Glycolysis

[Tanpopo]

I don't know if my answers are correct or not; are they detail enough? Can anyone take a look at them and give me some feedback? Especially questions 7 and 8. Thanks!

 

1) Is the conversion of 2-phosphoglycerate to phosphoenolpyruvate a redox reaction?

Ans: No, because there is no transfer of electrons.

 

2) Explain how fructose catabolism may lead to an overproduction of pyruvate relative to glucose metabolism in the liver.

Ans: PFK-1 is the major control step in glycolysis where many factors in glucose metabolism would regulate this step, but fructose could bypass PFK-1 to produce pyruvate.

 

3) Illustrate how increased intracellular [cAMP] affects the activity of pyruvate kinase in mammalian liver cells.

Ans: Low blood glucose --> Glucagon release --> increase cAMP --> activates PKA --> decrease glycogen synthesis

 

4) Ingestion of large amounts of ethanol inhibits glycolysis. Which glycolytic enzyme is inhibited? Why?

Ans: Lactate dehydrogenase is inhibited.

Because: Ethanol + NAD+ ---> CH3CHO + NADH + H+

Decrease [NAD+]/ [NADH] ratio, inhibit transformation of lactate to pyruvate.

 

5) In an anaerobic muscle preparation, lactate formed from glucose labeled in C-3 and C-4 would be labeled in __________

Ans: the methyl and carboxyl carbon atoms

 

6) A new dehydrogenase enzyme catalyzing the conversion of glyceraldehyde 3-phosphate to phosphoglycerate directly. How would modifying the glycolytic pathway in this way affect the cell?

Ans: It bypass a step; normally it would be:

GAP + Pi + NAD+ ----> 13BPG + NADH + H+ delta G = +6.3kJ/mol

1,3BPG + ADP ----> 3PG + ATP delta G = -18.5kJ/mol ==> delta G = -12.2kJ/mol

Bypassing the step that produce 13BPG, delta G could be more negative - more energy is produced.

 

7) State the fate of 32Pi that is added to a cell-free liver preparation undergoing glycolysis.

Ans: It will be used in early step to provide energy for starting glycolysis, then it will be regenerated at the end of glycolysis.

 

8) If patients with diabetes mellitus produce insufficient insulin, explain why these patients cannot properly respond to increases in the levels of blood glucose

Ans: High blood glucose ---> insulin secreation ---> Actived phosphatase ---> activate PFK2, inactivate FBPase-2 ----> increase [F-2,6BP] ---> Activate PFK 1, inactivate FBPase-1 ----> Increase glycolysis, decrease glyconeogensis

Patients with diabetes mellitus cannot produce sufficient insulin, therefore, glucose uptake is slow.