Question

How would a variation in fatty acid chain length and saturation affect the fluidity of a membrane. Describe how a glycerophospholipid and a sphingolipid would be positioned in this membrane.

Answer 1

Membrane fluidity refers to the viscosity of the lipid bilayer of a cell membrane. Viscosity of the membrane affects the diffusion of proteins and other bio-molecules within membranes and hence affects the functions of these things.
Membrane fluidity can be affected by factors such as heat, membrane fluidity can be increased by heating up the membrane. Also the composition of a membrane affects its fluidity because of the intermolecular interactions between the phospholipids tails add rigidity to the membrane as a result, the longer the phospholipid tails, more the interactions between the tails are possible and less fluid the membrane will be.
Also the degree of saturation of fatty acid tails affects the membrane fluidity. Phospholipid tails can be saturated or unsaturated ( saturated tails have no double bonds and are straight, Unsaturated tails have double bonds and are crooked) saturated fatty acids tails are arranged such that they maximize the interactions between tails and these interactions decrease bilayer fluidity. Unsaturated fatty acids have more distance between tails and thus fewer intermolecular interaction and more membrane fluidity.

Glycerophospholipids are considered as the main constituents of membrane bi layer. They are also termed as phosphoglycerides. Glycerophospholipids consist of three major constituent groups, three carbon glycerol back bone, two long chain on fatty acids that are esterified to first and second carbon atoms of the glycerol backbone and phosphoric acid that is esterified into the final carbon atom .

Sphingolipids are the ones that associate the cell membrane .They contain organic aliphatic amino alcohol sphingosine and a complex or simple sugar that is attached to the first carbon of the alcohol group.