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On the 5th step in glycolysis, triose-phosphate isomerase converts dihydroxy-acetone-phosphate to glyceraldehyde-3-phosphate. Now my question is: Why?

Most books and sites I've read only say that glyceraldehyde-3-phosphate has a direct pathway compared to dihydroxy-acetone-phosphate. Anyone with additional info on this would help much if they shared.

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    $\begingroup$ Can you please clarify your question? Actually I am not sure, if I understand what you are asking. $\endgroup$
    – Chris ♦
    Nov 14 '18 at 6:52
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    $\begingroup$ Welcome to SE Biology. Unfortunately your question is unclear and does not yet meet our standards. It could be made to do so if you edit it. First, as a new poster, you should take the Tour and read the Help on Asking Good Questions. You should also look at other questions on the site where you will see that we use standard English here, not textese. Most important, we cannot explain statements you encounter in your reading unless you quote word for word and name the source (with a link if possible). $\endgroup$
    – David
    Nov 14 '18 at 8:39
  • $\begingroup$ Thank you .I'm new, I will read through the guidelines and try to rephrase the question. $\endgroup$
    – Derrick. K
    Nov 14 '18 at 14:37
  • $\begingroup$ "a direct pathway" to what? If you consult a text to complete that phrase you will most likely see the answer to your question yourself. In any case wiithout completing it your question is still unclear, regardless of any scatter-gun answers that are posted. $\endgroup$
    – David
    Nov 14 '18 at 17:46
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"Why" questions in biology tend not to make sense- https://en.wikipedia.org/wiki/Teleology_in_biology

But perhaps if I narrate the reaction it will connect with your intuition. Let's look at the reactions in question:

Glycolysis Summary https://en.wikipedia.org/wiki/Glycolysis#Summary_of_reactions

Step 4 in glycolysis cleaves fructose 1,6-bisphosphate into two molecules that are isomers. One isomer (glyceraldehyde 3-phosphate, GADP) is a reactant in step 6, and fuels the “payout phase” where glycolysis reactions begin to yeild ATP and NADH. So what happens to dihydroxyacetone phosphate (DHAP), the other product from step 4? How can we extract energy from this?

Reaction 5 is the interconversion of GADP and DHAP. So as GADP is consumed by reaction 6, reaction 5 will, by Le Chatlier’s principle, lead to net conversion of DHAP to GADP. The GADP produced by this isomerization then also feeds reaction 6. In this way, both of the products of reaction 4, GADP and DHAP, are channeled down the chain to fuel NADH and ATP production.

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