CELL MEMBRANE STRUCTURE & FUNCTIONS PASSIVE DIFFUSION, OSMOSIS, FACILITATED DIFFUSION AND ACTIVE TRANSPORT

WATER Hydrophilic head Hydrophobic tail WATER

Phospholipid bilayer Hydrophobic regions of protein Hydrophilic regions of protein

TECHNIQUE RESULTS Extracellular layer Proteins Inside of extracellular layer Knife Plasma membrane Cytoplasmic layer Inside of cytoplasmic layer

Lateral movement (~107 times per second) Flip-flop (~ once per month) (a) Movement of phospholipids Fluid Viscous Unsaturated hydrocarbon tails with kinks Saturated hydro- carbon tails (b) Membrane fluidity Cholesterol (c) Cholesterol within the animal cell membrane

Cell Membrane Structures Recognition Factors Antenna that capture required solutes/hormnones Amphipathic nature of the phospholipids and its consequences Integral Proteins

Fibers of extracellular matrix (ECM) Glyco- Carbohydrate protein Glycolipid EXTRACELLULAR SIDE OF MEMBRANE Cholesterol Microfilaments of cytoskeleton Peripheral proteins Integral protein CYTOPLASMIC SIDE OF MEMBRANE

(b) Enzymatic activity (c) Signal transduction MEMBRANE PROTEINS Signaling molecule Enzymes Receptor ATP Signal transduction (a) Transport (b) Enzymatic activity (c) Signal transduction Glyco- protein (d) Cell-cell recognition (e) Intercellular joining (f) Attachment to the cytoskeleton and extracellular matrix (ECM)

EXTRACELLULAR SIDE N-terminus C-terminus CYTOPLASMIC SIDE  Helix

Importance 1. Acquire molecules & Ions 2 Importance 1. Acquire molecules & Ions 2.Transport into and out of cell through membrane 3.Transport WITHIN the cell ER 1 Transmembrane glycoproteins Secretory protein Glycolipid Golgi apparatus 2 Vesicle 3 Plasma membrane: Cytoplasmic face 4 Extracellular face Transmembrane glycoprotein Secreted protein Membrane glycolipid

Cell Membrane Function Problems and Solutions 1. Relative concentrations a. Passive Transport b. Active Transport 2. Lipid bilayers are impermeable to most essential molecules and ions a. permeable to:

Cell membrane function, con’t b. impermeable to: -

SIMPLE DIFFUSION REQUIRES A CONCENTRATION GRADIENT FACILITATED DIFFUSION REQUIRES A CONCENTRATION GRADIENT AND A PROTEIN TRANSPORTER

Molecules of dye Membrane (cross section) WATER Net diffusion Net diffusion Equilibrium (a) Diffusion of one solute

Relate to Lab: Glucose, Starch. NaCl, Proitein Net diffusion Net diffusion Equilibrium Net diffusion Net diffusion Equilibrium (b) Diffusion of two solutes

Channel protein Solute (a) A channel protein Solute Carrier protein EXTRACELLULAR FLUID Channel protein Solute CYTOPLASM (a) A channel protein Solute Carrier protein (b) A carrier protein

REQUIRES A PROTEIN TRANSPORTER AND ATP ENERGY ACTIVE TRANSPORT REQUIRES A PROTEIN TRANSPORTER AND ATP ENERGY

Active transport: ATP

1 2 3 6 5 4 EXTRACELLULAR FLUID [Na+] high Na+ [K+] low Na+ Na+ Na+ [Na+] low ATP Na+ P P CYTOPLASM [K+] high ADP 1 2 3 K+ K+ K+ K+ K+ P K+ P 6 5 4

– EXTRACELLULAR FLUID + ATP – + H+ H+ Proton pump H+ – + H+ H+ H+ – + CYTOPLASM H+ – +

– + H+ ATP H+ – + H+ H+ – + H+ H+ – + H+ H+ – + – + Diffusion of H+ Proton pump H+ H+ – + H+ H+ – + H+ Diffusion of H+ Sucrose-H+ cotransporter H+ – Sucrose + – + Sucrose

Facilitated diffusion REVIEW Passive transport Active transport ATP Diffusion Facilitated diffusion

Osmosis Passive Diffusion of Water Dissociation of ions in solution Aquaporins Osmotic concentration Free Energy Water Potential

Tonicity of cell IN COMPARISON TO the environment: The cell is ________in comparison to the environment. Hence, water will move from _____________________ to ____________. The results: Cell Interior: Less than 1% solute ENVIRONMENT 99% water

cell cell Hypotonic solution Isotonic solution Hypertonic solution H2O (a) Animal cell Lysed Normal Shriveled H2O H2O H2O H2O (b) Plant cell Turgid (normal) Flaccid Plasmolyzed

Cell with less than 1 % solute Cell with less than 1 % SOLUTE (freshwater cell with more than 99% water) Cell with less than 1 % solute Environment with greater than 10% SOLUTE (less than 90 % water) Cell Environment Osmotic or Solute Potential - Free Energy Osmotic Potential Osmotic Pressure Water Potential Ψ

Environment: 0.01 M sucrose 0.01 M glucose 0.01 M fructose “Cell” 0.03 M sucrose 0.02 M glucose

Lower concentration of solute (sugar) Higher concentration of sugar Same concentration of sugar H2O Selectively permeable membrane Osmosis

Additional transport Mechanisms Bulk Transport Endocytosis Phagocytosis Pinocytosis Receptor-mediated endocytosis

PHAGOCYTOSIS CYTOPLASM 1 µm EXTRACELLULAR FLUID Pseudopodium of amoeba “Food” or other particle Bacterium Food vacuole Food vacuole An amoeba engulfing a bacterium via phagocytosis (TEM)

PINOCYTOSIS Plasma membrane Vesicle 0.5 µm Pinocytosis vesicles forming (arrows) in a cell lining a small blood vessel (TEM) Vesicle

Coat protein Receptor Coated vesicle Coated pit Ligand A coated pit RECEPTOR-MEDIATED ENDOCYTOSIS Coat protein Receptor Coated vesicle Coated pit Ligand A coated pit and a coated vesicle formed during receptor- mediated endocytosis (TEMs) Coat protein Plasma membrane 0.25 µm