The Reducing Power of the Cell

Question 1

What is NADPH and why is it important?

Answer 1

NADPH comes from NADP which has been reduced. It is essential in anabolic pathways, involved in fatty acid synthesis, and protects against oxidative damage.

Question 2

What is oxidative damage?

Answer 2

When red blood cells are exposed to high oxygen levels, they may form reactive oxygen species.

Question 3

Glutathione is said to need NADPH. Why?

Answer 3

NADPH serves as an antioxidant. It is also a coenzyme of glutathione reductase which replenishes glutathione levels

Question 4

What is coupled with the reduction of NADP to NADPH?

Answer 4

Oxidation of GSH to GSSG

Question 5

When NADPH levels are low, the cell…

Answer 5

would flux the pentose phosphate pathway to replenish NADPH levels

Question 6

What is the pentose phosphate pathway and what are its stages?

Answer 6

It replenishes NADPH levels and has 3 main stages:
1. oxidative stage
2. non-oxidative stage
3. recycling of carbon

Question 7

Pentose Phosphate Pathway

In step 1 of stage 1 (oxidative stage), what type of reaction, enzyme, substrates, and products are involved?

Answer 7

A dehydration reaction, catalyzed by G6P dehydrogenase, G6P + 2NAD+ + H2O is converted to ribose-5-phosphate + CO2 + 2 NADPH + 2H+

Question 8

Pentose Phosphate Pathway

In step 2 of stage 1 (oxidative stage), what type of reaction, enzyme, substrates, and products are involved?

Answer 8

ring opening, catalyzed by 6-phosphogluconolactonase, converts 6-phosphoglucono-δ-lactone from G6P to 6-phosphogluconic acid

Question 9

Pentose Phosphate Pathway

In step 3 of stage 1 (oxidative stage), what type of reaction, enzyme, substrates, and products are involved?

Answer 9

Dehydration reaction, catalyzed by 6-phosphogluconate dehydrogenase, converts 6-phosphogluconate to ribulose-5-phosphate

Question 10

Pentose Phosphate Pathway

In the second stage, it is known as a non-oxidative stage. What is/are enzyme/s, substrates, and products involved?

Answer 10

ribulose-5-phosphate (Ru5P) catalyzed by ribulose-5P-isomerase produces xylulose-5-phosphate (xylulose-5P)

Question 11

Pentose Phosphate Pathway

In the third stage, it is known as a recycling of carbon molecules stage. Can you explain the mechanism behind it?

Answer 11

1. xylulose-5-phosphate + ribose-5-phosphate is converted to G3P and sedoheptulose-7-phosphate catalyzed by transketolase in the presence of TPP.
2. G3P + sedoheptulose-7-phosphate is converted to Erythrose-4-phosphate and Fructose-6-phosphate catalyzed by transaldolase.
3. xylulose-5-phosphate + erythrose-4-phosphate is converted to G3P and Fructose-6-phosphate catalyzed by transketolase in the presence of TPP.

Question 12

Pentose Phosphate Pathway

Why does the third stage require the use of 2 enzymes, one of which is used twice?

Answer 12

To make sure efficiency in the production of G3P and F6P which can enter glycolysis.