Question

To the right is a liposome - a hollow sphere made up of a lipid bilayer (like a cell) but without any membrane proteins. Of the listed molecules, which, if any, would you expect would be able to freely move (diffuse) across the membrane (based on their size and polarity)? Choose ALL that would cross.

a) chloride ion (small, polar)

b) fatty acid (medium, nonpolar)

c) glucose (medium, polar)

d) nitric oxide (small, nonpolar)

e) sodium ion (small, polar)

Answer 1

In general most of the membranes are semipermeable lipid bilayers. As the membranes are made of phospholipids which are hydrophobic in nature only lipid soluble moclues can easily and freely move or pass through the lipid bilayers.

B.Fatty Acid (medium and nonpolar)- can cross the membrane freely because FA is having a property of low solubility in water and highly hydrophobic in nature(molecules which repellent to the water) so FA binds rapidly with the phospholipids bilayers.

D.nitric oxide(small and nonpolar)-it is a hydrophobic molecule and size of the molecule is small and lipid soluble molecule so it can easily and rapidly passes through the lipid by later

Other options like A,C,E are having low membrane permiability since these are ions(membrane impermiable) and large polar molecules which are having less soluble with lipid molecules and cannot pass through the lipid bilayers membranes.

Since chloride ions and sodium ions are ions which are membrane impermiable with the help of transporters they can cross the lipid bilayers. But they cannot cross the lipid bilayers freely with out a transporters. Glucose is a polar molecules since lipid are hydrophobic in nature they are also having less permiability.