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Did/Do you know...?

Today, I wanted to experiment with a more free-form way about little science factoids that may seem surprising. Today:

Schematic of a cell membrane.
Source: http://library.thinkquest.org/


Did/Do you know…what cell membranes are made off?

If you go back to your high school or basic college biology class, you may recall a picture showing that cell membranes are made off phospholipids.

All major examples taught in class – from animal, plants and microbial cell membranes to organelle membranes such as mitochondrial or ER membranes. The arrangement of phospholipid layers made complete sense: the lipid hydrophobic tails would be hidden within the bilayer of phospholipids while the polar hydrophilic heads would be facing the aqueous environment. For some reason, my brain made the connection: ALL membranes consist of phospholipids, but are they?

Apparently, this is not so when it comes to membranes of photosynthetic membranes according to the article titled “What Can Plant Models Teach Us About Lipid Trafficking?” written by Christoph Benning in ASBME Today. Instead, these membranes consist of galactoglycerolipids – or sugar lipids in other words.
Why do these membranes consist of sugar lipids rather than phospholipids you ask? Benning answers that when it comes to non-mobile plants (and aquatic environments for that matter), phosphorous used to be a precious and rare resource within the cell (before we started using synthetic fertilizers and using the oceans as dumps for unused phosphorous that is). Judicious use of this resource for other components such as energy transfer and copying of the cellular information material (DNA) had to be prioritized over other uses. Evolution responded by using galactoglycerolipids to conserve phosphorous.

What’s even more interesting is that the chloroplast has exported most of its DNA into the cell nucleus. In order for galactoglycerolipids to be assembled on the surface of chloroplasts, both the cell and the organelle have to work together to transport the lipid pre-cursors through multiple membranes to the chloroplast. How that’s done, however, remains a largely unknown mystery.

For tonight though, what I learned is: don’t let the brain fool you into a pattern. Question the obvious. The answers one gets may be surprising. And that wraps up tonight’s science factoid

Cited Literature:

Christoph Benning (2010). What Can Plant Models Teach Us About Lipid Trafficking?
ASBMB Today, April 2010, p.36

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