Chapter 10 Regulatory Strategies 14 Blood clotting cascades are controlled by A) zymogen activation. D) All of the above. B) phosphorylation. E) None of the above. C) allosteric activation Ans:A Section:10.4 15 A regulatory mechanism that is NOT readily reversible: A) phosphorylation D) All of the above. B) allosteric control E) None of the above. C) proteolytic cleavage Ans:C Section:Introduction Short-Answer Questions 1 What is the function of aspartate transcarbamoylase? Ans:The enzyme catalyzes the first step in the synthesis of pyrimidines.It condenses carbamoyl phosphate and aspartate to form N-carbamoylaspartate and inorganic phosphate. Section:10.1 2 Give several examples of enzymes and proteins that are activated by proteolytic activation. Ans:Examples include digestive enzymes (trypsin),hormones(insulin),clotting enzymes (fibrinogen),developmental process proteins(collagen),and apoptosis proteins (caspases). Section:Introduction and 10.4 3 Why was it surprising to find that CTP inhibits ATCase? Ans:The substrates for ATCase are carbamoyl phosphate and aspartate.These molecules do not resemble CTP.Thus,it was clear that the CTP must not bind to the active site,but to a distinct regulatory site. Section:10.1 4 Do allosteric enzymes follow traditional Michaelis-Menten kinetics?Draw a graph of rate relative to substrate concentration for ATCase and compare it to Michaelis-Menten enzyme. Ans:No,ATCase displays different kinetics.A plot of rate versus substrate concentration is a sigmoidal curve,as opposed to the simple hyperbolic curve obtained by enzymes displaying Michaelis-Menten kinetics. Section:10.1 and Figure 10.15 5 How does the sequential model differ from the concerted model for allosteric enzymes? Ans:The concerted model does not allow for anything other than an"all-or-none"complete tense-or relaxed-form protein.In contrast,the sequential model allows for a mixed type of protein,containing some tense and some relaxed subunits.The form is in response to the ligand binding by a particular subunit. Section:10.1Chapter 10 Regulatory Strategies 5 14 Blood clotting cascades are controlled by A) zymogen activation. D) All of the above. B) phosphorylation. E) None of the above. C) allosteric activation. Ans: A Section: 10.4 15 A regulatory mechanism that is NOT readily reversible: A) phosphorylation D) All of the above. B) allosteric control E) None of the above. C) proteolytic cleavage Ans: C Section: Introduction Short-Answer Questions 1 What is the function of aspartate transcarbamoylase? Ans: The enzyme catalyzes the first step in the synthesis of pyrimidines. It condenses carbamoyl phosphate and aspartate to form N-carbamoylaspartate and inorganic phosphate. Section: 10.1 2 Give several examples of enzymes and proteins that are activated by proteolytic activation. Ans: Examples include digestive enzymes (trypsin), hormones (insulin), clotting enzymes (fibrinogen), developmental process proteins (collagen), and apoptosis proteins (caspases). Section: Introduction and 10.4 3 Why was it surprising to find that CTP inhibits ATCase? Ans: The substrates for ATCase are carbamoyl phosphate and aspartate. These molecules do not resemble CTP. Thus, it was clear that the CTP must not bind to the active site, but to a distinct regulatory site. Section: 10.1 4 Do allosteric enzymes follow traditional Michaelis-Menten kinetics? Draw a graph of rate relative to substrate concentration for ATCase and compare it to Michaelis-Menten enzyme. Ans: No, ATCase displays different kinetics. A plot of rate versus substrate concentration is a sigmoidal curve, as opposed to the simple hyperbolic curve obtained by enzymes displaying Michaelis-Menten kinetics. Section: 10.1 and Figure 10.15 5 How does the sequential model differ from the concerted model for allosteric enzymes? Ans: The concerted model does not allow for anything other than an “all-or-none” complete tense- or relaxed-form protein. In contrast, the sequential model allows for a mixed type of protein, containing some tense and some relaxed subunits. The form is in response to the ligand binding by a particular subunit. Section: 10.1