41. Which of the following statements concerning receptor enzymes is CORRECТ ? (A) They are not usually membrane-associated proteins. (B) They contain an enzyme activity that acts upon acytosolic substrate. (C) They contain an enzyme activity that acts upon the extracellular ligand. (D) They have a ligand-binding site on the cytosolic side of the membrane. (E) They have an active site on the extracellular side ofthe membrane.

1. Compare the two reaction coordinate diagrams below and select the answer that correctly describes their relationship. In eachcase, the single intermediate is the ES complex.Free energy, (A) Diagram (a) describes a strict "lock and key" model, whereas diagram (b) describes a transition-state complementarity model. (B) The activation energy for the catalyzed reaction is #5 in diagram (a) and is #7 in diagram (b). (C) The activation energy for the uncatalyzed reaction is given by #5 + #6 in diagram (a) and by #7 + #4 in diagram (b). (D) The contribution of binding energy is given by #5 in diagram (a) and by #7 in diagram (b). (E) The ES complex is given by #2 in diagram (a) and #3 in diagram (b).

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