Unit 3: Proteins and Enzymes - Practice Quiz

1 Based on their shape, proteins are broadly classified into fibrous and which other type?

2 Which of the following is an example of a fibrous protein?

3 The three-dimensional arrangement of a single polypeptide chain is called its:

4 Which level of protein structure refers to the linear sequence of amino acids?

5 The -helix and -pleated sheet are examples of which level of protein structure?

6 Which protein is primarily responsible for oxygen transport in blood?

7 Which of the following is a defensive function performed by proteins?

8 Which protein provides structural support and strength to skin, tendons, and bones?

9 Insulin is a protein that functions as a:

10 A Ramachandran plot is used to display the allowed values of which two dihedral angles?

11 The Ramachandran plot primarily helps identify which type of conformations for a polypeptide?

12 Which amino acid shows the greatest flexibility and occupies the widest region on a Ramachandran plot?

13 Denaturation of a protein primarily results in the loss of its:

14 Which of the following can cause denaturation of a protein?

15 Which type of bond remains intact during protein denaturation?

16 According to the international classification, enzymes are divided into how many main classes?

17 Enzymes that catalyze hydrolysis reactions belong to which class?

18 In the Michaelis-Menten equation, represents the substrate concentration at which the reaction velocity is:

19 Most human enzymes show maximum activity at an optimum temperature of approximately:

20 Enzymes speed up reactions primarily by:

21 A protein is found to contain multiple polypeptide chains held together by non-covalent interactions, giving rise to a functional oligomer. Which level of protein structure does this arrangement represent?

22 In an -helix, hydrogen bonds stabilizing the structure form between the C=O of one residue and the N–H group of which residue?

23 Keratin and collagen are commonly classified together based on their shape and solubility. Which category do they belong to?

24 Hemoglobin transports oxygen in the blood. Which functional class of proteins best describes this role?

25 A patient's immune response involves proteins that specifically recognize and bind foreign antigens. These proteins function primarily as:

26 The Ramachandran plot displays the allowed conformations of a polypeptide backbone. Which two angles are plotted against each other?

27 Which amino acid shows an unusually large allowed region in the Ramachandran plot due to the absence of a bulky side chain?

28 In a Ramachandran plot, right-handed -helices and antiparallel -sheets appear in distinct clusters. Why are certain regions of the plot considered disallowed?

29 During denaturation by heat, which of the following is typically disrupted while the primary structure remains intact?

30 Urea and guanidinium chloride are commonly used to denature proteins. They act mainly by:

31 Which type of covalent bond contributes to protein stability and can be reduced by agents such as -mercaptoethanol?

32 An enzyme catalyzes the transfer of a phosphate group from ATP to glucose. According to the EC classification, this enzyme belongs to which class?

33 Which enzyme class catalyzes the hydrolytic cleavage of bonds using water as a reactant?

34 An enzyme converts glucose-6-phosphate to fructose-6-phosphate without changing the molecular formula. This reaction is catalyzed by an:

35 For an enzyme obeying Michaelis–Menten kinetics, the is best described as the substrate concentration at which:

36 An enzyme has and . What is the reaction velocity when ?

37 In a Lineweaver–Burk (double reciprocal) plot, the y-intercept corresponds to:

38 Most enzymes show a bell-shaped curve of activity versus pH. This behavior is primarily because pH affects:

39 As temperature rises above an enzyme's optimum, reaction rate initially increases but then falls sharply. The decline is mainly due to:

40 The 'induced fit' model of enzyme catalysis differs from the 'lock and key' model because it proposes that:

41 In a Ramachandran plot, glycine residues occupy a substantially larger allowed region than other amino acids. Which structural feature best explains this?

42 Proline shows a highly restricted range of angles clustered near . What is the underlying reason?

43 An enzyme has and . At a substrate concentration of , what is the reaction velocity?

44 A competitive inhibitor is added to an enzyme reaction. On a Lineweaver-Burk plot, how do the intercepts change relative to the uninhibited reaction?

45 For an enzyme, and . What is the catalytic efficiency ?

46 An enzyme shows maximal activity at pH 7. Activity drops sharply on both sides of this optimum. Which explanation is most consistent with this bell-shaped curve?

47 In the serine protease chymotrypsin, which residues constitute the catalytic triad responsible for the nucleophilic attack?

48 Transition-state analogs are often extremely potent enzyme inhibitors. What is the fundamental reason?

49 An enzyme catalyzes the transfer of a phosphate group from ATP to glucose. Under the EC classification system, which class does it belong to?

50 Which enzyme class specifically catalyzes the joining of two molecules coupled to the hydrolysis of a nucleoside triphosphate?

51 Which statement most accurately describes the thermodynamics of protein folding under physiological conditions?

52 Urea and guanidinium chloride denature proteins primarily by which mechanism?

53 In the classic hierarchy (SCOP/CATH), what distinguishes an protein from an protein?

54 A right-handed -helix has a rise of per residue and residues per turn. What is the pitch (rise per turn) of the helix?

55 Hemoglobin exhibits a sigmoidal -binding curve while myoglobin is hyperbolic. The sigmoidal shape reflects which property?

56 For an enzyme obeying Michaelis-Menten kinetics, what fraction of is reached when ?

57 A noncompetitive inhibitor and a competitive inhibitor are compared. Which pair of effects on kinetic parameters is correct?

58 The proposed catalytic strategy in which an enzyme reduces the entropic cost of a reaction by binding substrates in the correct orientation is best described as:

59 Anfinsen's ribonuclease refolding experiment demonstrated which principle?

60 The binding of 2,3-bisphosphoglycerate (2,3-BPG) to hemoglobin has what functional consequence?