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Cell Surfaces and Junctions Presentation to environment Defense mechanisms Maintain Structure Allow communication between cells Plant Cell Walls Flexible primary wall is later reinforced by more rigid secondary walls Area between cells is filled with Middle lamella Contains pectin which is a sticky gelatinous molecules Plasmodesmata are channels between cells that allow cytoplasm exchange Fig. 6-28 Secondary cell wall Primary cell wall Middle lamella 1 µm Central vacuole Cytosol Plasma membrane Plant cell walls Plasmodesmata Extracellular matrix Many types of glycoproteins Proteoglycans are more carbohydrate than protein Form branched complexes Fibronectins act as docking site Bound to Integrins Integrins span membrane and are bound to cytoskeleton Fig. 6-30 Collagen Proteoglycan complex EXTRACELLULAR FLUID Polysaccharide molecule Carbohydrates Fibronectin Core protein Integrins Proteoglycan molecule Plasma membrane Proteoglycan complex Microfilaments CYTOPLASM Role of ECM Gives tissue stability by linking areas of cells together Allows communication between cells Like cargo net Fibronectin and integrins are involved in signal sending and receiving ECM is essential in development Provide landmarks for extending structures Neurons and vascular tissue Intercellular junctions Tight junctions connect cells together and block of “seepage” of extracellular fluids Desmosomes anchor adjacent cells together structurally Linked to Intermediate filaments Gap junctions allow molecules to pass from cell to cell Comparable to plasmodesmata in plants Fig. 6-32 Tight junction Tight junctions prevent fluid from moving across a layer of cells 0.5 µm Tight junction Intermediate filaments Desmosome Gap junctions Space between cells Plasma membranes of adjacent cells Desmosome 1 µm Extracellular matrix Gap junction 0.1 µm Overview of cell revisited Emergent properties Something extra that makes the whole greater than the sum of the parts In cells the coordinated interaction between organelles and the regulation of cellular/molecular events At the tissue level the cell surfaces and junctions allow communications and coordination of a larger scope