Exploring the Amphipathic Nature of the Plasma Membrane

In summary, the amphipathic nature of the plasma membrane allows hydrophobic molecules to diffuse more easily than hydrophilic molecules. This is due to the fact that polar molecules are less favored to diffuse through a membrane than a lipid molecule.
  • #1
biophysics
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if the Plasma membrane is amphipathic (hydrophobic and hydrophilic), why does it only allow hydrophobic stuff to pass thru?
 
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  • #2
There are several mechanisms allowing material to cross the cell membrane. Simple diffusion is thought sufficient for small uncharged molecules- CO2, urea, ammonia; channels and trasporter proteins are used for ions and larger molecules like glucose. There is a water channel as well (aquaporin).

Even larger things are transported in via endocytosis.
 
  • #3
Thanks for the reply,

My question is about diffusion across membrane. Steroid hormones are able to diffuse while peptide hormone can't. If the membrane is amphipathic (hydrophobic and hydrophilic), why does it selectively allow hydrophobic stuff to pass thru? and not hydrophilic. Thanks
 
  • #4
Well water can diffuse through a membrane and it's pretty hydrophillic.

What you're really looking for though is unfavorable energetics. Polar molecules are far less favored to diffuse through a membrane than a lipid molecule.

And that stems from the fact that they are in solution. Polar and charged ions will be favored to stay in their current solvent or stick to the surface of the bi-layer since, in order to pass through, they would need energy to shed their solvent and their interactions with the charged phosphates on the surface so they could pass through.

Lipid molecules interact much more weakly even with like-minded molecules ... just through van der waal's. Therefore, they're not covered in a solvent shell, and it's not that much more unfavorable for them to pass through the charged phosphate layer than it was for them to pass through the water they were just in on the other side especially if it's down their concentration gradient. The van der waals forces that would "stick" them into the middle of the bilayer are also weak, so if there is a concentration gradient providing energy for diffusion all the way through, they'll diffuse.
 

1. What is an amphipathic molecule?

An amphipathic molecule is a molecule that has both hydrophilic (water-loving) and hydrophobic (water-fearing) regions. This means that one end of the molecule is attracted to water while the other end repels water.

2. How does the amphipathic nature of the plasma membrane contribute to its function?

The amphipathic nature of the plasma membrane allows it to act as a selective barrier between the cell and its surroundings. The hydrophilic heads of the phospholipids face outward towards the watery environment, while the hydrophobic tails face inward, creating a hydrophobic interior. This allows the membrane to regulate the movement of substances in and out of the cell.

3. What is the role of cholesterol in the amphipathic nature of the plasma membrane?

Cholesterol is a type of lipid that is present in the plasma membrane. Its hydrophobic nature helps to maintain the fluidity of the membrane by preventing the phospholipids from packing too closely together. This is important for the proper functioning of membrane proteins and the movement of substances across the membrane.

4. Can you give an example of a protein that utilizes the amphipathic nature of the plasma membrane?

One example is the sodium-potassium pump, which is a transmembrane protein that uses the difference in concentration of sodium and potassium ions to transport them across the membrane. This protein has both hydrophilic and hydrophobic regions that allow it to interact with the lipid bilayer and move ions against their concentration gradient.

5. How does the amphipathic nature of the plasma membrane differ in prokaryotic and eukaryotic cells?

In prokaryotic cells, the plasma membrane is typically made up of a single layer of phospholipids, making it more rigid and less fluid compared to the phospholipid bilayer of eukaryotic cells. Additionally, prokaryotic cells do not have cholesterol in their membranes, so they rely on other methods to maintain membrane fluidity, such as incorporating different types of lipids.

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