Problem Set 5

1)                  Is the Phosphofructokinase reaction in muscle more or less exergonic than under standard conditions, given the following concentrations:

Fructose-6-phosphate

1.0 mM

Fructose-1,6-bisphosphate

10.0 mM

AMP

0.10 mM

ADP

0.50 mM

ATP

5.0 mM

Pi

10.0 mM

 

 

 

2)                  In your secret room in the back of the house, you make wine that is 10% w/v EtOH.  What molar concentration of glucose (or equivalent) would be required for this to occur, given the fermentation reaction of yeast to recover NADH from pyruvate?  The molecular weight of ethanol is about 46 g/mol.

 

 

 

3)                  Which carbons of glucose, catabolized through glycolysis and the Krebs cycle, will be lost most rapidly as CO2?

 

 

 

4)                  Calculate DGo' for the oxidation of malate by malate dehydrogenase in the Krebs’ Cycle:

Malate + NAD+ ¾ Oxaloacetate + NADH + H+

                        Standard reduction potentials for the half-reactions are below.

 

Oxaloacetate + 2e- + 2H+

Malate

-0.17 V

NAD+ + 2e- + 2 H+

NADH + H+

-0.32 V

 

 

5)                  What would DGo' be for an enzyme that oxidizes succinate with NAD+ instead of FAD?  If  [succinate]/[fumarate] = 10, what is the minimum [NAD+]/[NADH] ratio to make the reaction exergonic?

Fumarate + 2e- + 2H+

Succinate

+0.03 V

NAD+ + 2e- + 2 H+

NADH + H+

-0.32 V

 

 

6)                  For the reaction:

GSSG + NADPH + H+

2GSH + NADP+

 

 

GSSG + 2e- + 2H+

2GSH

-0.23 V

NADP+ + 2e- + 2 H+

NADPH + H+

+0.32 V

 

a)      Calculate DGo

 

b)      What would be the effect on DGo’ of using NADH instead of NADPH?

 

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