- All prokaryotic and eukaryotic cells are enclosed by an elastic thin covering calledPlasma membrane.It is selective permeable membrane because it only allows specific substances to pass through.Eukayotic cells in addition possess intracellular membranes collectively called asCytoplasmic membrane.These membranes are collectively called as Biological membranes.
Cell membrane by Dhatfield (CC BY-SA) derived from work of LadyofHats
Fluid mosaic model:
Singer and Nicholson in 1972 proposed this model.According to this model cell membrane is a ausifluid structure.Membranes are made up of lipids and proteins.It is said to be the model of membrane is viewed as a two dimensional mosaic of phospholipids and protein molecules.
- Lipids:The lipid molecules form a continuous bilayer.The protein molecules are arranged as extrinsic proteins(on the surface of the lipid bilayer) and intrinsic proteins(that penetrates the lipid bilayer either fully or partially).They are amphipathic ( has both hydrophilic and hydrophobic part).So that lipid molecule can pass through the lipid bilayer but not water soluble substances.Presence of specific type of membrane proteins permits each type of membrane to carry out distinctive functions.
- Proteins:Proteins are arranged in two forms:Extrinsic or peripheral proteins(Attached to either sides of the face of lipid bilayer and easily removable by light pressure) and Intrinsic or Integral proteins(Proteins that are penetrate wholly or partially by strong bonds and disruption occurs when we try to remove this type of protein).
Functions of Plasma membrane:
- Transporting nutrients into and wastes out of the cell.
- Intracellular and extra cellular transports are regulated by plasma membrane.
- Place for catalytic reaction of enzymes which has difficulty in aqueous environment.
- It also contains receptor protein that binds specifically to hormones.
- It separates the contents of cell from its outside environment and regulates what is entering and exiting the cell.
- Plasma membrane plays a vital role in protecting the integrity of interior of the cell by allowing only some selected substances into the cell and also helps in maintaining the shape of the cell.
- Cell membrane is primarily composed of lipids and proteins. In this, proteins monitor and maintains the cells chemical climate and assist in transfer of the molecules across the membrane while lipids helps to provide membranes flexibility.
- The lipid bilayer is semi-permeable, which allows only some selected molecules to get diffused across the membrane.
Characteristics of Plasma Membrane :
- The plasma membrane or cell membrane is made up of two layers of the phospholipids.
- Plasma membrane contains many proteins embedded into it.
- The plasma membrane do the regulation of entry and exits from the cell, Many molecules crosses the cell membrane via osmosis and diffusion.
- The fundamental structure of cell membrane is phospho lipid bilayer it forms a very stable barrier between the two aqueous compartments.
- The proteins present in the plasma membrane, acts as pumps, receptors, channels, enzymes or structural components.
Components of Plasma Membrane :
- Proteins such as glycoprotein, which are useful for cell recognition and acts as antigens and receptors.
- Proteins such as glycolipids are attached to phospholipids along with the sugar chains.
- Lipids with small chain of carbohydrates are attached on the extracellular side of the membrane.
- Phospholipid Bilayer – which are made up of lipids and phosphates. These create a partially permeable membrane, which allows only certain limited substances to diffuse through the plasma membrane.
- Cholesterol – it maintains fluidity of the cell surface membrane.
Plasma Membrane Strcuture :
- It is a boundary, which separates the living cell from their non-living surrounding environment.
- It is the phospholipids bilayer.
- This membrane is an amphipathic, which contains both hydrophilic heads and hydrophilic tails.
- It is a fluid mosaic of proteins, lipids and carbohydrate.
- It is a lipid bilayer, which comprises – two layers of phospholipids, phosphate head is polar (water loving), fatty acid tails non-polar (water hating) and proteins embedded in the membrane.