BIOL 3510 1st Edition Lecture 25 Outline of Last Lecture I Telophase II Body and Organ Regulation III Bcl2 IV Extracellular Signals Outline of Current Lecture I Tissues II Tight Junctions III Cell Junctions IV Three Key Mechanisms V Embryonic Stem Cells Current Lecture Tissues are composed of cells and extracellular matrix Cells are the building blocks of multicellular organisms Most of the cells in multicellular organisms are organized into cooperative assemblies called tissues Disorders of tissues renewal are a major medical concern Plant cells have tough external walls Cellulose microfibrils in the plant cell wall confer tensile strength while other polysaccharide components resist compression Cellulose microfibrils give the plant cell wall its tensile strength Microtubules help direct the deposition of cellulose in the plant cell wall Collagen provides tensile strength in animal connective tissues Fibronectin and integrin proteins help attach a cell to the extracellular matrix Gels of polysaccharide and proteins fill spaces and resists compression Cells can be packed together in different ways to form an epithelial sheet These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Tight junctions allow epithelial cell sheets to serve as barriers to solute diffusion Tight junctions make an epithelium leak proof and separate its apical and basal surfaces and are formed from claudins and occludins Several types of cell junctions are found in epithelia in animals Adherens junctions can be used to bend epithelial sheets into tubes Cadherins mediate cell cell attachments Hemidesmosomes attach the basal face of an epithelial cell to the basal lamina This attachment is mediated by transmembrane integrin proteins which are linked to intracellular keratin filaments Gap junctions provide neighboring cells with a direct channel of communication Plant cells are connected via plasmodesmata Three key mechanisms important for maintaining the organization of cells into tissues 1 Cell communication o New cells are produced and survive only when and where they are required 2 Selective cell adhesion o Different cell types have different cadherins and other cell adhesision o Prevents the different cell types in a tissue from becoming chaotically mixed 3 Cell memory o Cells preserve their distinctive character and pass it on to their progeny Stem cells generate a continuous supply of terminally differentiated cells ES cells derived from an embryo can give rise to all of the tissues and cell types of the body Embryonic stem cells ES cells can proliferate indefinitely in culture and remain capable of differentiating into any cell type in the body pluripotent
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