Question

9. State briefly, us ing appropriate equations and enzymes, what would happen to Glucose-6-phosphate in a rapidly dividing cell where more ribose-5-phosphate than NADPH is required. (10 pts)

Answer 1

Fructose - 6 - phosphate and glyceraldehyde - 3 - phosphate are diverted from glycolysis and converted to ribose -5- phosphate. Oxidative phase is primarily used, 2 molecules of NADPH are made from 1 ribose -5- phosphate, it requires 1 molecule of glucose - 6 - phosphate.

4 steps of pentose phosphate pathway are 1. much more ribose 5 phosphate than NADPH is required. rapidly dividing cells require ribose 5 phosphate for the synthesis of DNA nucleotide precursors. Most of the glucose 6 phosphate is converted into fructose 6 phosphate and glyceraldehyde 3 phosphate by the glycolytic pathway. Transaldolase and transketolaseconvert two molecules of fructose 6 phosphate and one molecule of glyceraldehyde into three molecules of ribose 5 phosphate by the reversal of reactions.

5Glucose 6 phosphate + ATP (gives rise to) 6ribose 5 phosphate + ADP + H+

2. Need for NADPH and ribose 5 phosphate are balanced.

Glucose 6 phosphate + 2NADP+ + H2O (gives rise to)   ribose 5 phosphate + 2NADPH + 2H+ + CO2   

3. Much more NADPH than ribose 5 phosphate is required.

Glucose 6 phosphate  + 12NADP+ + 7H2O (gives rise to) 6CO2 + 12NADPH + 12H+ Pi

4. Both NADPH and ATP are required.

3Glucose 6 phosphate + 6NADP+ + 5NAD+ + 5Pi + 8ADP (gives rise to) 5Pyruvate + 3CO2 + 6NADPH + 5NADH + 8ATP + 2H2O + 8H+