Cell Membranes

Semi-permeable

Lipid bilayer

Function of Plasma Membrane Physically separates cell from outside world

Maintains homeostasis

Regulates passage of materials into and out of cell

Endomembrane System Membranes of organelles such as:

Nuclear membrane Endoplasmic Reticulum Golgi Complex Vesicles/Vacuoles Lysosome

Divide cell into compartments

Serve as surfaces for chemical reactions

Basic Structure of the Membrane

Made of phospholipids:

Hydrophilic head Glycerol + PO4

Hydrophobic tail 2 fatty acid chains

Since cells are in an aqueous solution, bilayer is most stable form

Additional Molecules

Fluid Mosaic Model Currently accepted molecule of plasma

membrane structure

Lipids of membrane are fluid and move laterally

Proteins are embedded/scattered throughout

http://home.earthlink.net/~shalpine/anim/Life/memb.htm

Membrane Proteins Arranged asymmetrically

2 main types:

Integral proteins May be transmembrane

Peripheral proteins

Functions of Membrane Proteins: Passive transport - passageways

Active transport – pump materials

Enzymes – catalyze reactions

Signal Transduction

Identification

Membrane Potential Cell membrane is polarized

Inside of cell is more neg. than outside Electrical gradient

Voltage Can be used to do work

Membrane potential = voltage Resting potential = -70mV

Cell Junctions Form between cells in

close contact with one another

Allow for rapid communication, prevent passage of material, form strong connections

Cell Junctions: Tight junctions

Gap junctions

Anchoring Junctions Desmosomes Adhering Junctions

Plasmodesmata