Pentose

Question 1

Discuss the oxidative stage of the pentose phosphate pathway

Answer 1

We begin with our good friend glucose-6-phosphate. Using Glucose-6-phosphate dehydrogenase, we turn it into 6-phosphogluconolactone and NADP+ to NADPH.

To shorten it, we use gluconolactonase to turn this big guy into 6-phosphogluconate.

The final set of reactions uses 6-phosphogluconate dehydrogenase to turn it into ribulose-5-phosphate, CO2 and another NADPH

Question 2

Deficiency of glucose-6-phosphate dehydrogenase

Answer 2

This means we have a lot less NADPH floating around. Because of this, glutathione can not be reduced (needed to reduce H2O2), so we can’t restore its redox capabilities. RBCs start to lyse and we get a hemolytic anemia.

While being protected against malaria, these x-linked individuals are in trouble.

Question 3

Discuss the non-oxidative phase of the pentose phosphate pathway

Answer 3

Ribulose 5 phosphate that we made at the end of the oxidative phase is isomerized to begin this new set of reactions to ribose 5 phosphate, or is epimerized to xylulose 5-phosphate.

These two compounds both undergo reactions via transketolase and transaldolase that transfer carbons, ultimately forming fructose 6-phosphate and glyceraldehyde 3-phosphate

Transketolase requires thiamine pyrophosphate and transfers two carbons. Transaldolase cause its Awesome does not require anything and can transfer 3 carbon units.

Question 4

Discuss the overall numbers of reactants and products for the pentose phosphate pathway

Answer 4

Xylulose is formed 2x as often as ribose 5p.

3Glucose-6-p and 6NADP+ generate 3 ribulose 5-p and 6NADPH in the oxidative stages.

In the non oxidative stages, the 3 Ribulose 5-ps get turned into 2 xyluloses and 1 ribose 5-Ps. These then get turned to 2 Fructose 6-Ps and 1 glyceraldehyde-3-P

Question 5

Purpose of the Pentose Phosphate pathway?

Answer 5

The products glyceraldehyde and fructose-6-p enter glycolysis, but the main purpose of this system is to make NADPH for fatty acid synthesis.

Question 6

What happens in the Pentose pathway when NADPH levels are high? Low?

Answer 6

Low NADPH levels means the oxidative reactions of the pathway can be used to make more NADPH, thus causing a generation of Ribose-5-Phosphate for nucelotide synthesis.

High NADPH means we need to go backwards, but we cannot go backwards on the oxidative portion. We instead go back from the nonoxidative portion to generate ribose-5-P from fructose-6-phosphate and glyceraldehyde-3-phosphate, again leading to nucleotide synthesis.