The oxygen anion in the phosphate group is likely to be bonded with a hydrogen cation and thus forming a hydroxyl.

When the phosphate group is condensed with glycerol to make a phospholipid, is the hydroxyl from the glycerol molecule taken or the hydroxyl from the phosphate group taken?

I believe it's related to the difference of electronegativity of oxygen and phosphorus which causes unequal sharing of electrons between atoms, thus making a hydroxyl from one side easier to get taken off than the hydroxyl from the other side is.

  • $\begingroup$ I'm trying to figure out where in the process you are talking about. Are you asking about the creation of Glucose 6-phosphate, phosphatidic acid, or phospholipids down stream of DAG? I was originally thinking the creation of phosphatidic acid, but I'm not sure. $\endgroup$ – Atl LED Oct 18 '13 at 13:05

In all phosphorylation reactions, the oxygen of the hydroxyl group in the substrate attacks P of phosphate. This is because of high partial positive charge on P which is bonded to four highly electronegative oxygen atoms. When the bond forms between the substrate oxygen atom and phosphorus of terminal phosphate, electrons are transferred to the O that bridges the ester bond between 2nd and 3rd phosphate. Therefore the O of the substrate is retained and that of the terminal phosphate (of ATP) becomes the part of the 2nd phosphate (now terminal phosphate of ADP).

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My recollection is that the formation of a phospholipid normally involves acylation of glycerol 3-phosphate. Glycerol 3-phosphate is a glycolytic intermediate, and so there is no actual phosphorylation of a glycerol; the phosphate on the glycerol will have come from the phosphorylation of glucose or of fructose 6-phosphate.

In a kinase reaction the oxygen of the -OH in the acceptor acts as a nucleophile at the P of the phosphate, so in terms of your question the O atom comes from the acceptor, not the donor. Presumably if there was a glycerol kinase (I expect there is) it would have the same mechanism so the O would come from the glycerol.


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