Lecture #3Date ______  Chapter 8~ Membrane Structure & Function

Voyage through a cell  4Fqpg 4Fqpg  Golgi  a4Y8 a4Y8

Choroplast and Mitochondrion

Cell Junctions

 Contractile vacuole:  COug4&NR=1 COug4&NR=1  Cilia and flagellates  UzwQ0 UzwQ0

Membrane structure, I  Selective permeability  Amphipathic~ hydrophobic & hydrophilic regions  Singer-Nicolson: fluid mosaic model

Membrane structure, II  Phospholipids~ membrane fluidity  Cholesterol~ membrane stabilization  “Mosaic” Structure~  Integral proteins~ transmembrane proteins  Peripheral proteins~ surface of membrane  Membrane carbohydrates ~ cell to cell recognition; oligosaccharides (cell markers); glycolipids; glycoproteins

Membrane structure, III  Membrane protein function: transport enzymatic activity signal transduction intercellular joining cell-cell recognition ECM attachment  Marker proteins are also membrane proteins

Questions Describe the polarity of an integral protein. Why does a protein for cell recognition never flip sides by going “inside-out”? Why can phopholipids switch places with their neighbor to the left and right, but not across from each other? Why is cholesterol located where it is in the plasma membrane?

Membrane traffic  Diffusion~ tendency of any molecule to spread out into available space  Concentration gradient: High to low  Passive transport~ diffusion of a substance across a biological membrane  Osmosis~ the diffusion of water across a selectively permeable membrane

Water balance  Osmoregulation~ control of water balance  Hypertonic~ higher concentration of solutes  Hypotonic~ lower concentration of solutes  Isotonic~ equal concentrations of solutes  Cells with Walls:  Turgid (very firm)  Flaccid (limp)  Plasmolysis~ plasma membrane pulls away from cell wall

Questions  Why do grocery stores spray their vegetables with water?  Why does your skin “prune” when you swim all day at the pool?  Why does your skin crack when you spend all day at the ocean?  Why do trees in the tropics have big leaves compared to dessert trees?  When a plant “wilts”, are its cells turgid or flaccid?

Specialized Transport  Transport proteins  Facilitated diffusion~ passage of molecules and ions with transport proteins across a membrane down the concentration gradient  Active transport~ movement of a substance against its concentration gradient with the help of cellular energy

Types of Active Transport  Sodium-potassium pump  Exocytosis~ secretion of macromolecules by the fusion of vesicles with the plasma membrane  Endocytosis~ import of macromolecules by forming new vesicles with the plasma membrane phagocytosis (eating) pinocytosis (drinking) receptor-mediated endocytosis

Video of the cell working  G5eSw&NR=1 G5eSw&NR=1

Receptor mediated endocytosis using coated pits  Multiple receptors  Concentrates molecules for endocytosis