Why does FA say only odd-chain fatty acids can enter TCA cycle?

[Old Style Nanny]

Can't even chain FAs enter the cycle as Acetyl CoA?

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[Wolverines83]

Can't even chain FAs enter the cycle as Acetyl CoA?

b-oxidation is done two carbons at a time. the reason odd-chains enter tca is b/c there is one carbon left at the end that can't be oxidized...so rather than waste it, into tca it goes

edit: to answer your question, the acetyle coa that results from each step of B ox does enter. They're just saying odd chains can't be finished off by b-ox and that they need to be converted to aCoa

 

[Old Style Nanny]

edit: to answer your question, the acetyle coa that results from each step of B ox does enter. They're just saying odd chains can't be finished off by b-ox and that they need to be converted to aCoa

Oh okay, got it. Would it kill them to word it clearer? Thanks.

 

[nikmad]

Actually it is mentioned so because in the tca cycle, acetyl coa is thrown out as two molecules of carbon dioxide before it reaches the oxaloacetate stage, so there is no net gain of carbon. Oxalo acetate is what we need more of to make glucose. and other molecules contribute to gluconeogenesis by becoming oxaloacetate via puruvate(eg: alanine, lactate)
these two pic should clear things right up http://student.ccbcmd.edu/~gkaiser/biotutorials/cellresp/images/u4fg35.jpg
http://chemistry.gravitywaves.com/CHE452/images/FatesPyruv.gif (notice the arrows on this one, reversible vs irreversible)
Cheers.

 

[Phloston]

Isoleucine and valine (as branched-chain aa's) enter the TCA beginning from propionyl-CoA (same as odd-chain FAs); leucine enters as acetyl-CoA.

Propionyl-CoA carboxylase and pyruvate carboxylase both convert 3Cs --> 4Cs.

Acetyl-CoA carboxylase is 2Cs --> 3Cs.