Chapter 8 – Cell-cell interactionsReview of Plasma Membrane Structure and FunctionThe Structure and Function of an Extracellular LayerSlide 4The Primary Plant Cell WallSlide 6The Secondary Plant Cell WallThe Extracellular Matrix in AnimalsExtracellular Matrix Structure and FunctionSlide 10The ECM and Cytoskeleton Are Directly LinkedSlide 12How Do Adjacent Cells Connect and Communicate?Slide 14Cell-Cell AttachmentsConnections between Plant CellsSlide 17Connections between Animal CellsTight JunctionsSlide 20DesmosomesSlide 22Selective AdhesionThe Molecular Basis of Selective AdhesionCell Communication via Cell-Cell GapsSlide 26Summary of Eukaryotic Cell-Cell AttachmentsSlide 28How Do Distant Cells Communicate?Hormones Are Long-Distance MessengersHormones Vary Widely in Effect and StructureSlide 32Steps of Cell-Cell SignalingStep 1: Signal ReceptionSignal ReceptorsStep 2: Signal ProcessingSignal Processing in Lipid-Soluble HormonesSlide 38Signal Processing in Lipid-Insoluble HormonesSlide 40Signal TransductionG ProteinsG Proteins and Signal TransductionSlide 44Second MessengersEnzyme-Linked ReceptorsReceptor Tyrosine Kinases and Signal TransductionSlide 48Slide 49Results of Signal ProcessingStep 3: Signal ResponseStep 4: Signal DeactivationSummary of Hormonal SignalingInteractions between Signaling PathwaysCross-Talk, Interactions between Signaling PathwaysQuorum Sensing in BacteriaResponses to Signaling in BacteriaKey Concepts© 2011 Pearson Education, Inc.Chapter 8 – Cell-cell interactions© 2011 Pearson Education, Inc.Review of Plasma Membrane Structure and Function•The plasma membrane is made up of a phospholipid bilayer with many interspersed proteins. –Proteins may be integral or peripheral.•The primary function of the plasma membrane is to create an environment inside the cell that is different from conditions outside.–The selective permeability of the membrane controls the flow of materials into and out of the cell.© 2011 Pearson Education, Inc.The Structure and Function of an Extracellular LayerStructure•Most cells possess a protective layer or wall that forms just beyond the membrane. This layer generally consists of a “fiber composite” – a cross-linked network of long filaments surrounded by a stiff ground substance. Function•The rods or filaments protect against tension, and the ground substance protects against compression.© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.The Primary Plant Cell Wall•When new plant cells form, they secrete a fiber composite called a primary cell wall.–This wall is composed of long strands of cellulose bundled into microfibrils that form a crisscrossed network. –The network is filled with hydrophilic gelatinous polysaccharides such as pectin, which keep the cell wall moist.•The primary cell wall defines the shape of the plant cell and counteracts the turgor pressure it experiences.© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.The Secondary Plant Cell Wall•Some cells secrete a secondary cell wall inside the primary cell wall.–Secondary cell wall structure correlates with the specific cell’s function.•In cells that form wood, the secondary cell wall contains lignin.© 2011 Pearson Education, Inc.The Extracellular Matrix in Animals•Most animal cells secrete a fiber composite called the extracellular matrix (ECM).Like the extracellular materials found in other organisms, one of the ECM’s most important functions is structural support. •The amount and composition of the ECM vary depending upon the cell type.© 2011 Pearson Education, Inc.Extracellular Matrix Structure and Function•The ECM consists of a ground substance formed of gelatinous polysaccharide and a network of protein fibers.–The most common ECM protein fiber is collagen, which is more elastic than cellulose and forms a flexible extracellular layer.•In addition to structural support, the ECM also helps cells stick together, and forms protein-protein attachments that link the ECM directly to the cell’s cytoskeleton.© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.The ECM and Cytoskeleton Are Directly Linked•The ECM is strengthened by connections to transmembrane proteins.•Actin protein filaments in the cytoskeleton bind to transmembrane integrin proteins. Integrins bind to ECM proteins such as fibronectins, which then bind to collagen.•Direct linkage between the cytoskeleton and ECM keeps individual cells in place and helps adjacent cells adhere to each other.–Breakdown can lead to metastasis of cancerous cells.© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.How Do Adjacent Cells Connect and Communicate?•Unicellular organisms do not usually connect to one another; physical connections between cells are the basis of multicellularity.•Cells of multicellular organisms adhere to one another and have specific, distinct structures and functions.–Groups of similar cells performing similar functions comprise tissues.© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.Cell-Cell Attachments •The structures that hold cells together vary among multicellular organisms.© 2011 Pearson Education, Inc.Connections between Plant Cells•The extracellular space between adjacent plant cells comprises three layers.•Plant cells are glued together by the middle lamella, which is continuous with the adjacent plant cells’ primary cell walls.–The middle lamella is comprised of gelatinous pectins.© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.Connections between Animal Cells•A middle-lamella-like layer, made of gelatinous polysaccharides, exists between cells in many animal tissues. –The polysaccharide glue may be reinforced by cable-like proteins that span the ECM to connect adjacent cells. •Epithelial tissue is composed of sheets of cells that cover organs and line body cavities. –Many types of structures connect neighboring epithelial cells, including tight junctions and desmosomes.© 2011 Pearson Education, Inc.Tight Junctions•Tight junctions are composed of specialized proteins in the plasma membranes of adjacent animal cells. –These proteins line up and bind to each other, stitching the two cells together to form a watertight seal between the two plasma membranes.•Tight junctions are usually found between cells in tissues that form a barrier, such as the tissue lining the stomach or bladder.•Tight junctions are dynamic and