) Synthesis
D) Hydrolysis
- 36. What is the approximate half-life of a peptide bond at 25 degrees Celsius?
A) 1000 to 2000 years
B) Seconds
C) 350 to 600 years
D) 1 to 10 years
- 37. What non-enzymatic factor can cause peptide bond hydrolysis?
A) Light exposure
B) pH shift
C) Conformational strain
D) Temperature increase
- 38. By what mechanism does conformational strain facilitate hydrolysis?
A) ATP consumption
B) Transition state stabilization
C) Ground-state destabilization
D) Increased activation energy
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