Chapter 7 and 11 Membrane “Strunction”Strunction

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:Integral Proteins Transmembrane proteins Penetrate hydrophobic core of membrane –Peripheral Loosely bound to surface Attached to cyto-skeleton or ECM (Extracellular matrix)

Review: Review: What organelles are responsible for creating membrane proteins?

Selective Permeability 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 lipid membrane core easily) –Water, glucose, sugars, charged ions (cannot pass lipid core easily)  so must use hydrophillic transport proteins to pass (ex. Aquaporins) Aquaporins –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]

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

Balancing Water Uptake Animals: cannot tolerate change in tonicity –Ex. Salt water fish vs. fresh water fish, vice versa –Some Freshwater protists prevent 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 review)

Function of Membrane Proteins protein channels for passive transportpassive transport protein pumps for active transport Catalysis of Chemical Reactions at the Membrane Surface substrates bind to protein surface  sends a signal within the cell to start a chemical chain reaction or cell responsesends a signal oligosaccharides on proteins or lipids act as “name tags” for cells. Ex. Gap Junctions, Tight Junctions, etc. Maintenance of Cell Shape End of Slide Show

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

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

Active Transport generates an electrochemical gradient: charge difference (disequilibrium) between both sides of the membrane

Protein Pumps Ex 1: Sodium-Potassium PumpSodium-Potassium (take notes about the function of Na/K pump from the video) Sodium-Potassium Pump 3-D overview3-D overview Ex 2: Pumping H + ions into lysosome to create acidic env’t

Co-transport Involves the transport of a substance against a concentration gradient powered indirectly by an ATP powered pump H+ ATP H+ ADP + Pi

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

Endocytosis Back to Function of Membrane Proteins The engulfing of substances by pseudopods extensions of the plasma membrane Three types: –Phagocytosis (cell eating – lg. particles engulfed)Phagocytosis –Pinocytosis (cell drinking – sm. ions and liquids engulfed) –Receptor Mediated Endocytosis (use of surface proteins to engulf a specific substrate)Receptor

Signal Transduction 3 Stages of Signal Transduction 1)Reception: A ligand (analogous to a substrate) binds to receptor protein. Receptor proteins can be on the cell surface, but not always. Receptor protein changes shape 2)Transduction: Amplifies and sends the signal through chemical relay 3)Cell Response: Specific response is triggered

Examples of Signal Transduction Why is this hormone-receptor protein not found on the surface of the plasma membrane? Steroids and Hormones are types of lipids, which can pass through phospholipid membranes easily. Back to Function of Membrane Proteins