Pentose Phosphate Pathways????

[NRAI2001]

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I m reading the metabolic chp of Berkeley review (section 8) right now, and I m trying to learn what the pentose phosphate pathway is. I don't really see what TBR is getting at. If you have the berkeley review books its on page 207 in the second bio book.

Can someone please explain to me what the pentose phosphate pathway is? What is its purpose? Where does it occur?

So far what I have gotten out of the reading (don't know if this correct or not) is that its used to create NADPH, which is used in anabolic processes bc of its reducing nature, where NAD is used in catabolic processes bc of its oxidizing nature????? If this is true, how is NADPH different from NADH?

Thanks, if u can answer this question, ur set on the bio sections 🙂

 

[dtreese]

I can, but it'll take a while to type. Check back in a few minutes.

 

[dtreese]

Okay, first of all, this is waaaaay more than you need for the MCAT, but caramels to you for caring!

There are two main things we get from the pentose phosphate pathway (also called the hexose monophosphate shunt or the 6-phosphogluconate pathway, just to torment us). For one, the pathway, WITHOUT USING ATP, interconverts 3, 4, 5, 6 and 7-carbon sugars. One of these is ribose 5-phosphate, essential for DNA and RNA synthesis. The other major product of the pentose phosphate pathway is NADPH.

You asked what the difference is between NAD and NADP. The short answer is "a phosphate group." The more helpful answer is that the phosphate group affects the steady-state equilibrium concentrations. The ss ratio of NADP+/NADPH is about .1, which means that NADPH is a good electron donor (i.e. a good reducing agent). The ratio of NAD+/NADH, on the other hand, is about 1000 in the liver, which makes NAD+ an excellent electron acceptor (i.e. an excellent oxidizing agent).

NADPH is used in a variety of reactions. It is used in the synthesis of fatty acids and steroids, and it is also used to regenerate glutathione, an important neutralizer of free radicals. Glutathione neutralizes free radicals by dimerizing. Two glutathione molecules form a disulfide bridge, donating the H's from the SH's on their cysteine residues, in order to neutralize free radicals. The glutathione is then reduced (thus regenerated) by NADPH. NADPH participates in the cytochrome p450 monooxygenase system, which in mitochondria hydroxylates steroids and in liver smooth ER detoxifies foreign substances through hydroxylation.

After blathering all that out, I checked my biochem book, and it's kind of scary that I remembered it so well. I even remembered where they used the term "xenobiotics." *shudder*

 

[NRAI2001]

Okay, first of all, this is waaaaay more than you need for the MCAT, but caramels to you for caring!

There are two main things we get from the pentose phosphate pathway (also called the hexose monophosphate shunt or the 6-phosphogluconate pathway, just to torment us). For one, the pathway, WITHOUT USING ATP, interconverts 3, 4, 5, 6 and 7-carbon sugars. One of these is ribose 5-phosphate, essential for DNA and RNA synthesis. The other major product of the pentose phosphate pathway is NADPH.

You asked what the difference is between NAD and NADP. The short answer is "a phosphate group." The more helpful answer is that the phosphate group affects the steady-state equilibrium concentrations. The ss ratio of NADP+/NADPH is about .1, which means that NADPH is a good electron donor (i.e. a good reducing agent). The ratio of NAD+/NADH, on the other hand, is about 1000 in the liver, which makes NAD+ an excellent electron acceptor (i.e. an excellent oxidizing agent).

NADPH is used in a variety of reactions. It is used in the synthesis of fatty acids and steroids, and it is also used to regenerate glutathione, an important neutralizer of free radicals. Glutathione neutralizes free radicals by dimerizing. Two glutathione molecules form a disulfide bridge, donating the H's from the SH's on their cysteine residues, in order to neutralize free radicals. The glutathione is then reduced (thus regenerated) by NADPH. NADPH participates in the cytochrome p450 monooxygenase system, which in mitochondria hydroxylates steroids and in liver smooth ER detoxifies foreign substances through hydroxylation.

After blathering all that out, I checked my biochem book, and it's kind of scary that I remembered it so well. I even remembered where they used the term "xenobiotics." *shudder*

Thanks for the long reply. 🙂