The Reducing Power of the Cell Flashcards
What is NADPH and why is it important?
NADPH comes from NADP which has been reduced. It is essential in anabolic pathways, involved in fatty acid synthesis, and protects against oxidative damage.
What is oxidative damage?
When red blood cells are exposed to high oxygen levels, they may form reactive oxygen species.
Glutathione is said to need NADPH. Why?
NADPH serves as an antioxidant. It is also a coenzyme of glutathione reductase which replenishes glutathione levels
What is coupled with the reduction of NADP to NADPH?
Oxidation of GSH to GSSG
When NADPH levels are low, the cell…
would flux the pentose phosphate pathway to replenish NADPH levels
What is the pentose phosphate pathway and what are its stages?
It replenishes NADPH levels and has 3 main stages:
1. oxidative stage
2. non-oxidative stage
3. recycling of carbon
Pentose Phosphate Pathway
In step 1 of stage 1 (oxidative stage), what type of reaction, enzyme, substrates, and products are involved?
A dehydration reaction, catalyzed by G6P dehydrogenase, G6P + 2NAD+ + H2O is converted to ribose-5-phosphate + CO2 + 2 NADPH + 2H+
Pentose Phosphate Pathway
In step 2 of stage 1 (oxidative stage), what type of reaction, enzyme, substrates, and products are involved?
ring opening, catalyzed by 6-phosphogluconolactonase, converts 6-phosphoglucono-δ-lactone from G6P to 6-phosphogluconic acid
Pentose Phosphate Pathway
In step 3 of stage 1 (oxidative stage), what type of reaction, enzyme, substrates, and products are involved?
Dehydration reaction, catalyzed by 6-phosphogluconate dehydrogenase, converts 6-phosphogluconate to ribulose-5-phosphate
Pentose Phosphate Pathway
In the second stage, it is known as a non-oxidative stage. What is/are enzyme/s, substrates, and products involved?
ribulose-5-phosphate (Ru5P) catalyzed by ribulose-5P-isomerase produces xylulose-5-phosphate (xylulose-5P)
Pentose Phosphate Pathway
In the third stage, it is known as a recycling of carbon molecules stage. Can you explain the mechanism behind it?
- xylulose-5-phosphate + ribose-5-phosphate is converted to G3P and sedoheptulose-7-phosphate catalyzed by transketolase in the presence of TPP.
- G3P + sedoheptulose-7-phosphate is converted to Erythrose-4-phosphate and Fructose-6-phosphate catalyzed by transaldolase.
- xylulose-5-phosphate + erythrose-4-phosphate is converted to G3P and Fructose-6-phosphate catalyzed by transketolase in the presence of TPP.
Pentose Phosphate Pathway
Why does the third stage require the use of 2 enzymes, one of which is used twice?
To make sure efficiency in the production of G3P and F6P which can enter glycolysis.
