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 + PO 4 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  /Life/memb.htm /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