Microscope Skills, Magnification, and Cell Sizes Six Total Stations 1.Dissection Microscope (All organism) 2.Bacteria 3.The letter “e” 4.Paramecium 5.Bone Marrow 6.Butterfly Antenae

Chapter 5 Membrane Structure and Function Key Questions Why membranes are selectively permeable The role of phospholipids, proteins, and carbohydrates in membranes How water will move if a cell is placed in an isotonic, hypertonic, or hypotonic solution How electrochemical gradients are formed Homework Purchase or obtain from the library: (by the end of next week) –“A Short History of Nearly Everything” By Bill Bryson Read Pages in Chapter 5. Do now –What does it mean if something is permeable? –What does it mean if something is semi- permeable?

Extracellular Matrix Functions of the ECM: Support Adhesion Movement Regulation

The Extracellular Matrix (ECM) of Animal Cells The ECM is made up of glycoproteins such as… collagen, proteoglycans, and fibronectin ECM proteins bind to receptor proteins in the plasma membrane called integrins

Fig. 6-30a Collagen Fibronectin Plasma membrane Proteoglycan complex Integrins CYTOPLASM Micro- filaments EXTRACELLULAR FLUID

Fig. 6-30b Polysaccharide molecule Carbo- hydrates Core protein Proteoglycan molecule Proteoglycan complex

Intercellular Junctions Neighboring cells in tissues, organs, or organ systems often adhere, interact, and communicate through direct physical contact There are several types of intercellular junctions –Plasmodesmata –Tight junctions –Desmosomes –Gap junctions Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Tight Junctions, Desmosomes, and Gap Junctions in Animal Cells At tight junctions, membranes of neighboring cells are pressed together, preventing leakage of extracellular fluid Desmosomes (anchoring junctions) fasten cells together into strong sheets Gap junctions (communicating junctions) provide cytoplasmic channels between adjacent cells Animation: Tight Junctions Animation: Tight Junctions Animation: Desmosomes Animation: Desmosomes Animation: Gap Junctions Animation: Gap Junctions Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

7.1 Cellular membranes are fluid mosaics of lipids and proteins Plasma membrane is selectively permeable Phospholipids –Amphipathic molecules – hydrophobic and hydrophillic regions Integral proteins –Completely embedded in the membrane (hydrophobic core) –Some are transmembrane proteins that span the entire plasma membrane Peripheral proteins –Loosely bound to the membrane surface Carbohydrates –Attached to membrane and membrane bound proteins –Crucial in cell-cell recognition Glycolipids Glycoproteins

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

Does the plasma membrane move? (a) Movement of phospholipids Lateral movement (  10 7 times per second) Flip-flop (  once per month) How could temperature affect membrane movement? Freeze Fracture

Membrane Proteins and Their Functions Six major functions of membrane proteins: –Transport –Enzymatic activity –Signal transduction –Cell-cell recognition –Intercellular joining –Attachment to the cytoskeleton and extracellular matrix (ECM)

Fig. 7-9 (a) Transport ATP (b) Enzymatic activity Enzymes (c) Signal transduction Signal transduction Signaling molecule Receptor (d) Cell-cell recognition Glyco- protein (e) Intercellular joining (f) Attachment to the cytoskeleton and extracellular matrix (ECM)

The Role of Membrane Carbohydrates in Cell-Cell Recognition Cells recognize each other by binding to surface molecules, often carbohydrates, on the plasma membrane –Glycolipids –Glycoproteins (more common) These Carbohydrates –vary among species, individuals, and even cell types in an individual Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig ER 1 Transmembrane glycoproteins Secretory protein Glycolipid 2 Golgi apparatus Vesicle 3 4 Secreted protein Transmembrane glycoprotein Plasma membrane: Cytoplasmic face Extracellular face Membrane glycolipid Membranes have distinct inside and outside faces Membrane synthesis

Concept 7.2: Membrane structure results in selective permeability Hydrophobic (nonpolar) molecules, such as hydrocarbons, can dissolve in the lipid bilayer and pass through the membrane rapidly Polar molecules (& ionic molecules), such as sugars, do not cross the membrane easily

Transport Proteins Transport proteins –allow passage of hydrophilic substances across the membrane Some transport proteins, called channel proteins, have a hydrophilic channel that certain molecules or ions can use as a tunnel Channel proteins called aquaporins facilitate the passage of waterChannel proteins called aquaporins facilitate the passage of water

Concept 7.3: Passive transport is diffusion of a substance across a membrane with no energy investment Diffusion is the tendency for molecules to spread out evenly into the available space Substances diffuse down their concentration gradient – the difference in concentration of a substance from one area to another –Although each molecule moves randomly, diffusion of a population of molecules may exhibit a net movement in one direction –At dynamic equilibrium as many molecules cross one way as cross in the other direction Animation: Membrane Selectivity Animation: Membrane Selectivity Animation: Diffusion Animation: Diffusion Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

(Start)Effects of Osmosis on Water Balance Osmosis is the diffusion of water across a selectively permeable membrane Tonicity is the ability of a solution to cause a cell to gain or lose water Isotonic solution: Solute concentration is the same as that inside the cell; no net water movement across the plasma membrane Hypertonic solution: Solute concentration is greater than that inside the cell; cell loses water Hypotonic solution: Solute concentration is less than that inside the cell; cell gains water Osmoregulation, the control of water balance, is a necessary adaptation for life in such environments

