Consider a cell that requires much more ribose5-phosphate than NADPH. The cell needs ribose 5-phosphate but has a relatively high concentration of NADPH and a low concentration of NADP+. These conditions may occur in rapidly dividing cells. What is the fate of glucose 6-phosphate, glycolytic intermediates, and pentose phosphate pathway intermediates in this cell? Most of the glucose 6-phosphate enters the pentose phosphate pathway. One molecule of glyceraldehyde 3-phosphate and two molecules of fructose 6-phosphate are used to generate three molecules of ribose 5-phosphate. Most of the glucose 6-phosphate enters the glycolytic pathway and is converted to fructose 6-phosphate and glyceraldehyde 3-phosphate. Glycolytic intermediates can only enter the pentose phosphate pathway through conversion to pyruvate and subsequent gluconeogenesis. Under the given conditions, all triose phosphates are converted to pyruvate by the glycolytic pathway. The oxidative pentose phosphate pathway reaction catalyzed by glucose 6-phosphate dehydrogenase is slowed down.

Consider a cell that requires much more ribose5-phosphate than NADPH. The cell needs ribose 5-phosphate but has a relatively high concentration of NADPH and a low concentration of NADP+. These conditions may occur in rapidly dividing cells. What is the fate of glucose 6-phosphate, glycolytic intermediates, and pentose phosphate pathway intermediates in this cell? Most of the glucose 6-phosphate enters the pentose phosphate pathway. One molecule of glyceraldehyde 3-phosphate and two molecules of fructose 6-phosphate are used to generate three molecules of ribose 5-phosphate. Most of the glucose 6-phosphate enters the glycolytic pathway and is converted to fructose 6-phosphate and glyceraldehyde 3-phosphate. Glycolytic intermediates can only enter the pentose phosphate pathway through conversion to pyruvate and subsequent gluconeogenesis. Under the given conditions, all triose phosphates are converted to pyruvate by the glycolytic pathway. The oxidative pentose phosphate pathway reaction catalyzed by glucose 6-phosphate dehydrogenase is slowed down.

Biochemistry

9th Edition

ISBN:9781319114671

Author:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.

Publisher:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.

Chapter1: Biochemistry: An Evolving Science

Section: Chapter Questions

Problem 1P

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When the cells of our body are in dire need to synthesize Ribose 5 phosphate and it has already enough supply of NADPH, reverse non oxidative pathway of the HMP shunt pathway takes place. If the cell has 10 glucose 6 phosphate molecules, how many of these would be converted to Fructose 6 phosphate and how many to form glyceraldehyde 3 phosphate respectively to synthesize maximum number of Ribose 5 phosphate? 8:2 2:8 4:6 6:4
Some anaerobic bacteria use alternative pathways for glucose catabolism that convert glucose to acetate rather than to pyruvate. Shown below is one possible metabolic pathway. The first part of this pathway (glucose to fructose-1,6-bisphosphate) is identical to the glycolytic pathway. In the second part of the alternative pathway, Enzymes 1–6 all have mechanisms/ activities analogous t enzymes in glycolysis. Note that there are two C¬C bond cleavage reactions in this new pathway: A → B + C (Enzyme 1) and C → B + D. All the steps where ATP is consumed or generated have been shown; however, the addition or loss of NAD+/NADH, Pi , H2O, or H+ has not been shown explicitly. Draw the structures for the intermediates B, F, G, H, and I, and include other reaction participants as needed.
Complete the sentence describing the pentose phosphate pathway in cells that require much more ribose 5-phosphate than NADPH. These cells need ribose 5-phosphate but have relatively higher concentrations of NADPH and lower concentrations of NADP*. Choose from the listed words to fill in the blanks: xylulose 5-phosphate, fructose 6-phosphate, glucose 6-phosphate, five, two, three, glyceraldehyde 3- phosphate, erythrose 4-phosphate, sedoheptulose 7-phosphate. One molecule of and two molecules of are used to generate molecules of ribose 5-phosphate by the reverse reactions of the nonoxidative phase of the pentose phosphate pathway.
Glucose is phosphorylated to glucose-6-phosphate by hexokinase in the first step of the glycolytic pathway to trap it in the cell, as G6P cannot diffuse across the lipid bilayer. This reaction also decreases the concentration of free glucose, favoring additional import of the molecule. However, this has a postive standard free energy of 3 kcal per mole. To favor this reaction, hydrolysis of ATP is coupled, which has a standard free energy of -7 kcal per mole. Determine the actual free energy change in kcal/mole for the following conditions: Glucose concentration: 4.5 mM ATP conc: 3.79 mM G6P conc. 0.052 mM ADP conc: 0.12 mM inorganic phosphate conc: 1.3 mM temperature: 313 K Ans. in 3 SFs.
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