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3.2 Protein Structure β Test 1
Q1. How many different amino acid sequences are possible for a polypeptide 146 residues long?β (20)ΒΉβ΄βΆ
Q2. The predominant amino acid present in Ξ²-sheets is:β Glycine
Q3. The amino acid residue most abundant in water-soluble globular proteins is:β Serine
Q4. In Ξ±/Ξ²-barrel structures, the active site is usually located:β At the carboxy side of the strands
Q5. How many amino acid residues are present per turn of an Ξ±-helix?β 3.6
Q6. The amino acid that interrupts Ξ±-helix conformation by introducing kinks is:β Proline
Q7. Which amino acid is most likely to disrupt an Ξ±-helix?β Proline
Q8. Which amino acid cannot participate in Ξ±-helix conformation, introducing a destabilizing kink?β Proline
Q9. A 60-residue polypeptide forms a single contiguous Ξ±-helix. Its approximate length and mass are:β 90 Γ
, 6.6 kDa
Q10. The length and molecular mass of a 60-residue single Ξ±-helix are:β 90 Γ
, 6.6 kDa
Q11. The hydrogen bond in an Ξ±-helix can be represented as:β i β i+4
Q12. In an ideal Ξ±-helix, the carbonyl oxygen of residue i hydrogen-bonds to the amide hydrogen of residue:β i+4
Q13. For a 35-kDa Ξ±-helical protein (mean residue 110 Da, rise 1.5 Γ
/residue), the helix length is about:β 477 Γ
Q14. Which statement is FALSE for the Ξ±-helix of proteins?β Left-handed helices are common
Q15. The shortest stable Ξ±-helix detectable by circular dichroism is about how many residues?β 6
Q16. Why can Ξ²-barrel membrane structures NOT be predicted by simple hydropathy plots?β Alternating hydrophilic and hydrophobic residues in the sequence
Q17. The sequence βSer-Gly-Pro-Glyβ is most probably part of a:β Turn
Q18. The peptide unit between which residues has the highest chance of a cis configuration?β Gly, Pro
Q19. Which amino acid substitution is most likely to change a protein's tertiary structure?β Lys to Tyr
Q20. Which bond is responsible for the primary structure of a protein?β Covalent (peptide) bonds
Q21. Protein denaturation does NOT involve the breakage of:β Peptide bonds
Q22. Complete denaturation of an oligomeric protein by boiling for 5 minutes leads to disruption of:β Secondary, tertiary and quaternary
3.2 Protein Structure β Test 2
Q23. Complete denaturation of an oligomeric protein by boiling for 5 minutes leads to disruption of:β Secondary, tertiary and quaternary structures
Q24. Which statement is true regarding protein denaturation?β Fully denatured globular proteins resemble a random coil
Q25. Monomeric subunits of a dimeric protein are separated by Ξ²-mercaptoethanol. This indicates the subunits were held by:β Covalent (disulphide) bonding
Q26. Which interaction contributes the LEAST to stabilising the 3-D folding of a protein?β Ester bonds
Q27. The sequence βG-P-G-R-S-T-Gβ in a protein would most likely adopt a:β Loop
Q28. Which amino acid residue destabilizes an Ξ±-helix when inserted in the middle?β Pro
Q29. The amino acids known as helix breakers are:β Proline & Glycine
Q30. Which amino acids are known as helix breakers?β Proline & Glycine
Q31. Which amino acids are rarely present in an Ξ±-helix?β Glycine and proline
Q32. Which helix has an axial hole down its centre?β Ο-helix
Q33. The maximum number of backbone hydrogen bonds per residue is observed in:β Ξ±-helix
Q34. The buried interior (core) of a globular protein is predominantly made of which residues?β Apolar/hydrophobic
Q35. The major interaction stabilising overall protein structure is:β Hydrophobic interaction
Q36. Which residue is most likely found in the interior of a water-soluble globular protein?β Valine
Q37. How many disulphide bridges link chains A and B of human insulin?β Two
Q38. The specificity of a ligand-binding site on a protein is based on:β The amino acid residues lining the binding site
Q39. The most common and stable conformation for a polypeptide chain is the:β Ξ±-helix
Q40. Which bond in proteins has partial double-bond character?β CβN (peptide bond)
Q41. The peptide bond length between βCO and βNH is about:β 1.32 Γ
Q42. Like most acidβamide bonds, the peptide bond is stabilized by:β Ο-electron resonance
Q43. Which backbone torsion angle does NOT undergo rotation?β Ο (Omega, the peptide bond)
Q44. The two freely-rotatable backbone bonds (Greek-named angles) of the peptide backbone are:β Phi and Psi
3.2 Protein Structure β Test 3
