Glycolysis Practice Questions KEY PDF

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Prof: Dr. Pozzi...

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1 Practice Questions – Glycolysis (CH 18)

1. Draw the reaction that is catalyzed by Phosphoglucose isomerase. Label the structures.

2. Draw the structure of the enediol intermediate formed in the reaction catalyzed by PGI. a. Label the enediol structure such that you understand the arrangement of atoms involved in covalent bonds that give rise to the enediol intermediate. Enediol indicates two alcohol groups on either side of an C=C

b. Sometimes the enediols are referred to as enediolate. What does this mean? Enediolates are the ionized form of enediols, the difference between the two structures is the presence of protons 3. Why is it necessary for 2-PG to be converted to PEP prior to the synthesis of ATP? The standard free energy change for the hydrolysis of 2-PG is only about -16 kJ/mol, an insufficient amount of energy to drive synthesis of ATP. It is necessary to first convert 2-PG to the high energy PEP intermediate so that the phosphoryl group transfer from PEP to ADP forming pyruvate and ATP, where the energy harvested by the tautomerization of pyruvate is more than sufficient to drive ATP synthesis.

2 4. Consider the aspects of what is happening during the course of the reaction catalyzed by pyruvate kinase. Two events occur, the hydrolysis of the phosphate group of PEP to form pyruvate, followed by the tautomerization of the enol form of pyruvate to the keto form of pyruvate. Which of those events would you expect to be more exergonic and why? The tautomerization of pyruvate from keto to enol form has to be more exergonic and supply energy needed for ATP synthesis, otherwise hydrolysis of a phosphorylated compound would be sufficient – which it is not. Turns out hydrolysis of PEP to enol-pyruvate has a standard free energy change of -16 kJ/mol, whereas the tautomerization of enol-pyruvate to keto-pyruvate has a standard free energy change of -46 kJ/mol. 5. Which of the following enzymes does not catalyze a regulated step in glycolysis? a. Hexokinase b. Phosphofructokinase c. Phosphoglycerate Kinase d. Pyruvate Kinase e. All of the above catalyze a regulated step in glycolysis 6. Work through each of the reactions catalyzed by the enzymes above to show yourself why… All of the enzymes catalyze reactions that have larger, negative standard free energy changes. Phosphoglycerate kinase however liberates energy that helps promote/facilitate the reaction catalyzed by glyceraldehyde 3-phosphate dehydrogenase just prior. Recognize that these reactions are coupled, helping the glycolytic pathway to occur readily. All other enzymes are allosteric and able to have their activity regulated. 7. Consider the breakdown of the dissacharide sucrose. a. What are the monosaccharide components of sucrose?

b. Where would these enter into glycolysis? Glucose enters at glycolysis at the first step, being phosphorylated by hexokinase. Fructose either as DHAP or GA-3-P following reactions with Fructokinase and Fructose 1-Phophate Aldolase. (see and understand figure 18.23, pg 599) 8. Why is ethanol fermentation not a viable metabolic pathway in animals? The acetaldehyde product produced by the decarboxylation of PEP is toxic to cells (aka acetaldehyde is responsible for the feeling of being hungover )

3 9. Which of the following enzymes uses the cofactor TPP? a. Pyruvate Kinase b. Lactate Dehydrogenase c. Pyruvate Decarboxylase d. Alcohol Dehydrogenase e. None of the above 10. Why is TPP required for the reaction catalyzed converting Pyruvate to Acetaldehyde? TPP acts as a nucleophile to promote formation of acetaldehyde allowing for a favorable decarboxylation of pyruvate where a carbanion is not formed!...