Question

How are newly synthesized phospholipids inserted into the bilayer leaflet? What happens to the lipid molecules after insertion?

1) They are inserted into the bilayer leaflet facing the cytosol and then translocated across the bilayer to the other leaflet by flippase enzymes.
2) They are inserted into the bilayer leaflet facing the extracellular space and then translocated across the bilayer to the other leaflet by flippase enzymes.
3) They are inserted into the bilayer leaflet facing the cytosol and then translocated across the bilayer to the same leaflet by flippase enzymes.
4) They are inserted into the bilayer leaflet facing the extracellular space and then translocated across the bilayer to the same leaflet by flippase enzymes.

Answer 1

Newly synthesized phospholipids are inserted into the cytosolic side of the bilayer leaflet and then moved across the bilayer to the opposite leaflet by flippase enzymes.

Step-by-step explanation:

Newly synthesized phospholipids are inserted into the bilayer leaflet facing the cytosol. After insertion, the lipid molecules can be translocated across the bilayer to the other leaflet by specialized enzymes known as flippases. Therefore, the correct answer to the student's question is that they are inserted into the bilayer leaflet facing the cytosol (1) and then translocated across the bilayer to the other leaflet by flippase enzymes.

The phospholipid bilayer forms the fundamental structure of the cell membrane, with hydrophilic heads facing the aqueous environments inside and outside the cell, while the hydrophobic tails face each other away from water. This arrangement provides the fluid, dynamic nature of cellular membranes. The flippase enzymes ensure that the phospholipids are evenly distributed between the two layers of the bilayer, maintaining the membrane's integrity and function.