Question

based on their chemical structure, would phospholipids form a bilayer if they were in a hydrophobic substance like methane, rather than water? how would this affect membrane permeability?

Explanation:

1. Phospholipid Structure Recall: Phospholipids have a hydrophilic (polar, phosphate - containing) head and two hydrophobic (non - polar, fatty acid) tails. In an aqueous (water - based) environment, the hydrophilic heads face the water and the hydrophobic tails face inward, forming a bilayer.
2. Behavior in Hydrophobic Substance (Methane): In a hydrophobic substance like methane, the hydrophobic tails would be attracted to the methane, and the hydrophilic heads would repel the methane. So, instead of a bilayer, phospholipids would likely arrange themselves with the hydrophilic heads clustered together (to avoid the hydrophobic methane) and the hydrophobic tails facing outward (toward the methane). This arrangement would be the reverse of the bilayer in water.
3. Effect on Membrane Permeability:

• In a normal (aqueous - based) cell membrane (bilayer), the hydrophobic interior (tails) restricts the passage of hydrophilic molecules (like ions, polar molecules) and allows non - polar molecules to pass relatively easily.
• If the phospholipids form a reverse arrangement in a hydrophobic environment (heads clustered, tails outward), the "interior" of the "membrane" (now the clustered hydrophilic heads) would be polar. This would allow hydrophilic substances to pass more easily through the membrane, while hydrophobic substances would have more difficulty. The overall permeability of the membrane would be altered, with an increased permeability to hydrophilic molecules and a decreased permeability to hydrophobic molecules compared to the normal cell membrane in water.

Answer:

• Bilayer Formation in Methane: Phospholipids would not form a bilayer in a hydrophobic substance like methane. Instead, they would likely arrange with hydrophobic tails facing the methane (outward) and hydrophilic heads clustered together (inward), opposite to the bilayer arrangement in water.
• Effect on Membrane Permeability: The membrane (formed in methane) would have increased permeability to hydrophilic molecules (since the interior - like region is polar, from clustered hydrophilic heads) and decreased permeability to hydrophobic molecules (as the outward - facing tails are hydrophobic, but the "barrier" for hydrophobic molecules would be the polar head region) compared to a normal cell membrane in water.