Please help to describe the following items in 23 sentences

Please help to describe the following items in 2-3 sentences each \"In your own words\"

1) What is the fluid mosaic model?

2) How does temperature impact membrane fluidity?

3) How does cholesterol impact membrane fluidity?

4) How does fatty chain saturation/unsaturation impact membrane fluidity?

5) Which types of molecules can cross the membrane by simple diffusion?

Solution

1)

The arrangement and interactions of membrane lipids and proteins can be described by ‘Fluid Mosaic Model’. The fluidity exhibited by artificial bilayers invitro experiments suggested that biological membranes can also have the similar properties.

This model was suggested by S. Jonathan Singer and Garth Nicolson. The fluid mosaic model gives the idea that integral proteins are visualized as the ‘icebergs’ floating in the ‘sea’ of two dimensional lipids and exhibits the mosaic distribution of integral and peripheral proteins.

2)

The fluidity of a bilayer depends on its transition temperature. The change in the transition temperatures alters the fluidity of the bilayer. Cooling of bilayer below its characteristic transition temperature results in solid gel like bilayer, losing its fluidity. Above the transition temperature the lipids are highly mobile and disordered in different directions and form liquid crystals. The bilayers are thicker in gel state than in liquid crystal state due to rigidity of hydrocarbon tails at low temperatures.

3)

Cholesterol also decreases the membrane fluidity due to its rigid steroid ring structure. It interferes with the movement of fatty acid side chains in the membrane lipids. It also alters the phase transition by broadening the temperature range. This is due to inhibitory action of Cholesterol on ordering of fatty acid side chains by fitting in between them. Hence, Cholesterol acts as a membrane plasticizer.

4)

The unsaturation of fatty acids determines the fluidity of bilayer. The transition temperature of a bilayer increases with the length of the chain and degree of saturation of fatty acid residues. The transition temperature of a bilayer generally ranges from 10 - 40C and transition temperature of the lipid bilayer decreases with the degree of unsaturation.

5)

Nonpolar molecules such as Steroids and O₂ readily diffuse through biological membranes by nonmediated simple diffusion according to the concentration gradient across the membranes.