Mitochondria-membranes

[G1SG2]

Okay, so we have the inner and outer membrane. From my understanding, the outer membrane is pretty permeable to things such as ions, ATP, and other nutrient molecules. However, the inner membrane is not very permeable, BUT I remember reading that it's freely permeable to stuff like CO2, H2O and O2? Or am I wrong?

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[Charles_Carmichael]

The permeability of the inner membrane really depends on what transporters are present; these transporters allow transport of stuff in a very controlled manner, unlike the outer membrane. The outer membrane has a lot of porins that pretty much allow anything below a certain size to travel across into the intermembrane space. The inner membrane lacks these nonselective porins.

CO2 and O2 are permeable through all membranes because they are lipid soluble (they're not polar). So they can traverse the lipid membrane with ease. Not sure about the H2O part though; my understanding is that the inner membrane is not that permeable to H2O. But I took biochem a year ago, so some of the finer details are a bit fuzzy on specific transporters, etc.; maybe someone else can also chime in?

 

[sv3]

The permeability of the inner membrane really depends on what transporters are present; these transporters allow transport of stuff in a very controlled manner, unlike the outer membrane. The outer membrane has a lot of porins that pretty much allow anything below a certain size to travel across into the intermembrane space. The inner membrane lacks these nonselective porins.

CO2 and O2 are permeable through all membranes because they are lipid soluble (they're not polar). So they can traverse the lipid membrane with ease. Not sure about the H2O part though; my understanding is that the inner membrane is not that permeable to H2O. But I took biochem a year ago, so some of the finer details are a bit fuzzy on specific transporters, etc.; maybe someone else can also chime in?

I don't think H20 freely diffuses but uses facilitated diffusion (channel proteins).