Unit 2: Protein chemistry - Practice Quiz

1 Which of the following is the primary function of enzymes as proteins?

2 Hemoglobin is an example of a protein that primarily functions in:

3 Which type of protein provides structural support in tissues such as skin, tendons, and bone?

4 Antibodies are proteins that function mainly in:

5 The primary structure of a protein refers to:

6 Which level of protein structure describes local folding patterns such as -helices and -sheets?

7 The quaternary structure of a protein is defined by:

8 Which type of bond primarily stabilizes the secondary structure of proteins?

9 The complete three-dimensional shape of a single folded polypeptide chain is called its:

10 The torsional angle around the bond in a protein backbone is denoted by:

11 A Ramachandran plot is used to display allowed combinations of which two angles?

12 The torsional angle (psi) describes rotation about which backbone bond?

13 The peptide bond ( angle) is usually found to be:

14 The rigidity of the peptide bond is due to its:

15 Circular Dichroism (CD) spectroscopy measures the differential absorption of:

16 In the far-UV region, CD spectroscopy is mainly used to determine the:

17 An -helical protein typically shows a characteristic CD spectrum with:

18 CD spectroscopy can detect protein secondary structure because proteins are:

19 The process by which a protein loses its native structure due to heat or chemicals is called:

20 Which interaction is considered a major driving force for protein folding in aqueous solution?

21 In a Ramachandran plot, the fully allowed region for right-handed -helices corresponds approximately to which combination of backbone dihedral angles?

22 Why does glycine occupy a uniquely broad region of allowed space in the Ramachandran plot compared to other amino acids?

23 The peptide bond dihedral angle is usually restricted to approximately . What is the primary reason for this restriction?

24 A protein CD spectrum in the far-UV region shows two negative minima at nm and nm and a positive maximum near nm. Which secondary structure dominates?

25 Circular dichroism measures which physical quantity as a function of wavelength?

26 Why is the far-UV region (– nm) most informative for determining protein secondary structure by CD?

27 Which level of protein structure is defined solely by the linear sequence of amino acids connected by peptide bonds?

28 The clustering of nonpolar side chains in the interior of a globular protein, away from water, is the primary organizing force for which structural level?

29 Hemoglobin consists of two and two subunits assembled into a functional tetramer. This arrangement is an example of which structural level?

30 In an antiparallel -sheet, the hydrogen bonds between strands are best described as:

31 An enzyme's catalytic activity is abolished when a single active-site histidine is mutated to alanine, though the protein still folds normally. This best illustrates that:

32 The binding of oxygen to one subunit of hemoglobin increases the oxygen affinity of the remaining subunits. This behavior is termed:

33 A structural protein such as collagen relies on which feature to achieve high tensile strength?

34 Which statement best explains the specificity of an enzyme for its substrate under the induced-fit model?

35 The dominant thermodynamic driving force for the folding of a globular protein in aqueous solution is:

36 The net free energy of stabilization () for a typical folded protein is only about – kcal/mol. What does this small value imply?

37 Levinthal's paradox highlights that proteins cannot fold by randomly sampling all conformations. The resolution most widely accepted is that:

38 A protein is heated and its CD signal at nm gradually disappears with a sharp sigmoidal transition. This observation indicates:

39 Adding a high concentration of urea to a protein solution typically causes unfolding because urea:

40 A CD spectrum showing a single broad negative minimum near nm and a positive band near nm is most consistent with which secondary structure?

41 In a Ramachandran plot, glycine occupies regions forbidden to other residues. Which combination of values would be sterically allowed for glycine but strongly disfavored for L-alanine?

42 A protein shows a far-UV CD spectrum with double minima at 208 nm and 222 nm and a maximum near 190 nm. Upon heating, the 222 nm signal approaches zero and a single deep minimum near 200 nm appears. What is the correct interpretation?

43 For a two-state folding equilibrium, the fraction folded is 0.90 at 25°C. If where , what is the approximate of unfolding at this temperature ( kJ/mol)?

44 The Anfinsen ribonuclease refolding experiment demonstrated a key principle, but reoxidation in the presence of a scrambling agent (urea + trace mercaptoethanol) initially gave only ~1% activity. What does this observation establish?

45 The peptide bond torsion angle is typically restricted to ~180° (trans). For which residue is the cis conformation () most frequently observed, and why?

46 The hydrophobic effect is the dominant driving force in protein folding. At room temperature, its favorable contribution is primarily driven by:

47 Near-UV CD (250–320 nm) of a protein probes tertiary structure through aromatic and disulfide chromophores. A protein retains full far-UV CD signal but loses all near-UV CD signal upon mild denaturation. This is the signature of:

48 Hemoglobin's cooperative binding is described by the Hill equation. If a Hill plot yields a slope for a tetramer, what is the correct interpretation?

49 In a parallel -sheet versus an antiparallel -sheet, the hydrogen bonding geometry differs. Which statement correctly distinguishes them?

50 In nucleic acids, the glycosidic torsion angle distinguishes syn and anti conformations. Which statement about B-DNA and Z-DNA is correct?

51 Cold denaturation of proteins occurs at low temperatures where becomes negative. This counterintuitive phenomenon arises because:

52 The mean residue ellipticity at 222 nm can estimate helix content. If a fully helical reference gives deg·cm²·dmol⁻¹ and a sample gives , what is the approximate helical fraction (ignoring coil baseline)?

53 An enzyme follows Michaelis–Menten kinetics with and M. A competing enzyme has and M. At very low substrate concentration (), which enzyme is catalytically more efficient?

54 Levinthal's paradox argues that random conformational search cannot explain folding times. The modern resolution invokes a folding funnel. Which statement best captures this concept?

55 A helix differs from an -helix. Which pair of features correctly characterizes the helix relative to the -helix?

56 The dihedral angles (about N–C) and (about C–C) define backbone conformation. For an idealized right-handed -helix, which approximate values apply?

57 Allosteric regulation is often described by the MWC (concerted) model. A key prediction of the MWC model that distinguishes it from the KNF (sequential) model is that:

58 A protein has kJ/mol and kJ·mol⁻¹·K⁻¹ for unfolding (assumed T-independent). Estimate its melting temperature (where ).

59 CD signals arise from differential absorption of left- and right-circularly polarized light by chiral chromophores. In far-UV protein CD, the dominant chromophore giving secondary-structure information is:

60 Quaternary structure stabilization frequently relies on buried interface area. In a domain-swapped dimer, the mechanism of oligomerization is best described as: