Membrane Structure and Function

Membrane Structure and Function Membrane structure Traffic across the membranes

Membrane Structure • Fluid Mosaic Model • Made of lipids, proteins and carbohydrates • Mosaics of structure and function • Cell-to-cell recognition and carbohydrates

Membrane Structure • Proteins, by position 1) peripheral 2) integral: unilateral and transmemberane • Lipids 1) phospholipids 2) cholesterol • Carbohydrates

Protein Function • Transport • Enzymes • Receptor sites • Cell adhesion • Anchor for cytoskeleton • Cell-to-cell recognition • Anchor for ECM

Lipid Function • Phospholipids –amphipathic, bilayer, major structural component, barrier • Cholesterol – modulate fluidity

Carbohydrates • Cell-to-cell recognition • “Name tags” • Usually branched oligosaccharides • Sorting of embryonic cells • “Self” recognition

Traffic Across the Membranes • Membrane is selectively permeable • Passive transport • Active transport • Concentration gradient • Energy source

Passive Transport-I • Material moves down the gradient • Diffusion • Osmosis-water diffusion • Particles must be 1) small 2) nonpolar 3) uncharged

Passive Transport-II • Group translocation • Facilitated diffusion • Requires transport protein • Still down the gradient • Used for: 1) charged particles 2) LARGE particles 3) polar molecules

Osmosis • Water diffusion thru a membrane • Down the gradient • Hypertonic, isotonic, and hypotonic • Plasmolysis, turgor, crenation

Active Transport • cellular energy • Against the gradient • Ion pumps • Exocytosis and Endocytosis • Phagocytosis and pinocytosis • Receptor mediated endocytosis

Bulk Transport • Movement via vesicles • Exocytosis-out • Endocyctyosis-in

Videos and Websites • http://www.sumanasinc.com/webcontent/animations/content/endocytosis.html • http://www.johnkyrk.com/diffusion.html • http://www.youtube.com/watch?v=K7yku3sa4Y8&NR=1

Membrane Structure and Function