Which of the following membranes would be most fluid Note Tr

Which of the following membranes would be most fluid? Note- Transition temp. increases with chain length and degree of saturation. Above transition, temp decreases fluidity. below transition temp increases fluidity.

a. One containing lipids with n-hexadecanoate chains.
b. One containing lipids with n-octadecanoate chains.
c. One containing lipids with cis,cis-9,12-octadecadienoate chains
d. One containing lipids with cis,cis-9,12-hexadecadienoate chains
e. They will all have the same fluidity.

Solution

As mentioned in the question, those lipids are fluid which have lesser number of carbon atoms and more the number of double bonds (UNSATURATION). Lipids with n-hexadecanoate and n-octadecanoate chains are saturated fatty acids while lipids with cis,cis-9,12-octadecadienoate (18C) and cis,cis-9,12-hexadecadienoate chains (16C) are unsaturated fatty acids. Therefore, we consider the latter two lipids as more fluid. Now, among the latter two, lipid with cis,cis-9,12-hexadecadienoate chain has lesser number of carbon atoms (16 C-atoms). Therefore, we can conclude that option-d is correct answer.