Degree of unsaturation and cell fluidity

[Longcatislong]

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Somehow I managed to get a bit muddled about this concept.

Can someone clarify this concept for me:

When a cell is placed into very high temp conditions, the degree of unsaturation in the plasma membrane will increase, so that its melting point increases and fluidity of the membrane decreases. Right? I feel like I've read also read before that under these conditions fluidity should also increase...

 

[IsaacYankem]

Somehow I managed to get a bit muddled about this concept.

Can someone clarify this concept for me:

When a cell is placed into very high temp conditions, the degree of unsaturation in the plasma membrane will increase, so that its melting point increases and fluidity of the membrane decreases. Right? I feel like I've read also read before that under these conditions fluidity should also increase...

Where did you get this from?

My understanding is that saturated fatty acids pack more tightly and thus have higher M.P. than unsaturated fatty acids. The double bonds in unsaturated fatty acids provide a kink, preventing the membrane from packing too tightly and thus more fluid like.

Also, cholesterol in animals (sterols in plants) play an integral role in regulating membrane fluidity. At high temperatures, the membrane becomes too fluid-like, so cholesterol acts to provide rigidity to the membrane.

Conversely, at low temperatures, the membrane becomes too rigid, and cholesterol here will act to increase fluidity.

 

[FeralisExtremum]

Here's what I have on the topic in my notes:

"Note on lipids in membranes: Cell membranes need to maintain a certain degree of fluidity and are capable of changing membrane fatty acid composition to do so. In cold weather, to avoid rigidity, cells incorporate more mono and polyunsaturated fatty acids into the membrane as they have lower melting points and are kinked to increase fluidity. Warm weather climates show the opposite trend. Unsaturated fatty acids have higher boiling point but lower melting point compared to saturated fatty acids. This is due to increased "kinks" in packing of the molecules as a result of the double bonds. Double bonds increase bond polarity, increasing boiling point due to polarity but decreasing melting point due to less efficient packing.

Cholesterol also has a role: it adds rigidity to the membrane of animal cells under normal conditions (but at low temperatures it maintains its fluidity)"

So basically confirming what Isaac said.

 

[w4nt2baDDS]

I know this thread is old, but it ties into the current question I have.

I understand how saturation and unsaturation fatty acids affect membrane fluidity and melting points but I did not realize the cells could really adapt to the changes in temp.

Cell membranes need to maintain a certain degree of fluidity and are capable of changing membrane fatty acid composition to do so.

Is this true for all organisms? Or is this just for bacteria?

I can see how this could be useful for cold blooded organisms but for endotherms I would think the membrane fluidity would need to stay rather constant.

 

[FeralisExtremum]

Is this true for all organisms? Or is this just for bacteria?

I can see how this could be useful for cold blooded organisms but for endotherms I would think the membrane fluidity would need to stay rather constant.

Good question! This is true for all organisms (warm-blooded eukaryotes included) regardless. But your observation about warm-blooded vs cold-blooded is a good one. Since warm-blooded animals have an internal heating system, they tend to have less cholesterol in their membranes than cold-blooded animals because they do not need to counter as severe temperature fluctuations. Nonetheless, there is still some membrane fluidity.

 

[w4nt2baDDS]

That's just awesome.

Thanks for clearing that up!