Wood, T. The Pentose Phosphate Pathway, Zimmer, H. Pentose Phosphate Pathway. Encyclopedia of Life Sciences. Our medical articles are the result of the hard work of our editorial board and our professional authors.
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Votes: 14, average: 4. About the Lecturio Medical Online Library Our medical articles are the result of the hard work of our editorial board and our professional authors. So, that's kind of usually the end product we think of when we think about breaking down glucose.
But, the pentose phosphate pathway is kind of a unique pathway, because it turns out that in this pathway no ATP is consumed or produced. That's kind of unique, to point out. So, where does it fit in to this overall pathway? It turns out that the linear way I've written cellular respiration is actually only partly true. It's a great way to conceptualize it, but there are many branches or kind of side reactions that are taking place almost simultaneously with the breakdown of glucose, and the pentose phosphate pathway is one of these.
So, turns out that as glucose begins to go through glycolysis, some of it is shunted away to become the pentose phosphate pathway. So, glucose continues to be broken down, but it continues to be broken down to produce different products than it would if it continued through going through glycolysis, and Krebs, and then to the electron transport chain.
So, as you can see, I've written pentose phosphate pathway kind of suggestively by highlighting pentose and phosphate in different colors to point out to you that there are two primary products in this pathway.
So, the first is the production of a five-carbon pentose sugar. So, pentose is just another word for five-carbon sugar, and the particular name of this sugar is ribose-five-phosphate. And this sugar, so it's a five-carbon sugar, I'll go ahead and draw that to remind us of that, is an important substrate in producing DNA and RNA.
So, if you remember, DNA and RNA contain nucleotides, and the nucleotides contain a nitrogenous base, a phosphate group, and a five-carbon sugar.
But, in either case, this ribose-five-phosphate is an important precursor to creating DNA and RNA, so, quite a crucial molecule. Now, the second primary product of this reaction, as this phosphate nicely implies, is a phosphorylated molecule that is usually abbreviated as N-A-D-P, P standing of course for the phosphate in this molecule, H.
So, this is not to be confused with the NADH, which, if you recall, I'll go ahead and actually draw that in here, if you recall, NADH is actually produced in cellular respiration during the breakdown of glucose.
So, this produces NADH, which, of course, contributes electrons to the electron transport chain. So, of course, the question you might have in your mind is how is NADH different from the easily confused NADPH, because they sound like similar molecules, and in many ways they are.
So, of course, the H forms of these molecules are the reduced form of these molecules, and the plus, or oxidized form of these molecules, are the NAD-plus and NADP-plus.
But, what's different about these two pairs of molecules is the relative amount of the reduced form and the oxidized form inside the cell. Ribulosephosphate can alternatively undergo a series of isomerizations as well as transaldolations and transketolations that result in the production of other pentose phosphates including fructosephosphate, erythrosephosphate, and glyceraldehydephosphate both intermediates in glycolysis. These compounds are used in a variety of different biological processes including production of nucleotides and nucleic acids ribosephosphate , as well as synthesis of aromatic amino acids erythrosephosphate.
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