Becker's World of the Cell 9th Edition by Lewis Kleinsmith, Jeff Hardin, Gregory Paul Bertoni

Exercise 8

Glycolysis and Gluconeogenesis. As Figure 9-11 indicates, gluconeogenesis is accomplished by what is essentially the reverse of the glycolytic pathway but with bypass reactions in place of the first, third, and tenth reactions in glycolysis.
(a)Explain why it is not possible to accomplish gluconeogenesis by a simple reversal of all the reactions in glycolysis.
(b)Write an overall reaction for gluconeogenesis that is comparable to Reaction 9-16 for glycolysis.
(c)Explain why gluconeogenesis requires the input of six molecules of nucleoside triphosphates (four ATPs and two GTPs)per molecule of glucose synthesized, whereas glycolysis yields only two molecules of ATP per molecule of glucose.
(d)Assuming concentrations of ATP, ADP, and P i are such that G for the hydrolysis of ATP is about 10 kcal/mol, what is the approximate G value for the overall reaction for gluconeogenesis that you wrote in part b
(e)With all of the enzymes for glycolysis and gluconeogenesis present in a liver cell, how does the cell "know" whether it should be synthesizing or catabolizing glucose at any given time