Factors affecting membrane structure and permeability

What is membrane fluidity important for

The fusion of membranes e.g. vesicles fusing with the plasma membrane.

The diffusion of new membrane components within the membrane.

The diffusion of components involved in signaling or metabolic reactions.

What are three factors that affect the fluidity of membranes

Temperature

Amount of cholesterol

Types of fatty acids in phospholipids

What type of phospholipids will make a membrane more fluid

Unsaturated lipids

Why are membranes containing a mix of saturated and unsaturated lipids more fluid

The molecules can pack less closely together so there are less hydrophobic interactions between the molecules holding them in place.

How does cholesterol maintain membrane fluidity at low temperatures

It prevents the regular packing of phospholipids so prevents freezing.

How does cholesterol maintain membrane structure at high temperatures

It interacts with the non-polar phospholipid tails so prevents it becoming too fluid.

Membrane structure in organisms that live at low temperatures

Phospholipids contain more unsaturated and/or shorter fatty acids to make make the membrane more fluid.

Membranes contain more cholesterol to help prevent the membrane freezing.

Membrane structure in organisms that live at high temperatures

Phospholipids contain more saturated and/or longer fatty acids to make the membrane less fluid.

Membranes contain more cholesterol to help maintain membrane structure and reduce fluidity.

How does temperature affect membrane permeability

As temperature increases, the phospholipids gain more kinetic energy and move more. This increases the fluidity and therefore permeability of the membrane.

What occurs to membrane proteins at high temperatures and how does this further affect membrane permeability

Membrane proteins become denatured and disrupt the membrane further increasing the permeability of the membrane.

What is the affect of organic solvents on membranes

They dissolve lipids and so damage cell membranes increasing permeability.