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
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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