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Cell-Cell Interactions AP Biology Tissues AP Biology Levels of Organization AP Biology Cells stick together to form tissue AP Biology Levels of Organization How do individual cells “connect” to form tissue? AP Biology Interactions between cells Gap junction Desmosome Tight junction Which is anchoring and why? Which is involved in permeability between cells and how is that permeability mediated? Which is a communication junction? Which is most similar to the plasmodesmata (in plants) and why? AP Biology Transport across membranes Plasma membranes can join together to form tight junctions Adherens junctions membranes “glued” together by proteins - pass through both membranes and attach to cytoskeletons Desmosomes proteins “button” two membranes together AP Biology AP Biology Tight Junctions Zonulae Occludens forms a band completely around the cell fusing cells together and closing off intercellular space Fusion site # often correlates to “leakiness” Fewer fusion sites greater permeability to water and solutes More fusion sites less permeable… In what How would the # organs would you Of fusion sites expect Affect permeability? few fusion sites? Cells of the proximal renal tubule of the kidney where filtration often takes place have few fusion sites to allow for leakability, whereas, cells of the urinary bladder (that must hold urine and not allow it to leak out) contains numerous fusion sites or tight junctions to form a seal to prevent the flow of materials between epithelial cells. AP Biology Tight Junctions Proteins interact to form tight junctions AP Biology You do not need to know these specific proteins. Gap Junctions A gap between neighboring cell membranes Gap Junction (communicating junction) AP Biology Gap Junctions Connexin surrounds the pore, - acts like a hydrophilic ion channel between cells Individual unit of the gap junction = connexon AP Biology Desmosome Anchoring junctions Does not surround cell Adhesion is strengthened by intermediate filaments (keratin) Hemidesmosome = half a desmosome AP Biology Plant Cell Wall AP Biology Plasmodesmata Intercellular connections between adjacent plant cells AP Biology Plasmodesmata AP Biology Summary Adhering junctions: Desmosome & hemidesmosome Impermeable junctions: Tight junctions Communicating junctions: Gap junctions (and in plants, plasmodesmata) AP Biology