Membranes Structure and Function Chapter 5 Copyright © McGraw-Hill Companies Permission required for reproduction or display Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Raven - Johnson - Biology: 6th Ed Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Plasma Membrane Consists of: * nonpolar lipid bilayer impedes the passage of water soluble substances * degree of fluidity is determined by degree of alignment of phospholipids. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Plasma Membrane Consists of: 1. Lipid bilayer Phospholipids have a glycerol backbone with two attached fatty acid chains. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Examples: small non-charged molecules, CO2, O2, glycerol, and alcohol. Plasma Membrane is: Selectively Permeable – meaning that it allows substances to cross the cell membrane passively Examples: small non-charged molecules, CO2, O2, glycerol, and alcohol. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

* allows for passage of substances 2. Proteins * allows for passage of substances Mosaic of proteins float in fluid lipid bilayer. Transmembrane Proteins Network of Interior Proteins Cell Surface markers Copyright © McGraw-Hill Companies Permission required for reproduction or display Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Raven - Johnson - Biology: 6th Ed Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Cell Membrane Proteins Six kinds of Membrane Proteins Transporters – channels or carriers Enzymes – rxns. occur in interior of cell Cell Surface Receptors – detect chem. messengers Cell Surface Identity Markers – id cell types Cell Adhesion Proteins – connect cells Cytoskeleton Attachments Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Raven - Johnson - Biology: 6th Ed Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

How are proteins anchored on the cell membrane? Proteins contain polar and nonpolar regions that allow them to be anchored. Anchoring Proteins - Attached to membrane surface. Transmembrane Proteins Anchor proteins Channels and Carriers Pores Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Passive Transport: Diffusion Facilitated Diffusion Osmosis Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Continues until equilibrium reached. Diffusion Random movement of substances from regions of high concentration to regions of lower concentration.(with the [gradient]) Continues until equilibrium reached. Copyright © McGraw-Hill Companies Permission required for reproduction or display Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Facilitated Diffusion Each polar molecule transported across the plasma membrane has its own type of channel protein. Selective permeability Ions move across membrane in ion channels. Direction of movement determined by relative concentrations and voltage across membrane. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Facilitated Diffusion Carrier proteins facilitate movement of solutes across membrane by physically binding to them on one side of the membrane and releasing them on the other. Driven by concentration gradients. Copyright © McGraw-Hill Companies Permission required for reproduction or display Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Facilitated Diffusion Three Essential Characteristics: Specific Passive Saturates Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Most solutes are not lipid soluble and thus cannot cross membrane. Osmosis In an aqueous solution, both water and solutes diffuse down a concentration gradient. Most solutes are not lipid soluble and thus cannot cross membrane. Water flows through aquaporins in membrane. Net movement of water across a membrane is termed osmosis. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Osmotic Concentration - Concentration of all solutes in a solution. Osmosis Osmotic Concentration - Concentration of all solutes in a solution. Hyperosmotic (Hypertonic)- Solution with higher concentration of solutes. Hypoosmotic (Hypotonic)- Solution with lower concentration of solutes. Isosmotic (Isotonic)- Osmotic concentrations of both solutions are the same. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Osmosis Copyright © McGraw-Hill Companies Permission required for reproduction or display Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Fig. 6.15 Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Mechanisms For Maintaining Osmotic Balance Extrusion Osmotic Pressure Hydrostatic Pressure is caused by cytoplasm pushing out against cell membrane. Osmotic Pressure is the pressure necessary to stop osmotic movement of water across a membrane. Mechanisms For Maintaining Osmotic Balance Extrusion Isomotic Solutions Turgor Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Fig. 6.16 Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Phagocytosis - “Cell eating” Particulate form – discrete particles. Bulk Transport: 1. Endocytosis - Plasma membrane extends outward and envelops food particles. Phagocytosis - “Cell eating” Particulate form – discrete particles. Copyright © McGraw-Hill Companies Permission required for reproduction or display Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Pinocytosis - “Cell drinking” Liquid form. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Receptor-Mediated Endocytosis - Molecules first bind to specific receptors on plasma membrane before being engulfed Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

2 Exocytosis - Discharge of material from vesicles at cell surface; mechanism for secreting many hormones, digestive enzymes, etc. Copyright © McGraw-Hill Companies Permission required for reproduction or display Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Requires input of energy. Active Transport: Movement of substances across a membrane against their concentration gradients. Requires input of energy. Enables cell to take up additional molecules of a substance already present in its cytoplasm in concentrations higher than in extracellular fluid. Example: Sodium-Potassium Pump moves 3 Na+ out and 2 K+ in Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Raven - Johnson - Biology: 6th Ed Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Raven - Johnson - Biology: 6th Ed Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Coupled Transport Active transport that moves molecules coupled with sodium ions or protons down their concentration gradients (Cotransport). Establish the down gradient. Sodium-potassium or proton pump. Trasverse the upgradient. Cotransport Symport – ex. Na+ and sugar/a.a. Countertransport Antiport – ex. Na+ inward and Ca++ outward Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Raven - Johnson - Biology: 6th Ed Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Raven - Johnson - Biology: 6th Ed Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Intercellular Adhesion Cell clusters form long-lasting or permanent connections with each other (cell junctions). The nature of the connections determines what the tissue is like. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Raven - Johnson - Biology: 6th Ed Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Tight junctions connect plasma membranes of adjacent cells in a sheet. Prevent small molecules from leaking between cells and through the sheet. Effectively segregate proteins on opposite sides of the sheet. Fuse like a zipper Ex. Prevent digestive enzymes from seeping into blood Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Raven - Johnson - Biology: 6th Ed Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Hemidesmosomes - Anchor epithelial cells to basement membrane. Anchoring Junctions Anchoring junctions mechanically attach cytoskeleton of one cell to cytoskeleton of other cells, or to the extracellular matrix. Desmosomes - Connect cytoskeletons of adjacent cells; prevent cells subjected to mechanical stress from pulling apart; they are buttonlike thickenings of plasma membrane Hemidesmosomes - Anchor epithelial cells to basement membrane. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Desmosomes Copyright © McGraw-Hill Companies Permission required for reproduction or display Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Anchoring Junctions Cadherins - Connect actin frameworks of cells in cadherin-mediated junctions. Adherens - Connect actin filaments of one cell with those of neighboring cells or with extracellular matrix. Integrin proteins Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Communicating Junctions Communication junctions pass chemical signals directly from one cell to adjacent cells. Establish direct physical connections. Animals Gap Junctions Connexons. Plants Plasmodesmata Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Copyright © McGraw-Hill Companies Permission required for reproduction or display Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

The End Copyright © McGraw-Hill Companies Permission required for reproduction or display Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies