Standard B-2.2

 The process of maintaining balance in an organism’s internal environment.  Essential to the survival of a cell.  Maintaining homeostasis a primary job of the plasma membrane. (does this by being semipermeable)

 Defined as a flexible boundary between a cell and it’s environment.  ALL prokaryotic and eukaryotic cells have a plasma membrane to separate them from their watery environment.  The membrane allows nutrients into the cell and allows waste and other products to leave the cell.

 The plasma membrane has the property of selective permeability.  (also called semipermeable)  This is how homeostasis is maintained.  Means:  Allows some substances to pass through to the inside  Does not allow some substances to pass though to the inside  Doesn’t allow just anything to leave the cell either.  It is selective in what it lets enter and leave the cell

Fish net Coffee filter Flour sifter Gold Mining too

Most of the molecules in the PM are phospholipids.

 PM is composed of a phospholipid bilayer.  (2 layers of phospholipids are arranged tail-to- tail.)

 Each phospholipid is diagramed as a head with 2 tails.

 Heads:  made polar by the phosphate group  Is attracted to water bc water is polar too  Hydrophilic = water loving  Tails:  Nonpolar  Repelled by water  Hydrophobic = water fearing

 The layers make a sandwich so that the fatty acid tails make up the inner most portion of the PM.  Water loving heads are in contact with the water inside of the cell and the watery outside of the cell.  Water fearing tails are farthest away from the water they hate.  Not touching the water on the inside or the outside of the cell.

 Moving with and among the phospholipids are: - cholesterol - carbohydrates - proteins

 Cholesterol: -prevents the fatty-acid tails from sticking together. - contributes to the fluidity of the pm. (A high cholesterol diet is not advised, but cholesterol plays a critical role in membrane structure.)

 Carbohydrates: - Stick out from pm to define the cell’s characteristics - Helps cells identify chemical signals. (Carbs in membrane might help disease-fighting cells recognize and attack a potentially harmful cell.)

 Proteins: -2 types of proteins found in PM 1. peripheral proteins 2. integral proteins

 Peripheral proteins: proteins that do not protrude from the inside of the cell to the outside of the cell.  Outer surface: called receptors and they transmit signals from outside the cell to the inside of the cell  Inner surface: anchor the pm to the cells internal support structure, gives the cell it’s shape.

 Integral proteins: span the entire membrane, creating tunnels through which certain substances can enter and leave the cell.  Move needed substances in  Move wastes out Also called: Transport proteins

 The phospholipids in the bilayer create a “sea” in which other molecules can float, like apples floating in a barrel of water.  “sea” concept is the basis for the fluid mosaic model of the pm.  The phospholipids can move sideways w/i the membrane, just as the apples move around in the barrel.

 At the same time, other components in the membrane, like proteins, also move among the phospholipids.  Because there are different substances in the pm, a pattern, or mosaic is created on the surface.  The components of the pm are in constant motion, sliding past each other.

 Fluid: particles that can change position w/o separating.  Mosaic: picture or pattern made of small pieces of different colors and/or shapes.

 What is the main function of the Plasma Membrane?

 What name has been given to the sea-like movements of the plasma membrane?

 What does hydrophobic mean?

 Besides phospholipids, what is another structure you may see in a plasma membrane and what is that structures function within the membrane?

 What does hydrophilic mean?

 What do we call the 2 layers of phospholipids arranged tail to tail?