Phospholipid Layers

Phospholipids are important structural components of cell membranes (bilayers)

The presence of a phosphate group (PO4 3-) causes polarity of the molecule

The addition of the charged group makes a polar (hydrophilic) 'head' and two non-polar (hydrophobic) 'tails'

Formation of phospholipid bilayers

Amphipathic molecules tend to arrange themselves in aqueous solutions

--> their non-polar regions are directed toward the wat and can form hydrogen bonds with it

Phospholipids forma double layer (bilayer), where hydrophobic fatty acid tails extend towards each other

--> this is to keep away from the watery solutions inside and outside the cell

This forms the foundation of a plasma membrane

The cell membrane is a fluid spotted with proteins

The heads of the phospholipids have phosphate groups making them hydrophilic or polar

These sections are orientated towards the tissue fluid and cytoplasm (composed of polar and water molecules) on opposite sides of the membrane

The phosphate group and the fatty acid tails are connected by glycerol

The fatty acid tails are non-polar, hydrophobic and repel water

This creates a barrier between the internal and external watery environments of the cell

This prevents the movement of charged molecules as these are hydrophilic and therefore are repelled

In addition, the fatty acid tails are attracted to each other via weak forces of attraction

This gives some stability is further increased by the presence of cholesterol molecules which interact with the phospholipids

The phospholipid bilayer's chemical properties allow some molecules pass easily

Others need a special type of transport systems

Hydrophobic (non-polar) molecules can pass easily through the phospholipid bilayer as the interior of the cell membrane is also hydrophobic

Hydrophilic (charged or polar substances) need special transport

Nonpolar steroids pass through the phospholipid bilayer

Steroids are a group of lipids which all have four fused rings of carbon atoms

There are many different types a lot of which form hormones

They are all hydrophobic and can easily pass through cell membranes

They are used as chemical messengers around the body