Chapter 8 Membrane Structure and Function

Fluid Mosaic Model Fluidity: P.Membrane (PM) held together by weak hydrophobic interactions Lateral drifting ability – Lipids – Proteins: some stable/attached to cytoskeleton Temperature Dependent

“Mosaic” Protein collage: >50 proteins Classes: – Integral Proteins: Transmembrane proteins Penetrate hydrophobic core of membrane – Peripheral Loosely bound to surface Attached to cyto-skeleton or ECM (Extracellular matrix)

Function of Membrane Proteins

Functions of Membrane Proteins Transport (protein channels and pumps for active and passive transport) Enzymatic (catalysis) Signal transduction (substrates bind to protein surface  sends a signal within the cell) Intercellular Joining (gap junctions, etc.) Cell – to – cell recognition (oligosaccharides on proteins or lipids act as “name tags” for cells) ECM attachment – maintenance of cell shape

SelectiveSelective Permeability Selective General rule: like dissolves like – Non-polar/hydrophobic solutes dissolve in lipid – Ions and hydrophillic solutes dissolve in water Selective Permeability: some substances can pass more easily than others – CO 2, hydrocarbons, lipids, and O 2 are nonpolar (can pass membrane easily) – Water, glucose, sugars, charged ions (cannot pass easily)  so must use hydrophillic transport proteins to pass – Small molecules are more permeable than larger ones

Passive Transport Mvmt down [gradient] Spontaneous process –ΔG Types of Passive Transport: – Diffusion – Osmosis – Facilitated Diffusion

Diffusion Diffusion – molecules of any substance moves down [gradient] Diffusion

Osmosis – Osmosis (tonicity dependent) Osmosis Isotonic vs. hypotonic vs. hypertonic conditions Water always moves from hypotonic to hypertonic side

Facilitated Diffusion diffusion of solutes (ions) with help from channel proteins in the plasma membrane

Balancing Water Uptake Animals: cannot tolerate change in tonicity – Ex. Salt water fish vs. fresh water fish, vice versa – Some Freshwater protists keep from lysing due to contractile vacuoles

Balancing Water Uptake Plants: Cell walls help maintain water balance – Turgid Conditions Good! Turgid – Flacid Conditions cause plasmolysisplasmolysis – (lab 1E)

Active Transport Movement against [gradient] Nonspontaneous, + ΔG, Requires ATP Types: – Protein pumps – Cotransport – Exocytosis: Phagocytosis and Pinocytosis – Endocytosis – Receptor Mediated Endocytosis

Protein Pumps Ex: Sodium-Potassium PumpSodium-Potassium Ex: Pumping H + ions into lysosomes  electrochemical gradient set up due to high concentration of ions set up on one side of membrane compared to the other

Electrochemical Gradient

Co-transport Involves the active transport of a substance powered indirectly by an ATP powered pump H+ ATP H+

Exocytosis Fusing of vesicles to the plama membrane, thus releasing its contents

Endocytosis The engulfing of substances by pseudopods extensions of the plama membrane Three types: – Phagocytosis Phagocytosis – Pinocytosis Pinocytosis – Receptor Mediated Endocytosis Receptor