Question

A culture of bacteria growing at 45 degrees celsius was shifted to 20 degrees celsius. How would you expect this shift to alter the fatty acid composition of the membrane phospholipids. Explain.

Answer 1

Ans. The plasma membrane is a vital organelle of a cell as it facilitates various modes of transport across the membrane simultaneously with defining the boundary of the cell. Most of the functions of the membrane are attributed to its fluid nature. The fluidity of the membrane is kept at a relative constant level irrespective of the temperature.

Higher temperature provides higher kinetic energy to the constituent phospholipid molecules in the lipid bilayer. To prevent the membrane from disintegrating apart simultaneously with preserving the optimum fluidity, the cell has relative abundance of saturated and trans-configuration (in linear shape) in the phospholipids. It facilitates tight packing of the hydrophobic tails the hydrophobic core, the membrane and its fluidity is retained.

As temperature is lowered, the kinetic energy of fatty acid chains decrease. As a result, the membrane described above becomes more rigid or less fluid at lower temperature due to greater attraction among linear fatty acid tails.

To restore membrane fluidity at optimum level, the number of unsaturated as well as cis-configuration fatty acid in the phospholipids is increased. Relatively larger abundance of cis-configuration and unsaturated fatty acid in the phospholipids as well as steroids makes the membrane more fluid because both cis-form and unsaturation makes the chain irregular-shaped and hinders the closed packing of hydrophobic core. So, such membrane retain fluidity even at very low temperatures.

Therefore, decrease in the temperature shall possible increase the number of unsaturated and cis-configuration fatty acid chains in the membrane.