Q45. If the Ο and Ο angles of a peptide are +60Β° and +45Β°, the structure is most likely a:β Left-handed Ξ±-helix
Q46. Polypeptides are best defined as:β Polymers of amino acids joined by peptide bonds
Q47. The Ο angle of an L-prolyl residue is ideally restricted to about:β β60Β°
Q48. The covalent configuration of a protein can only be altered by breaking which bond?β Disulphide bond
Q49. Which statement about stabilizing forces in proteins is correct?β Secondary to quaternary structure are maintained by non-covalent forces
Q50. Which statement is INCORRECT about protein structures?β Every part is a helix, strand or turn
Q51. Which are CORRECT about protein structure? P. Secondary structure = repeating backbone H-bond pattern; R. Quaternary = assembly of multiple subunitsβ P and R
Q52. Which statement concerning proteins is CORRECT?β Ξ±-helices are stabilized by H-bonds between carbonyl O and amide H
Q53. The surface of a globular protein is predominantly composed of which residues?β Polar
Q54. In the Ramachandran plot, Ο (psi) is the rotation angle about which bond?β CΞ±βC bond
Q55. Which best defines the quaternary structure of a protein?β Arrangement of two or more polypeptide subunits
Q56. Which interactions play a role in forming the quaternary structure of proteins?β Hydrogen bonds, disulphides, hydrophobic and electrostatic interactions
Q57. Which interactions play a role in quaternary structure?β Hydrogen bonds, disulphides, hydrophobic and electrostatic interactions
Q58. Ramachandran plots are derived from free rotation about which bond (Ο)?β CΞ±βC
Q59. Ramachandran plots are derived from free rotation about which bond?β CΞ±βC
Q60. In the Ramachandran plot (Ο vs Ο), Ο is the angle about the:β CΞ±βC bond
Q61. A Ramachandran plot describes the sterically allowed angles for which bonds?β CβCΞ± and CβN
Q62. A Ramachandran plot graphs the allowable combinations of which angles?β Ο and Ο
Q63. Which amino acid is preferred in a reverse turn?β Proline
Q64. In a reverse turn, the amino acids most often found are:β Proline and glycine
Q65. Which technique is NOT closely associated with determining protein secondary structure?β Protein fluorescence
Q66. Among conformations with potential energies β40, β50, β70, β30 kJ (C1βC4), the most stable is:β C3
3.2 Protein Structure β Test 4
Q67. An X-ray structure shows 40% helices and 40% Ξ²-strands. Its structural class is:β Ξ±/Ξ² (alpha-beta) class
Q68. The tertiary structure of a protein refers to:β The unique three-dimensional folding of the molecule
Q69. Which is an example of tertiary structure in a protein?β The complete fold of a single myoglobin chain
Q70. Which bond is NOT responsible for tertiary structure?β Covalent peptide bonds of the backbone
Q71. How is tertiary structure different from quaternary structure?β Tertiary is a single chain; quaternary has multiple chains
Q72. How is tertiary structure different from quaternary?β Tertiary is a single protein/peptide, quaternary has multiple peptides
Q73. The two principal backbone torsion angles of a polypeptide chain are:β Ο and Ο
Q74. The ideal trans peptide unit is characterized by an Ο angle of about:β Β±180Β°
Q75. Among interactions stabilising tertiary structure, the weakest is:β van der Waals interaction
Q76. Which amino acids are rarely present in an Ξ±-helix?β Glycine and proline
Q77. Which hydrogen bond type holds Ξ±-helices and Ξ²-sheets together?β NβH Β·Β·Β· O=C
Q78. Protein molecules that differ in only a few amino acid residues are called:β Isoforms
Q79. For the peptide Lys-Arg-Gln-Asp-Cys, which describes its peptide bonds?β Partial double-bond character and trans configuration
Q80. The backbone of a protein is constituted by:β Three torsion angles Ο, Ο and Ο
Q81. Which information specifies the three-dimensional shape of a protein?β The amino acid sequence
Q82. Which is an example of tertiary structure?β The complete fold of a single polypeptide
Q83. Which peptides result from trypsin cleavage of Met-Ala-Tyr-Met-Phe-Arg-Gly-Asp-Lys-Glu-Trp?β Met-Ala-Tyr-Met-Phe-Arg; Gly-Asp-Lys; Glu-Trp
Q84. A circular polymer of 38 arginine residues (Arg = 174 Da each) has a molecular weight of about:β 5928
Q85. How many different linear tripeptides can be made from three different L-amino acids, using each once?β 6
Q86. At a pH above its isoelectric point, a protein carries a:β Negative charge
Q87. For a protein of 100 amino acids, how many possible sequences exist?β 20ΒΉβ°β°