Functions of Cell (Plasma) Membrane Protective barrier Regulate transport in & out of cell (selectively permeable) Allow cell recognition Provide anchoring sites for filaments of cytoskeleton

Cell membranes help organisms maintain homeostasis by controlling what substances may enter or leave the cells.

Photograph of a Cell Membrane

Membrane Components 3) Proteins (peripheral and integral) http://www.youtube.com/watch?v=moPJkCbKjBs 3) Proteins (peripheral and integral) 1) Phospholipids 2) Cholesterol

Phospholipids Make up the cell membrane Contains 2 fatty acid chains that are hydrophobic Head is hydrophilic & contains a –PO4 group & glycerol

FLUID MOSAIC MODEL FLUID- because individual phospholipids and proteins can move side-to-side within the layer, like it’s a liquid. MOSAIC- because of the pattern produced by the scattered protein molecules when the membrane is viewed from above.

Cell Membrane Polar heads are hydrophilic “water loving” Nonpolar tails are hydrophobic “water fearing” Makes membrane “Selective” in what crosses

Semipermeable Membrane Small molecules and larger hydrophobic molecules move through phospholipid bilayer easily. Examples: O2, CO2

Semipermeable Membrane Ions, hydrophilic molecules larger than water, and large molecules such as proteins do not move through the membrane on their own.

Check Point The cell membrane can be described as “selectively permeable”. What does that mean? What are the components of the cell membrane? Draw and label a phospholipid. Explain how the different parts make a cell selectively permeable. What types of molecules can easily pass through the cell membrane? Give an example. What types of molecules cannot move easily through the cell membrane? Give an example.

Passive Transport: the movement of substances across a cell membrane without the use of cell energy (ATP) down a concentration gradient Diffusion Simple Diffusion Facilitated Diffusion Osmosis

Concentration Gradient http://www.youtube.com/watch?v=JShwXBWGMyY

Simple Diffusion The movement of molecules from an area of high concentration to an area of low concentration (high  low) Molecules tend to “spread out” Requires no energy Molecules that can dissolve in lipids (hydrophobic) can diffuse through the membrane Very small molecules that are not lipid soluble can also diffuse through the membrane (EX: O2 and CO2 )

Facilitated Diffusion Carrier proteins “help” molecules across the membrane down the concentration gradient Molecules that use facilitated transport: Polar molecules (amino acids) Some large molecules (glucose) Charged molecules (ions)

The carrier protein transports the molecule across the cell membrane A molecule outside the cell binds to a carrier protein on the cell membrane The carrier protein transports the molecule across the cell membrane The molecule is released from the carrier protein inside the cell http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.html

Osmosis The diffusion of water molecules across a cell membrane High concentration  low concentration Watch the animation: http://www.stolaf.edu/people/giannini/flashanimat/transport/osmosis.swf http://www.youtube.com/watch?v=w3_8FSrqc-I

SOLUTES SUCK Rule for Osmosis If the area outside the cell has more salt—then water will be sucked out of the cell

Cells in Different Solutions “Iso” means the same Solutes are in equilibrium

“Hypo” = less Cells may burst or “lyse”

“Hyper” = more Cell will shrink or die, plants wilt Q: Why is it dangerous to drink salt water? http://www.youtube.com/watch?v=6MWl3DCa2uM