Cell Membrane question

[BiomajorPreDent]

Ok, so destroyer says that proteins and lipids can not move from one face of the membrane to the other

but in my molecular bio class, they said that there are membrane protein flippase, that catalyze movement of phospholipids from one leaflet to the other.

It also says that this movement is energetically unfavorable since the polar head must get through the hydrophobic region.

So now I am confused. I know proteins and lipids can move laterally, but for the DAT, should I consider proteins and lipids to not move from one face of the membrane to the other? Or can phospholipids move but its just so rare that it doesnt happen?

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[peyman2002]

Ok, so destroyer says that proteins and lipids can not move from one face of the membrane to the other

but in my molecular bio class, they said that there are membrane protein flippase, that catalyze movement of phospholipids from one leaflet to the other.

It also says that this movement is energetically unfavorable since the polar head must get through the hydrophobic region.

So now I am confused. I know proteins and lipids can move laterally, but for the DAT, should I consider proteins and lipids to not move from one face of the membrane to the other? Or can phospholipids move but its just so rare that it doesnt happen?

just know that they need protein channels to allow them to move,hmm do lipid move thru protein channels?! thats kinda odd I think.I've never thought about that.oh I just remembered that lipid soluble molecules do pass thru membrane, also nonpolar molecules. I can't think of anything else.

 

[joonkimdds]

lipids don't need protein channels. They can go thru membranes and bind to receptors in cytoplasm or whatever. However, nonlipids need protein channels.

could u provide the # on destroyer that says lipids can't go thru membrane?

 

[uclaDDS101]

The OP is obviously talking about membranous proteins and phospholipids, both which are associated with one leaflet of the lipid bilayer. I'm sure the Destroyer is stating that the transfer of peripheral proteins and phospholipids from one leaflet to the other does not occur readily, since the transition state (polar molecule/functional group in a polar medium) is in a very high energy state (The reaction has a high activation energy). Thus, the use of an enzyme (e.g., flippase, floppase, scramblase, etc.) is required for the passage of the polar head through the bilayer. To the OP, the question is apparently asking if the protein or phospholipid can move through the membrane under normal conditions (without the aid of an enzyme).

 

[BaylorDDS]

Flippase moves lipids from one face of the membrane to the other, however it doesn't move proteins or carbohydrates, they stay where they are.

For the dat, this info in irrelevant, but you can still know the lipids move from one side to the other through an input of energy with flippase. The dat won't contradict more complicated mechanisms.

 

[BiomajorPreDent]

The OP is obviously talking about membranous proteins and phospholipids, both which are associated with one leaflet of the lipid bilayer. I'm sure the Destroyer is stating that the transfer of peripheral proteins and phospholipids from one leaflet to the other does not occur readily, since the transition state (polar molecule/functional group in a polar medium) is in a very high energy state (The reaction has a high activation energy). Thus, the use of an enzyme (e.g., flippase, floppase, scramblase, etc.) is required for the passage of the polar head through the bilayer. To the OP, the question is apparently asking if the protein or phospholipid can move through the membrane under normal conditions (without the aid of an enzyme).

Flippase moves lipids from one face of the membrane to the other, however it doesn't move proteins or carbohydrates, they stay where they are.

For the dat, this info in irrelevant, but you can still know the lipids move from one side to the other through an input of energy with flippase. The dat won't contradict more complicated mechanisms.

Thanks UCLA and Baylor, thats what I wanted to know.