8.(i) Cell-cell Interactions- Key ConceptsSlide 2Slide 3Biology Is Studied at Many Levels of OrganizationSlide 5The Structure and Function of an Extracellular LayerThe Primary Plant Cell WallCell-Cell AttachmentsSlide 9The Extracellular Matrix in AnimalsSlide 11The ECM and Cytoskeleton Are Directly LinkedSlide 13Slide 14Slide 15Slide 16How Do Adjacent Cells Connect and Communicate?Connections between Animal CellsTight JunctionsSlide 20DesmosomesSelective AdhesionThe Molecular Basis of Selective AdhesionSlide 24Slide 25Cell Communication via Cell-Cell GapsSlide 27Summary of Eukaryotic Cell-Cell Attachments© 2011 Pearson Education, Inc.8.(i) Cell-cell Interactions- Key ConceptsHow cells in multi cellular organisms stick together (i) and communicate (ii)?Extracellular material (ECM) strengthens cells and helps bind them together.Cell-cell connections help adjacent cells adhere. Cell-cell gaps allow adjacent cells to communicate (cell adhesion and cell communication)© 2011 Pearson Education, Inc.Intercellular signals are responsible for creating an integrated whole from many thousands of independent parts.In target cells, intercellular signals are received, processed, responded to, and deactivated. If the signal is received at the cell surface, the processing step involves production of an intracellular signal.8. (ii) Cell-cell Interactions- Cell communication:For a tissue or an organ to function as a unit, there must be cell-cell communication among the cells within a tissue or organ (cells need to work together)© 2011 Pearson Education, Inc.•All living things are made of similar sub-components, which are evolved to have related/different functions in different life forms (Structure and Function)•All living things rely on chemical reactions to process matter and acquire energy for cellular functions. Some energy transformations are nearly universal while some are restricted to certain species (Pathways and Transformations of Energy and Matter)•DNA is the instruction code or the blue print for life; how it is used and exchanged within and among life forms is the basis of life (Information Flow, Exchange and Storage)•Organisms and their cellular components have changed over time (biodiversity) through both selection (mutations) and random evolutionary processes (Evolution)•Life is predictably interconnected - from cells within an organism to interactions between global communities (Systems)© 2011 Pearson Education, Inc.Biology Is Studied at Many Levels of Organization© 2011 Pearson Education, Inc.•For a tissue or an organ to function as a unit, there must be cell-cell communication among the cells within a tissue or organ (cells need to work together)© 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.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.Some cells secrete a secondary cell wall inside the primary cell wall. Secondary cell wall structure correlates with the specific cell’s function.© 2011 Pearson Education, Inc.Cell-Cell Attachments •The structures that hold cells together vary among multicellular organisms.Connections between Plant Cells:The extracellular space between adjacent plant cells comprises three layers.Middle  helps to glueAdjacent cells.© 2011 Pearson Education, Inc.What is the function of the middle lamella in plant cells? It allows adjacent cells to adhere to one another.© 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.•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• 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.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.Integrins are integral membrane proteins. They are often attached to cytoskeletal proteins and proteins in the extracellular matrix.Collagen: (in animals)© 2011 Pearson Education, Inc.An experiment on the open seas:James Lind was a Scottish sea captain on the ship MSS Salisbury, headed towards Plymouth, England.He had 12 men on board who were suffering from  bleeding gum, weak knees, fatigue….He divided sick men in to 6 groups of 2, all were given the basic diet at meals.Each group was given a different supplement each day  Apple cider, vinegar, mixture of herbs, quart of sea water, sugar, 2 orangesThe results were striking; within 6 days, the last group who ate oranges were ready for duty?????© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.Plant ECM is primarily carbohydrate in nature, whereas animal ECM is mainly proteins.© 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.In multicellular organisms, Cells are connected.© 2011 Pearson Education,