Pentose-Phosphate pathway Flashcards
What is the ratio of NADH to NAD+ in cells?
Why?
1/1000 (NADH/NAD+)
The reason is that NADH generated by glycolysis and CAC is efficiently used up by the mitochondria in the ETC.
Why can’t NADH be used as a reducing power?
It is very low in concentration in the cell because it is efficiently used up by the mitochondria.
What is used instead of NADH for its reducing power? Why can it be used?
NADPH.
Cannot be used in oxidative phosphorylation, mitochondria cannot used it.
NADPH is 100x more abundant than NADP+ and thus can carry out synthetic reactions.
The second reason is that NADPH is used to quench oxygen radicals.
What are the two reasons for the use of NADPH?
1 - Reducing power for synthetic reactions
2 - Reducing power to neutralize oxygen radicals.
When would we require a lot of NADPH?
During cell division, to generate ribose sugar for nucleic acids.
During periods of oxidative stress.
What is the overall reaction of the pentose-phosphate pathway?
3 G6P + 6 NADP+ + 3 H2O –> 6 NADPH + 6H+ + 3 CO2 + 2 F6P + GAP
How many enzymes are involved in the pentose-phosphate pathway?
7
What are the different, major steps of the pentose-phosphate pathway?
1 - Oxidation reactions
2 - Isomerization and epimerization reactions
3 - C-C bond cleavage and formation reactions
What are the different enzymes that fall under the oxidative reactions?
G6PDH
6-phosphogluconolactonase
6-phosphogluconate DH
What are the enzymes that fall under the isomerization and epimerization reactions?
Ribulose-5-phosphate isomerase
Ribulose-5-phosphate epimerase
What are the enzymes that fall under the C-C bond cleavage and formation reactions?
Transketolase
Transaldolase
The pentose-phosphate pathway starts with G6P, why not glucose?
Glucose is immediately phosphorylated by HK.
Per molecule of G6P, how much NADPH is produced?
2 NADPH
Out of 3 glucose molecules, how many CO2 come out? How many F6P and GAP?
3 CO2
2 F6P
1 GAP
What is the side product of the pentose-phosphate pathway?
R5P
What is the main enzyme that controls the flux of this pathway?
How is it regulated?
G6PDH
Strongly inhibited by NADPH
As the concentration of NADPH goes up, the activity of this enzyme decreases.
In the pentose-phosphate pathway, there is a very important side product. What is it and why is it not an end product?
R5P, used for generation of nucleic acids.
Not an end product since it gets recycled back to glucose or is used up.
______ is used to generated reduced _______.
NADPH
Glutathione (GSH)
_____ plays a critical role in quenching the oxyradicals in the cells.
GSH
If ______ generation is inhibited due to a mutation in ___DH, cells become susceptible to oxidative damage.
NADPH
G6P
People with a ______ defect are resistant to malaria.
G6PDH
What occurs if oxygen is not given two electrons to become H2O?
Becomes superoxide, negatively charged, unpaired electron
What enzyme deals with superoxides?
Superoxide dismutase
What does superoxide dismutase do?
Converts superoxides to hydrogen peroxide
How is hydrogen peroxide converted to water?
Glutathione peroxidase
How does glutathione peroxidase neutralize hydrogen peroxide?
Reduced form of glutathione peroxidase gives a hydrogen to make 2 H20 and becomes oxidized.
How goes oxidized glutathione peroxidase get reduced again?
Glutathione reductase, using NADPH, reduces oxidized glutathione peroxidase.
What occurs if hydrogen peroxide accumulates?
Takes one proton/electron and gets converted to water and OH radical
How are people with a defective version of G6PDH resistant to malaria?
Increased oxidative stress in the blood system causes invading parasite, which is very susceptible to oxygen radicals, to die.
