Membrane Structure & Function Chapter 7: Membrane Structure & Function

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 Peripheral proteins: surface Membrane carbohydrates: cell-cell recognition Oligosaccharides (markers) Glycolipids, glycoproteins

Membrane structure, III Membrane protein function: Transport enzymatic activity signal transduction intercellular joining cell-cell recognition ECM attachment

Animation: Membrane Selectivity Membrane traffic Passive transport: diffusion of a substance across a biological membrane without Energy Diffusion: tendency of molecules to move from areas of high to low conc. Concentration gradient Osmosis: the diffusion of water across a selectively permeable membrane Animation: Membrane Selectivity Animation: Diffusion

Water balance Osmoregulation: control of water balance Hypertonic: higher concentration of solutes Solutes bind water, lower water potential (conc.) Water will move into the hyper solution to dilute it (increase its water conc.) Hypotonic: lower concentration of solutes Has higher water potential, more free water, loses water Isotonic: equal concentrations of solutes

Video: Paramecium Vacuole Water Balance Cont. Pay attention to reference point for –tonics Saltwater is hypertonic to fish cells, so water leaves the cells BUT fish’s cells are hypotonic to saltwater as well Water moves to lower water potential (MORE concentrated solution) More solute = lower potential Video: Chlamydomonas Video: Paramecium Vacuole

Water Balance Cont. Cells with Cell Walls: Turgid (very firm, pressurized) … Due to hypertonic cells Flaccid (limp) … Due to hypotonic cells Plasmolysis: plasma membrane pulls away from cell wall (bad) Video: Plasmolysis Video: Turgid Elodea Animation: Osmosis

Specialized Transport Transport proteins Facilitated diffusion: movement of ions and molecules down the conc. gradient via transport proteins Active transport: movement of substance against the conc. gradient with the help of cellular energy

Types of Active Transport Sodium-potassium pump Exocytosis: secrete macromolecules via fusing vesicles w/ plasma membrane Endocytosis: import macromolecules by forming new vesicles w/ plasma membrane phagocytosis pinocytosis receptor-mediated endocytosis (ligands) Active Transport Exocytosis Phagocytosis Exo and Endocytosis Introduction Receptor-Mediated Endocytosis