BIOL 141 Lecture Notes - Lecture 24: Glycolysis, Gout, Phosphofructokinase

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bluemosquito338

7 Dec 2017

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Describe the two forms of enzyme regulation, competitive inhibition and allosteric. Polymerase enzyme couples exergonic hydrolysis and endergonic condensation. Can make things that would be endergonic into exergonic by coupling a phosphorylation event. Increase probability of reaction between substrate and active site by forcing them together. Substrate binds to the enzyme at the active site. Binding causes the enzyme shape to change and forces substrate into the transition state conformation. Cell does not have to synthesize a new protein whenever each reaction is catalyzed. Allosteric activation: the active site becomes available to the substrates when a regulatory molecule binds to a different site on the enzyme. Regulatory molecule binds somewhere other than the active site and changes how the active site functions. Competitive inhibition: the substrate cannot bind when a regulatory molecule binds to the enzyme active site. Active site is occupied and substrate cannot bind. Has a similar shape and binds better than the substrate.

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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?

3) The hydrolysis of sucrose to glucose and fructose is exergonic. However, if you dissolve sucrose in water and keep the solution overnight at room temperature, there is no detectable conversion to glucose and fructose. Why?

Select one:

a. The change in free energy of the reaction is negative.

b. The activation energy of the reaction is high.

c. The free energy of the products is higher than the free energy of the reactants.

d. This is a condensation reaction.

e. The change in free energy of the reaction is positive.

5) Competitive inhibition differs from non-competitive inhibition in that the ___1___ site is where we see competitive inhibition, while the non-competitive inhibitor __2___.

1. a. allosteric b. non-active c. active d. hydrophillic e. hydrophobic

2.
a. binds to the active site, thus blocking it
b. binds outside the active site, changing the shape of the enzyme
c. binds outside the active site, and blocks the active site

6) Phosphofructokinase is an enzyme, and as such it __1___ of the reaction. It is part of glycolysis, and is an example of an enzyme controlled by inhibition, as high levels of citrate (an intermediate further down the catabolic pathway) turns the enzyme off
(1)Select one:
a. lowers activation energy
b. lowers the ÎG
c. raises the Free Energy
(2)Select one
a. non-competitivenegative feedback
b. irreversible competitivereversible competitive.

15)The reactions in the pathways of glycolysis and the citric acid cycle harvest the high-energy electrons stored in glucose. Therefore, these pathways _______________.

Select one:

a. take place in animal cells, but not in plant cells
b. are catabolic pathways
c. are anabolic pathways
d. involve the reduction of glucose and its metabolic intermediates

21) In an exergonic chemical reaction, the products have less free energy than the reactants (-ÎG). Endergonic reactions require an input of energy (+ÎG). The addition of starting materials and the removal of end products prevent metabolism from reaching final equilibrium. Instead, the cell exists in a state of dynamic equilibrium.

Select one:
True
False

greyferret515

Enzyme Activity

1. Briefly explain the principle of spectrophotometry.

2. Which of the following statements is true about enzymes?(check all correct answers)

		__ enzymes act on (are specific for) one or just a fewsubstrates
		__ enzymes can be denatured (loose their tertiary/quaternarystructure and activity) by extreme conditions such as heat, high orlow pH,or presence of organic solvents
		__most enzymes are DNA
		__ enzymes are protein
		__enzymes perform best at specific conditions of temperature, pHand salt concentration 5. Which enzymes break the following macromolecules? Match the following with their correponding answers: ___ Nucleic acids A. proteases or proteinases such as pepsin ___ Cellulose B. none ___ Triglycerides C. lipases ___ Proteins D. amylases ___ Starch E. nucleases 6.Match the following enzymes totheir products. Answers ___ pepsin, trypsin and other digestive proteases A.Nucleotides ___ salivary and pancreatic amylases and other enzymes B. AminoAcids ___ lipases C. Monosaccharides ___ nucleases D. fatty acids and glycerol 7. Based on experiments, what is the effect of extremeconditions of pH and temperature (boiling tube) on enzymeactivity? 8. ATP stores energy in the form of___ ___ Chemical energy ___ Kinetic energy ___ Thermal energy ___ Activation energy 9. An allosteric site in anenzyme is____ __ the site where reactions occur __ the site that binds aregulator __ the site that binds thesubstrate __ the site that binds the product 10. Enzymes increase the rate of reactions by making thetransition state less stable. __ True __ False 11. Enzymes increase the rate of reactions by placing reactingparts of the molecule in favorable positions. __ True __ False 12. Which of the followingis a mechanism for regulation of enzymes? __ covalent modification __ feedback inhibition __ allosteric regulation __ all of the above 13. Which of the following represents a correct order of eventsin an enzyme catalytic cycle? 1.enzyme changes shape 2.substrate binds to active site 3.substrate is converted to products 4. products are released from activesite __ 1>2>3>4 __ 2>1>3>4 __ 3>2>1>4 __ 2>4>3>1

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BIOL 141 Lecture Notes - Lecture 24: Glycolysis, Gout, Phosphofructokinase

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