Chapter 10: Membrane Structure

CELL MEMBRANE:

• Cell Membranes are the outermost layer in animals whereas in plants the second most layer after the cell wall.

• It is the universal structure and structural cell membrane of prokaryotes that are similar to eukaryotes.

• It encloses the boundaries and all the cellular interactions between cytosol and the external environment.

• Cell Membranes are dynamic, fluid structures comprising lipid bilayers and protein molecules embedded in them.

• They are held together by non-covalent interactions.

  

LIPID BILAYER:

• The lipid bilayer comprises phosphoglycerides, sphingolipids, and sterols in the cell membrane.

• All lipid molecules have a hydrophilic head and two hydrophobic tails. This makes nature to be amphillic.

• Lipids are the main component of the cell membrane because it forms the continuous structural frame of the cell membrane.

• The phospholipid layer provides fluidity to the plasma membrane because phospholipids are rich in unsaturated fatty acids.

• The main phospholipids in most animal cell membranes are phosphoglycerides.

• Glycolipids and cholesterol are also part of the lipid bilayer.

• The reason behind the formation of the bilayers is their shape and amphiphilic nature.

• The lipid bilayer is a two-dimensional fluid.

• Liposomes (spherical vesicles) provide fluidity to the lipid bilayer.

• When the lipid molecules in the plasma membrane of living cells segregate in their specialized domains called lipid rafts.

• The excess lipids often get stored as fat droplets and these are often termed to be adipocytes.

• As the lipid bilayer is known to be asymmetrical which is functionally very important when it comes to converting extracellular signals into intracellular ones.

  

MEMBRANE PROTEINS:

• Membrane proteins are responsible for performing most of the membrane’s specific tasks.

• “A typical plasma membrane is somewhere in between, with protein accounting for about half of its mass”.

• Membrane proteins are amphiphilic having both hydrophobic and hydrophilic regions.

• Many of the membrane proteins also extend through the lipid bilayer called transmembrane proteins.

• Other membrane proteins are located entirely in the cytosol.

• There are membrane-associated proteins that do not extend into the hydrophobic interior of the lipid bilayer at all. These sorts of proteins are often referred to as peripheral membrane proteins.

• Only transmembrane proteins can function on both sides of the bilayer or transport the molecules across it.

• There are two types of protein that are present in the plasma membrane.

CARBOHYDRATES:

• Oligostructures of the glycolipids and glycoproteins on the outer surface of the plasma membrane are involved in cell to cell recognization mechanism.