Question: Which of the following conversions take place in a metabolic situation

Question

Question: Which of the following conversions take place in a metabolic situation that require much more NADPH than ribose 5-phosphate, as well as complete oxidation of glucose 6-phosphate to CO2? [The arrows represent one or more enzymatic steps]

a.   Glucose 6-phosphate   —> —>    ribulose 5-phosphate

b.    Fructose 6-phosphate + glyceraldehydes 3-phosphate —>   —>    ribose 5-phosphate

c.   Ribose 5-phosphate   —> —>      fructose 6-phosphate + glyceraldehydes 3-phosphate                                  

d.   Glyceraldehydes 3-phosphate   —> —>      pyruvate

e.    Fructose 6-phosphate   —> —>    glucose 6-phosphate

Explanation / Answer

Answer

c.   Ribose 5-phosphate   —> —>      fructose 6-phosphate + glyceraldehydes 3-phosphate

Rapidly dividing cells need ribose 5-phosphate for the synthesis of nucleotide.

6Glucose 6 phosphate + 12NADP+ + 6H2O --- 6 Ribose 5 Phosphate + 12NADPH + 12H+ + 6CO2

Ribose 5-phosphate is converted into fructose 6-phosphate and glyceraldehyde 3-phosphate by transketolase and transaldolase.
6 Ribose 5 phosphate ----- 4 fructose 6 phosphate + 2 Glyceraldehyde 3 phosphate.

Then,
4 fructose 6 phosphate + 2 Glyceraldehyde 3 phosphate + H2O --- 5 Glucose 6 phosphate + pi.

The overall reaction becomes
Glucose 6 phosphate + 12NADP+ + 7H2O --- 6CO2 + 12NADPH + 12H+ + pi

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