Factors affecting membrane permeability

how do solvents affect membrane permeability

• some solvents such as ethanol dissolve the lipids in the cell membrane and so the cell membrane loses it structure

• some solvents increase membrane permeability more than others

• increasing the conc of solvent will also increase membrane permeability

• any solvent less polar than water or non polar will disrupt the membrane

• Phospholipids make up the basic bilayer of the membrane. They are amphipathic (hydrophilic heads, hydrophobic tails). Organic solvents can disrupt the hydrophobic interactions between the tails, breaking apart the bilayer structure and increasing membrane permeability or even dissolving the membrane.

how do temperatures below 0’C affect membrane permeability

• the phospholipids dont have much kinetic energy so they can’t move very much, so they’re packed closely together and the cell membrane is rigid.

• channel proteins and carrier proteins in the membrane denature ( losing their structure and function) increasing the permeability of the membrane

• ice crystals may form and pierce the membrane making it highly permeable but when it thaws permability decreases again

how do temperatures between 0 and 45 degrees affect membrane permeability

• the phospholipids can move around and aren’t packed as tightly together, the membrane is partially permeable

• as the temp increases the phospholipids move more because they have more kinetic energy and this increases the permeability of the membrane as the phospholipids moving around more creates gaps in the membrane

how do temperatures above 45 degrees affect membrane permeability

• the phospholipid bilayer starts to melt and the membrane becomes more permeable

• water inside the cell expands putting pressure on the membrane

• channel proteins and carrier proteins in the membrane denature so they can’t control what enters or leaves the cell increasing the permeability of the membrane

Fatty acid composition of phospholipids:

• Saturated fatty acids → tails pack tightly → less fluid → lower permeability.

• Unsaturated fatty acids → kinks prevent tight packing → more fluid → higher permeability.

Cholesterol content

• Cholesterol molecules stabilise the membrane by preventing phospholipids from moving too much.

• Increases rigidity at high temperatures, prevents excessive fluidity, reduces permeability to small water-soluble molecules.