 Regulates what enters and leaves the cell, provides protection and support  Double layered sheet called a LIPID BILAYER

 The control of particle movement across the membrane  Some substance pass freely through the membrane : water, glucose, oxygen  Some substance pass with effort or require energy: charged ions like Na or K  Other substances are not allowed to pass at all: large proteins or starch

 There are so many different kinds of molecules in the membrane that it is called a “mosiac”  Often called a fluid mosiac model.

 Integral Proteins - permanently connected to the cell membrane, large sections embedded in the hydrophobic (middle) layer of the membrane ◦ Form protein channels ◦ Most common type of protein ◦ Receptors ◦ Help in cell adhesion

 Channel Proteins - amphipathic proteins (one end polar one end nonpolar) that allow for ions to pass through the membrane down their concentration gradient  Structural Proteins - these proteins anchor to surfaces and help with cell-cell adhesion  Transport Proteins - proteins that change shape when they bind to a substrate and help facilitate diffusion of substances down their concentration gradient

 Peripheral Proteins - not bonded as strongly to the membrane, may be attached to integral protein or sit on the surface ◦ Can help with transport ◦ Enzymes ◦ Target for toxins 

 Proteins on the outer surface act as recognition molecules to help the organism recognize its own cells.  Proteins on the inner surface provide anchorage points for the cytoskeleton

 Link to Cell Membrane Link to Cell Membrane So we built it, now what can it do????????

 movement of molecules across the cell membrane and does not require energy  dependent on the permeability of the cell membrane  There are three main kinds of passive transport – ◦ Diffusion ◦ Osmosis ◦ Facilitated Diffusion

 CONCENTRATION: Mass of solute/volume of solution  Concentration gradient: the difference in concentration between a region of high concentration and a region of lower concentration ◦ (high concentration) – (low concentration) EQUILIBRIUM: when the concentration of the solute is the same throughout the system

 DEFINITION: the movement of particles from an areas where they are more concentrated to an area where they are less concentrated  diffusion animation diffusion animation  EQUILIBRIUM: when the concentration of the solute is the same throughout the system

 Dialysis tubing Dialysis tubing

 NO ENERGY IS USED ◦ Diffusion is based on random movement of molecules to reach equilibrium  EVEN AT EQUILIBRIUM THE MOLECULES ARE STILL MOVING!!

 1) Diffusion –  2) Osmosis

 DEFINITION – the diffusion of WATER through a selectively permeable membrane  In order to obtain EQUILIBRIUM, the water will cross from a high WATER concentration to a low water concentration.  Water molecules can cross a membrane that large molecules may not be able to cross.

lettuce entertain you....

 ISOTONIC – both sides of the membrane have equal concentrations, it has reached equilibrium  HYPERTONIC – a higher solute concentration  HYPOTONIC – a lower solute concentration

osmosis working

 What does this mean to the cell??? ◦ Organisms MUST maintain osmotic pressure to survive Osmotic pressure – definition – the increase in pressure resulting from the flow of water in osmosis

 THINK EGGS!

 NO ENERGY!!!!  MOVEMENT OF WATER ACROSS A SELETIVELY PERMEABLE MEMBRANE – JUST WATER!!!!!!  ISOTONIC  HYPERTONIC  HYPOTONIC

 1) Diffusion –  2) Osmosis  3) Facilitated Diffusion

 DEFINITION - Movement of specific molecules across cell membranes through protein channels  NO ENERGY IS USED!  Works ONLY in the direction of the concentration gradient (high to low concentration)  Membrane proteins are specific for the molecule

facilitated diffusion

 NO ENERGY!!!  Need a membrane protein to “help” the molecule across the membrane  Works WITH concentration gradient