Question

When phospholipids are placed in water, why does a bilayer form?

• A. Phospholipids are naturally attracted to each other, forcing phosphate heads to face the aqueous areas.

• B. Lipids are hydrophilic and will from hydrogen bonds with the water, forcing the hydrophobic heads towards the middle of the bilayer.

• C. The polar tails will be attracted to the water and the nonpolar heads will be attracted to each other.

• D. The fatty acid tails are forced together away from the water, and water can create hydrogen bonds with the phosphate heads.

Answer 1

The correct option is D

Phospholipids, one of the key component of most of the cell membranes form bi layer in water because of their dual nature (amphipathy). The phosphate (PO43- ) head is electronegative, strongly polar group. This polar nature of phosphate head makes it extremely hydrophilic ( water loving) because of it's tendency to form hydrogen bond with water. However, the lipid tail is neither charged nor polar, so it can not form hydrogen bond with water and is hydrophobic and hence, moves away from water. Phosphate head moves towards the water and lipid tail moves away from water. Therefore, the bi layer formation happens because of dual nature of the phospholipid,

Option A is incorrect- Although there is attraction between two phospholipids but this interaction is not responsible for forcing or pushing the phosphate head towards water because the phosphate has an inherent polarity which makes it hydrophilic

Option B is incorrect as lipids are not hydrophilic but hydrophobic because they are non polar and hence they can not form hydrogen bond with water.

Option C is incorrect. In a phospholipid, the tail is made up of lipid which is hydrophobic not hydrophilic, because of it's non polarity.