Fig Hypotonic solution (a ) Animal cell (b ) Plant cell H2OH2O Lysed H2OH2O Turgid (normal) H2OH2O H2OH2O H2OH2O H2OH2O Normal Isotonic solution Flaccid H2OH2O H2OH2O Shriveled Plasmolyzed Hypertonic solution

Water Balance of Cells with Walls Cell walls help maintain water balance Turgid - good Flaccid - bad plasmolysis –In a hypertonic environment, plant cells lose water; eventually, the membrane pulls away from the wall, a usually lethal effect Video: Plasmolysis Video: Plasmolysis

Facilitated Diffusion: Passive Transport Aided by Proteins In facilitated diffusion, transport proteins speed the passive movement of molecules across the plasma membrane Channel proteins include –Aquaporins, for facilitated diffusion of water –Ion channels that open or close in response to a stimulus (gated channels) EXTRACELLULAR FLUID Channel protein (a) A channel protein Solute CYTOPLASM Solute Carrier protein (b) A carrier protein

Concept 7.4: Active transport uses energy to move solutes against their gradients Some transport proteins can move solutes against their concentration gradients Active transport moves substances against their concentration gradient –Active transport requires energy, usually in the form of ATP –Active transport is performed by specific proteins embedded in the membranes Animation: Active Transport Animation: Active Transport

Sodium-Potassium pump Active transport allows cells to maintain concentration gradients that differ from their surroundings The sodium-potassium pump is one type of active transport system

2 EXTRACELLULAR FLUID [Na + ] high [K + ] low [Na + ] low [K + ] high Na + CYTOPLASM ATP ADP P Na + P 3 K+K+ K+K+ 6 K+K+ K+K+ 5 4 K+K+ K+K+ P P 1 Fig Video of NA – K pump

Fig Passive transport Diffusion Facilitated diffusion Active transport ATP

Big Idea!!! Membrane potential is the voltage difference across a membrane –Voltage is created by differences in the distribution of positive and negative ions electrochemical gradient –A chemical force (the ion’s concentration gradient) –An electrical force (the effect of the membrane potential on the ion’s movement) –electrogenic pump –proton pump

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

Cotransport: Coupled Transport by a Membrane Protein Cotransport occurs –when active transport of a solute indirectly drives transport of another solute Plants commonly use the gradient of hydrogen ions generated by proton pumps to drive active transport of nutrients into the cell

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

Concept 7.5: Bulk transport across the plasma membrane occurs by exocytosis and endocytosis Exocytosis – fusion of vesicle to membrane for release Endocytosis - the cell takes in macromolecules by forming vesicles from the plasma membrane Endocytosis is a reversal of exocytosis, involving different proteins There are three types of endocytosis: – Phagocytosis (“cellular eating”) – Pinocytosis (“cellular drinking”) – Receptor-mediated endocytosis

Exocytosis/Endocytosis Exocytosis – fusion of vesicle to membrane for release Endocytosis - the cell takes in macromolecules by forming vesicles from the plasma membrane Endocytosis is a reversal of exocytosis, involving different proteins There are three types of endocytosis: –Phagocytosis (“cellular eating”) –Pinocytosis (“cellular drinking”) –Receptor-mediated endocytosis Animation: Exocytosis and Endocytosis Introduction Animation: Exocytosis and Endocytosis Introduction

Fig. 7-20a PHAGOCYTOSIS CYTOPLASM EXTRACELLULAR FLUID Pseudopodium “Food” or other particle Food vacuole Food vacuole Bacterium An amoeba engulfing a bacterium via phagocytosis (TEM) Pseudopodium of amoeba 1 µm

Fig. 7-20b PINOCYTOSIS Plasma membrane Vesicle 0.5 µm Pinocytosis vesicles forming (arrows) in a cell lining a small blood vessel (TEM)

In receptor-mediated endocytosis, binding of ligands to receptors triggers vesicle formation A ligand is any molecule that binds specifically to a receptor site of another molecule Animation: Receptor-Mediated Endocytosis Animation: Receptor-Mediated Endocytosis

Fig. 7-20c RECEPTOR-MEDIATED ENDOCYTOSIS Receptor Coat protein Coated pit Ligand Coat protein Plasma membrane 0.25 µm Coated vesicle A coated pit and a coated vesicle formed during receptor- mediated endocytosis (TEMs)

Fig EXTRACELLULAR FLUID [Na + ] high [K + ] low Na + [Na + ] low [K + ] high CYTOPLASM Cytoplasmic Na + binds to the sodium-potassium pump. 1

Na + binding stimulates phosphorylation by ATP. Fig Na + ATP P ADP 2

Fig Phosphorylation causes the protein to change its shape. Na + is expelled to the outside. Na + P 3

Fig K + binds on the extracellular side and triggers release of the phosphate group. P P K+K+ K+K+ 4

Fig Loss of the phosphate restores the protein’s original shape. K+K+ K+K+ 5

Fig K + is released, and the cycle repeats. K+K+ K+K+ 6