00:01
So this is a rather simple question.
00:03
Proteins do not pass through plasma membranes because plasma membranes are a semi -permeable barrier.
00:11
And so they regulate, or rather there is some level of regulation just within the physical attributes of the membrane itself that keeps some things from crossing the membrane barrier.
00:24
And most succinctly, we know that the molecules that tend to be allowed to diffuse across.
00:31
The plasma membrane are quite small.
00:35
And small isn't a great descriptor because, you know, it's very relative, but we'll get to that in a second.
00:41
They have to be small and they have to be relatively non -polar.
00:47
All right.
00:47
And so keeping these two things in mind, something like oxygen, talk about oxygen is on the order of two molecules.
00:57
I mean, we can just simplify this discussion to the number of molecules that something's made up of...