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

Membrane proteins Mixed proteins after 1 hour Mouse cell Human cell Hybrid cell

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

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

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)

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

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

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

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

(a) A contractile vacuole fills with fluid that enters from Filling vacuole (a) A contractile vacuole fills with fluid that enters from a system of canals radiating throughout the cytoplasm. Contracting vacuole (b) When full, the vacuole and canals contract, expelling fluid from the cell.

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

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

Passive transport Active transport ATP Diffusion Facilitated diffusion

– 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

PHAGOCYTOSIS EXTRACELLULAR FLUID CYTOPLASM 1 µm Pseudopodium Pseudopodium of amoeba “Food”or other particle Bacterium Food vacuole Food vacuole An amoeba engulfing a bacterium via phagocytosis (TEM) PINOCYTOSIS 0.5 µm Plasma membrane Pinocytosis vesicles forming (arrows) in a cell lining a small blood vessel (TEM) Vesicle 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