I couldn't find this question directly asked so I thought I would ask it

In Fundamentals of Biochemistry 3e (Voet et al), it has a small small little comment about pyrimidine synthesis: (In a diagram showing UMP synthesis) "In the eukaryotic enzyme, which contains FMN and nonheme Fe, is located on the outer surface of the inner mitochondrial membrane where quinones supply its oxidizing power. The other five enzymes of pyrimidine biosynthesis are cytosolic in animal cells."

So it seems for the most part pyrimidine synthesis occurs in the cytosol??

When the book talks about purine synthesis no mention is made of where this is actually happening in the cell.

Also, if nucleotides are being made in the cytosol, I suspect there must be some kind of membrane protein that allows nucleotides to cross the nuclear and mitochondrial membranes... what are they??

I'm a visual person, and knowing where and how these things are happening in the cell helps me understand it better than just following what's happening after each synthesis step.



1 Answer 1


Correct, all but one step in pyrimidine synthesis occurs in the cytosol, and purine synthesis occurs in the cytosol only.

Nucleotides freely diffuse through nuclear pores but are actively transported through mitochondrial membranes via embedded membrane transport proteins (i.e. ATP-ADP translocators, GTP transporters, and pyrimidine nucleotide transporters).


  • 1
    $\begingroup$ I should add that nucleotides can also pass through nuclear and mitochondrial membranes as cofactors for some proteins. $\endgroup$
    – boloyao
    Jul 21, 2014 at 2:46

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