Pentose Phosphate Pathway and Lipid Metabolism

Respiration Review

As you may recall respiration can be summarized simply by the following:

CH₂O + O₂ → CO₂ + H₂O + energy

Also just as in animals, this process is far more complex that that simple formula. There are four sections of critical importance in the pathway.

1. glycolysis, an enzymatic path in the cytosol
2. tricarboxylic acid cycle, an enzymatic path in the mitochondrial matrix
3. electron transfer system, an electronic path in the mitochondrial inner membrane
4. oxidative phosphorylation, a proton driven ATP synthesis between the intermembrane space and the matrix of the mitochondrion.

We also saw that this pathway is a source of metabolites. To review all of this, I am showing here a figure you have already seen...

This pathway can be simplified in another pathway that I showed previously:

One alternative path is the Pentose Phosphate Pathway

As you can see above, in addition to the usual pathway for respiration, plants can carry out the Pentose Phosphate Pathway (sometimes called a "shunt"). This pathway should remind you of the Calvin Cycle of photosynthesis in certain ways. This pathway is not of major use in plants by any means, but is can be a source for intermediates as needed to "jump start" seedlings as they change over from the complete respiration dependency of subterranean existence to life in the light above the soil. This pathway is shown below: