membrain structures

A cell is composed of two distinctive environments, the hydrophilic aqueous cytoplasm and the hydrophobic lipid membranes.  The lipids environment is defined by how they react to different hydrophobic nature.  We are learning about three members, fats, phospholipids, and steroids.  Lipis are slightly soluble to insoluble in water.  They are hydrophobic because the molecules consist of long hydrocarbon backbones.  Lipids can serve as many functions in organisms.  They are the major components of waxes, pigments, steroid hormones, and cell membranes.  Fats, steroids, and phospholipids are very important to the function of membranes.



Fats are synthesized from two different classes of molecules. Fatty acids are normally 16-22 carbons long. Fatty acids can be two types; saturated and unsaturated. Saturated fatty acids never have a carbon to carbon double bonds.  When the unsaturated fatty acids have 2 to 3 carbon to carbon bonds.  Unsaturated fatty acids have lower melting points than saturated fats.
                                                          Phospholipids


                                           


Phospholipids contain 2 fatty acids attached to a glycerol head.  A condensation reaction makes this occur.  The third alcohol of the glycerol forms an ester bond through reaction with phosphoric acid.  this is another example of a condensation reaction between an acid and an alcohol with the release of water.  The head of the phospholipid is hydrophilic, where the fatty acid tail is hydrophobic.  In an aqueous solution they will self assemble into micelles or bilayers.

                                                    Steriods

Steriods are a family of lipids based on a molecule with four fused carbon rings.  In this family there is hormones and cholesterol.  Cholesterol is a component of the cell memorial in animals, it moderates the membrane fluidity because it restricts the motion of the fatty acid tails.
                                              Fluid Quality of Membranes
The cell membrane must be dynamic in order for the cells to grow.  To keep the membrane fluid at physiological temperatures the cell alters the composition of phospholipids. You have to have the right ration of saturated to unsaturated fatty acids in cell membranes.  A low number of unsaturated fatty acids helps maintain the fluid nature of the cell membrane without it becoming to liquid at body temperature.
                                                 Proteins
Cells need a way to communicate with other cells because the cell membrane is only semipermeable.  These roles are primarily filled by proteins.  Membrane proteins are classified into two major categories, integral proteins, and peripheral proteins. Integral membrane proteins are those proteins that are embedded in he lipid bilayer and are generally characterized by their solubility in non-polar, hydrophobic solvents.  Transmembrane proteins are examples of integral proteins with hydrophobic regions that completely span the hydrophobic interior of the membrane. The hydrophilic proteins are the proteins exposed to the interior and exterior of the cell.