AP Biology The Cell Membrane

AP Biology Overview  The cell membrane separates the inside of a living cell from its surroundings  Function to maintain the homeostasis of the cell  The cell membrane is selectively permeable.  allows some substances to cross more easily than others, and some not at all.  Made primarily of phospholipids, with proteins & other macromolecules throughout.

AP Biology Phospholipids Fatty acid Phosphate  Fatty acid tails  hydrophobic  Phosphate group head  hydrophilic  Arranged as a bilayer

AP Biology Phospholipid bilayer polar hydrophilic heads nonpolar hydrophobic tails polar hydrophilic heads

AP Biology In and Out  Reminder: It is selectively permeable.  Only certain things can pass through the phospholipid bilayer:  Pass through easily  Small, non-polar (hydrophobic) substances  Ex: CO 2 and O 2  Do not pass through easily  Polar (hydrophilic) substances  Ex: Water, Sugar, Ions  Large molecules

AP Biology More than lipids…  Membrane proteins are inserted into the phospholipid bilayer  Fluid Mosaic Model  Fluid  flow  Mosaic  made of smaller parts It’s like a fluid… It’s like a mosaic… It’s the Fluid Mosaic Model!

AP Biology Membrane is a collage of proteins & other molecules embedded in the fluid matrix of the lipid bilayer Extracellular fluid Cholesterol Cytoplasm Glycolipid Transmembrane proteins Filaments of cytoskeleton Peripheral protein Glycoprotein Phospholipids

AP Biology Membrane Proteins  Proteins determine membrane’s specific functions  cell membrane have unique collections of proteins  Membrane proteins:  peripheral proteins  loosely bound to surface of membrane  cell surface identity marker  integral proteins  penetrate lipid bilayer  transmembrane protein go all the way through  transport proteins  Channels and pumps

AP Biology NH 2 H+H+ COOH Cytoplasm Retinal chromophore Nonpolar (hydrophobic)  -helices in the cell membrane H+H+ Porin monomer  -pleated sheets Bacterial outer membrane proton pump channel in photosynthetic bacteria water channel in bacteria Examples

AP Biology Many Functions of Membrane Proteins Outside Plasma membrane Inside Transporter Cell surface receptor Enzyme activity Cell surface identity marker Attachment to the cytoskeleton Cell adhesion

AP Biology Any Questions??