9700 · 4.1
Fluid mosaic membranes
Every living cell is encased in a remarkable structure: the **cell surface membrane**. Far from a simple, static boundary, it's a dynamic, intricate barrier known as the **fluid mosaic membrane**. This model, proposed by Singer and Nicolson in 1972, explains how the membrane's components are arranged and how they work together to control what enters and leaves the cell, facilitating communication and maintaining cellular integrity. Let's delve into its fascinating structure and function.
Need to know
What you need to know
- The membrane is 'fluid' because phospholipids and proteins can move laterally.
- It is a 'mosaic' because proteins are scattered throughout the bilayer like tiles.
- The phospholipid bilayer forms a barrier to water-soluble substances due to its hydrophobic core.
- Cholesterol in animal cells regulates fluidity, preventing the membrane from becoming too fluid at high temperatures or too rigid at low temperatures.
- Intrinsic proteins are embedded in the bilayer and can act as channels or carriers for transport.
- Extrinsic proteins are on the surface and can be enzymes or provide structural support.
- The glycocalyx (glycoproteins and glycolipids) is on the outer surface and is vital for cell recognition, adhesion, and as receptors.
- Membrane fluidity is increased by higher temperatures, shorter fatty acid tails, and a higher proportion of unsaturated fatty acid tails.
Explanation
Fluid mosaic membranes
- The membrane is 'fluid' because phospholipids and proteins can move laterally.
- It is a 'mosaic' because proteins are scattered throughout the bilayer like tiles.
- The phospholipid bilayer forms a barrier to water-soluble substances due to its hydrophobic core.
- Cholesterol in animal cells regulates fluidity, preventing the membrane from becoming too fluid at high temperatures or too rigid at low temperatures.