AAMC outline: Oxidative Phosphorylation - NADPH?

[FOCUSandEARNit]

Hey MCAT team,

under section 1D of the AAMC outline, it lists the following...

Oxidative Phosphorylation...
-Electron transfer in mitochondria

• NADH, NADPH
• Flavoproteins
• Cytochromes

NADH, flavoproteins and cytochromes - sure. but NADPH? why is that in here? NADPH is relevant to the pentose phosphate pathway and in the biosynthesis of fatty acids....but ETC?

what are your thoughts?

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[goodtime]

NADPH is strictly an anabolic coenzyme i guess they mean just know its a carrier of electrons or they just screwed up

 

[RH8448]

I've been trying to find an answer for you though. NADPH is an electron carrier. It does the things you mention. One thing to note about NADPH is that it is involved in restoring the reducing power of other proteins/enzymes. For example, glutathione needs reducing power and it gets that from NADPH. If we didn't have NADPH the mitochondrial membrane would degrade due to oxidative stress. I've also read that some NADPH is made in the mitochondria but that sounds a little too specific for the MCAT. As far as the outline goes, I wouldn't say it is an error.

 

[FOCUSandEARNit]

NADPH reduces the acetyl groups added to the fatty acid in fatty acid synthase...but that occurs in the cytosol, and just outside the mitochondria.

Kaplan and Khan dont mention it. I'm just going to make sure I know what NADPH is used for (and when and where) and know the structural differences in NADH / NADPH.

 

[tturchi51]

Well this is news to me I thought NADPH was the NADH of the dark rxs in photosynthesis.

After reading about it I think they want us to know the ratio and why its significant.

"Inside the cell the ratio of NAD+ to NADH is kept high, whereas the ratio of NADP+ to NADPH is kept low. "

"This provides plenty of NAD+ to act as an oxidizing agent and plenty of NADPH to act as a reducing agent—as required for their special roles in catabolism and anabolism, respectively."

Something like if NADP+ to NADPH ratio was high what would happen to ox phorphorylation? or the NAD+?

 

[FOCUSandEARNit]

ok khan academy video on pentose phosphate pathway: https://www.khanacademy.org/test-pr...ydrate-metabolism/v/pentose-phosphate-pathway

this is basically what she says around the 4 min mark.

NAD+/NADH ratio in cell 1000:1 —> much much higher NAD+; most NAD+ wants to accept electrons in breakdown of glucose, wants to accept electrons for krebs cycle reactions

NADP+/NADPH ratio in cell 1:10 —> much higher NADPH; NADPH wants to donate electrons

• very important in anabolic reactions (build up of molecules) - reducing power for these reactions (e.g. fatty acid synthesis, pentose phosphate pathway)
• maintains store of antioxidants in the body! NADPH reduces reactive oxygen species --> this is directly relatable to ETC because of ETC's role in apoptosis and oxidative stress

sooooo what do we think?

 

[tturchi51]

NAD+/NADH ratio in cell 1000:1 —> higher NAD+ ratio most NAD+ wants to accept electrons (reduction/oxidizing agent) for e- in krebs cycle and other catabolic rxs

NADP+/NADPH ratio in cell 1:10 —> much higher NADPH ratio; NADPH wants to donate electrons (oxidation/reducing agent) in anabolic rxs

NAPH-maintains store of antioxidants in the body! NADPH reduces reactive oxygen species --> this is directly relatable to ETC because of ETC's role in apoptosis and oxidative stress

I combined what we said and will now copy+paste (merge format) to my biochem notes!