BCH 4054 Lecture Notes - Lecture 25: Allosteric Regulation, Phosphorylase, Dephosphorylation

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blushsquirrel211

31 Mar 2016

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Allosteric control- binding to a site other than the acive site. Allosteric control example- atpcase is inhibited by ctp and acivated by. This irst step of the reacion (allosteric control) catalyzes the reacion between carbonyl phosphate and aspartame. When the ctp concentraion increases, it decreases the rate of this reacion. When atp increases, it cause ctp to dissociate and to increase the producion of. This is a feedback mechanism tot control the amount of ctp present. Phosphorylaion brings and enzyme into an acive state. Dephosphorylaion brings and enzyme into an inacive state. Phosphorylase- use hpo4- top cleave a bond. Remove phosphate typically by hydrolysis of a phosphate ester bond. Muscle glycogen phosphorylase is an example of allosteric control. Phosphorylase a and when bound to serine, it is phosphorylase b. The formaion of phosphorylase a is covalently controlled. The making it acive or inacive is allosterically controlled. You will not be tested on drug design.

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Phosphofructokinase (PFK1) is a glycolytic enzyme that catalyzes the irreversible transfer of a phosphate from ATP to fructose -6-phosphate to form fructose-1, 6- bisphosphate.

fructose-6-phosphate + ATP --> fructose-1,6-bisphosphate + ADP

PFK1 is the key regulatory enzyme for glycolysis. When ATP levels are high in the cell, the cell no longer needs metabolic energy production to occur. In the case of these high energy levels, PFK1's activity is inhibited by allosteric regulation by ATP, which essentially closes the valve on the flow of carbohydrates through glycolysis.

Recall that allosteric regulators bind to a different site on the enzyme rather than the active (catalytic) site. ATP binds to the regulatory site and decreases PFK1 activity. ATP bound in the regulatory site acts as a modulator by lowering the affinity of PFK1 for its substrate, fructose-6-phosphate. AMP on the other hand, which is generated when the cell is in a low energy state binds to allosteric site and increases enzyme activity.

7. The enzyme PFK1 is an example of a non-regulatory enzyme or regulatory enzyme?

8. How is PFK regulated?

A. It is not regulated because it is a non-regulatory enzyme

B. allosteric enzyme regulation

C. covalent enzyme regulation

D. or proteolytic cleavage enzyme regulation?

9. What is the substrate and to which site on the enzyme does it bind? Which compounds are the positive and negative effectors?

10. In which conformational state would the enzyme be when negative inhibitors bind and in which conformational state would the enzyme be when positive inhibitors bind?

11. PFK1 is a heterotropic or homotropic regulatory enzyme?

12. Draw (or insert the picture from your course packet available on Canvas) the graph that corresponds to this reaction. Your graph should include the activity of PFK without bound effectors, with bound positive effector, and with bound negative effector. Label (or describe) each line to distinguish these along with which molecules are positive and negative effectors.

13. How does Vmax and K0.5 change with the positive and negative effectors?

BCH 4054 Lecture Notes - Lecture 25: Allosteric Regulation, Phosphorylase, Dephosphorylation

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