What do these have in common? HIV infection Transplanted organs Communication between neurons Drug addiction Cystic fibrosis hypercholesteremia

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings selectively permeable hold teams of enzymes Membranes organize the chemical activities of cells Cytoplasm   Figure 5.10

Plasma membrane Contact between cell and environment Keeps useful materials inside and harmful stuff outside Allows transport, communication in both directions Anchors energy-converting enzymes

Plasma membrane components  Phospholipid bilayer  Cholesterol  Proteins  Glycocalyx

polar head nonpolar tails P– Phospholipid bilayer hydrophobic moleculeshydrophilic molecules cytosol

THE PLASMA MEMBRANE phospholipids cholesterol cytoskeleton peripheral protein integral protein Cholesterol blocks some small molecules, adds fluidity

Membrane Proteins –span entire membrane or lie on either side –Purposes Structural Support Recognition Communication Transport

Glycocalyx –Composed of sugars protruding from lipids and proteins –Functions Binding sites for proteins Lubricate cells. Stick cells down.

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Many membrane proteins are enzymes Figure 5.13 Some proteins function as receptors for chemical messages from other cells –The binding of a messenger to a receptor may trigger signal transduction Enzyme activitySignal transduction Messenger molecule Receptor Activated molecule

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The plasma membrane of an animal cell Fibers of the extracellular matrix Figure 5.12 Glycoprotein Carbohydrate (of glycoprotein) Microfilaments of the cytoskeleton Phospholipid Cholesterol Proteins CYTOPLASM Glycolipid

Diffusion and Gradients –Diffusion = movement of molecules from region of higher to lower concentration. –Osmosis = diffusion of water across a membrane

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings In passive transport, substances diffuse through membranes without work by the cell EQUILIBRIUM Molecule of dye Figure 5.14A & B Membrane EQUILIBRIUM

free water molecule: can fit through pore bound water molecules clustered around sugar: cannot fit through pore pore sugar H2OH2O bag bursts selectively permeable membrane water molecule pure water sugar molecule (a) selectively permeable membrane (b)

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings water travels from an area of higher concentration to an area of lower water concentration Osmosis = diffusion of water across a membrane Hypotonic solution Figure 5.15 Solute molecule HYPOTONIC SOLUTION Hypertonic solution Selectively permeable membrane HYPERTONIC SOLUTION Selectively permeable membrane NET FLOW OF WATER Solute molecule with cluster of water molecules Water molecule

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Osmosis causes cells to shrink in a hypertonic solution and swell in a hypotonic solution Water balance between cells and their surroundings is crucial to organisms osmoregulation = control of water balance

isotonic solutionhypertonic solutionhypotonic solution 10 microns equal movement of water into and out of cells net water movement out of cells net water movement into cells

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Small nonpolar molecules - simple diffusion Many molecules pass through protein pores by facilitated diffusion Passive transport = diffusion across membranes Figure 5.17 Solute molecule Transport protein

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings transport proteins needed against a concentration gradient requires energy (ATP) Active transport

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Active transport in two solutes across a membrane Na+/K+ pump Protein shape change Figure 5.18 Transport protein 1 FLUID OUTSIDE CELL First solute First solute, inside cell, binds to protein Phosphorylated transport protein 2 ATP transfers phosphate to protein 3 Protein releases solute outside cell 4 Second solute binds to protein Second solute 5 Phosphate detaches from protein 6 Protein releases second solute into cell

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings exocytosis = vesicle fuses with the membrane and expels its contents Exocytosis and endocytosis transport large molecules Figure 5.19A FLUID OUTSIDE CELL CYTOPLASM

b

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings –or the membrane may fold inward, trapping material from the outside (endocytosis) Figure 5.19B

food particle particle enclosed in vesicle phagocytosis 132 Phagocytosis, “cell eating” —How the human immune system ingests whole bacteria or one-celled creatures eat.

(extracellular fluid) (cytoplasm) vesicle containing extracellular fluid pinocytosis 2

extracellular fluid plasma membrane vesiclecytosol receptors captured molecules coated pit vesicle bacteriumpseudopodium vesicle

Receptor-mediated endocytosis

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Cholesterol can accumulate in the blood if membranes lack cholesterol receptors Figure 5.20 LDL PARTICLE Phospholipid outer layer Protein Cholesterol Plasma membrane CYTOPLASM Receptor protein Vesicle

What do these have in common? HIV infection Transplanted organs Communication between neurons Drug addiction Cystic fibrosis hypercholesteremia