Question

The fluidity of the lipid side chains in the interior of a bilayer is generally DECREASED by: A. an increase in temperature. B. an increase in fatty acyl chain length. C. an increase in the number of double bonds in fatty acids. D. the binding of water to the fatty acyl side chains E. none of the above or multiple of above is correct.

Answer 1

Fluidity of Lipid bilayer :

A) An increase in temperature increases the fluidity the Lipid side chains in the interior of Lipid bilayer. As temperature is increased and goes above T_m (Melting temperature), the Lipid layer loses it's rigidity(bonding strength weakens) and fluidity increases with the increase in temperature.

B) An increase in fatty acyl chain length decreases the fluidity of the lipid side chain bilayer. Long fatty acid hydrocarbon chains have stronger interaction between each other compared to the shorter ones. The free energy of the interaction is stabilizing and in the adjacent chains stay in closer contact. Thus increases the rigidity of the Lipid bilayer and hence decreases it's fluidity.

C) An increase in the number of double bonds also increases the fluidity of the Lipid chains in the bilayer. The unsaturated chains stay in bend structures and repel the Lipid side chains. Thus lipid chains are pushed far apart and the melting temperature, T_m, gets decreased, resulting in increasing the fluidity of the lipid side chains in the lipid bilayer.

D) Lipids have a Hydrophobic and a hydrophilic part. Also they are insoluble in water. The Hydrophobic(water repellent) parts of the lipid side chains are oriented towards the interior of the lipid bilayer. Therefore, binding of water to the fatty acyl side chains increases the fluidity of the lipid side chains. Lipid chains are repelled by water(lowers the attractive forces), bound to fatty acyl side chains, and thus gets far away from each other and so fluidity increases.

E) Only one of the above options are correct (not multiple options). So option E is incorrect.

Therefore, the correct option here, is B.