mitocondria and myelin help

**ribeena12345** · 02-11-2009, 01:56 AM

hey. why is the composition of the inner mitocondrial membrane 75% protein and 25% lipid?

and why is the composition of the myelin sheath 20% protein and 80% lipid?

thanks!!!!!

**Frank E** · 02-11-2009, 05:25 PM

Don;t know.
Better dielectric?

**zhangyuzhi** · 02-11-2009, 05:50 PM

Originally Posted by ribeena12345

hey. why is the composition of the inner mitocondrial membrane 75% protein and 25% lipid?

and why is the composition of the myelin sheath 20% protein and 80% lipid?

thanks!!!!!

hi there. first of all I would refrain using the term "why" in this type of questions, but anyway, my intepretations:

1. The primary function of IMM is energy production, and which involves a massive variety and number of enzymes/receptors/channels- all proteins in nature. As these proteins are often associated with the lipid bilayer (transmembrane proteins, lipid anchored proteins etc.), they can be found in the lipid fraction of the cell preparations. This might explain the 75:25 ratio.

2. The primary function of myelin sheath is for electrical insulation, and high lipid content results in an aprotic environment . This results in lower capacitance (if you see the cell membrane as a capacitor) and by keeping current constant (ion flow), voltage charging is faster. This then gives the saltatory conduction observed in axons.

Since this is conferred by the lipid content, an explanation to the 20:80 ratio could be there...