46. The following plot is for an enzyme with multiple ligand binding sites. Which statement is True for this enzyme? (x: ligand concentration; y: fractional saturation) 

(A) This enzyme is a non-allosteric oligomer.
(B) The Hill coefficient for this enzyme is 2.
(C) ligand binding favors another ligand binding.
(D) ligand binding disfavors another ligand binding.
(E) The Hill coefficient for this enzyme is -0.5.

42. Which chemical classification does proline belong to? (A) Amphipathic amino acid (B) Aromatic amino acid (C) Imino acid (D) Basic amino acid (E) Acidic amino acid

43. Which of the following metabolic enzymes is NOT directly regulated by the ATP level? (A) Pyruvate kinase M2 (B) Phosphofructokinase (C) Pyruvate dehydrogenase (D) Isocitrate dehydrogenase (E) a-Ketoglutarate dehydrogenase

44. A sample containing three proteins (A, B, and C) was analyzed by SDS-PAGE, as shown below. Size exclusion chromatography (also known as gel filtration) was utilized for their separation. Which protein will elute first through size exclusion chromatography? (A)A (B)B (C)C (D) It depends on the shape and oligomerization state of the proteins. (E) It depends on the isoelectric point (pI) of the proteins.

45. Which of the following statements accurately describes the Warburg effect? (A) It involves the preferential use of oxidative phosphorylation over glycolysis in cancer cells. (B) It describes the upregulation of gluconeogenesis in normal cells under hypoxic conditions. (C) It signifies the increased reliance of cancer cells on glycolysis, even in the presence of oxygen. (D) It indicates the decreased glucose uptake in tumors compared to healthy tissues. (E) The net effect is to increase the level of ATP.

47. The diagram depicts the mechanism of a protease inhibitor. What is the target of this inhibitor?  (A) Papain (B) Chymotrypsin (C) Pepsin (D) Carboxypeptidase A (E) Chymosin

48. Scientists covered an affinity chromatography column with microtubules for protein purification. Which of the following proteins would most likely be separated in this method? (A) Tubulin (B) Kinesin (C) Myosin (D) Actin (E) Lamin

49. Electrophoresis mobility shift assay (EMSA) is a sensitive method to detect protein-DNA interactions. The proteins and fluorescent DNA were combined as indicated and electrophoresed under native conditions, as shown below. Which of the following statements would be most likely?  (A) Protein B binds to the DNA independent of protein A. (B) Protein A binds to the DNA only in the presence of protein B. (C) Protein A and protein B compete for DNA binding. (D) Protein A and protein B form a protein complex before binding to the DNA. (E) Protein B binds to the protein A-DNA complex, resulting in a ternary complex.

50. Production of recombinant proteins in Escherichia coli is a common tool for research and industrial production of proteins. However, during affinity column purification, DnaK, unwanted contamination, is often coeluted with proteins of interest (POI). Which of the following statements about DnaK is TRUE? (A) DnaK binds to the charged regions of the POI and ADP can dissociate the interaction of Dnak with POI. (B) DnaK binds to the hydrophobic regions of the POI and ATP can dissociate the interaction of Dnak with POI. (C) DnaK binds to the polar regions of the POI and GTP can dissociate the interaction of Dnak with POI. (D) DnaK binds to the hydrophobic regions of the POI and GTP can dissociate the interaction of Dnak with POI. (E) DnaK binds to the charged regions of the POI and ATP can dissociate the interaction of Dnak with POI.

51. Based on the enzyme reaction plot shown below, which of the following statements is correct? (A) The of hexokinase IV for glucose is ~10 mM. (B) Hexokinase I works more efficiently than hexokinase IV when the blood glucose concentration is higher than 10 mM. (C) The of hexokinase I for glucose is ~5 mM. (D) Hexokinases catalyze a reaction that adds an AMP group to glucose. (E) At normal fasting conditions, hexokinase IV works better than hexokinase I .

52. Which of the following statements about the initial step of the reaction catalyzed by thermolysin is NOT correct? (A) The enzyme reaction involves the general acid-base catalysis. (B) A glutamate residue deprotonates water and promotes hydroxide attack on the carbonyl carbon of the substrate. (C) The ion stabilizes the buildup of negative charge on the peptide carbonyl oxygen. (D) Collapse of the unstable tetrahedral intermediate links the substrate to the glutamate residue covalently. (E) The enzyme is a member of hydrolases.