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BIO 168 STUDY GUIDE CHAPTERS 4-9 .docx - Study Guide...

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Study Guide (Chapter 4-9) Review:Chapter 4: Things to Know:a.Discuss how cells of a tissue are held together (cell connections):Cell junctions:are contact points between the plasma membranes of tissuecells.Tight junctions:consist of weblike strands of transmembrane proteins that fusetogether the outer surfaces of adjacent plasma membranes to seal offpassageways between adjacent cells. Cells of epithelial tissue that lines thestomach, intestines, and urinary bladder have many tight junctions. They inhibitthe passage of substances between cells and prevent the contents of theseorgans from leaking into the blood or surrounding tissues.Adherens junctions:contain plaque, a dense layer of proteins on the inside ofthe plasma membrane that attaches both to membrane proteins and tomicrofilaments of the cytoskeleton.-Cadherins (transmembrane glycoproteinsinsert into the plaque from theopposite side of the plasma membrane, partially crosses the intercellularspace (the space between the cells) and connects to cadherins of anadjacent cell.-Adhesion belts (extensive zones) epithelial cells:they encircle the cellsimilar to the way a belt encircles your waist. For example, help epithelialsurfaces resist separation during contractile activities, like good movingthrough the intestines.Desmosomes:contain plaque and have transmembrane glycoproteins(cadherins) that extend into the intercellular space between adjacent cellmembranes and attach cells to one another. It doesn’t attach to microfilamentslike adherens does.-Instead, a desmosome plaque attaches to elements of the cytoskeletonknown as intermediate filaments, which consist of the protein keratin. Theintermediate filaments extend from desmosomes on one side of the cellacross the cytosol to desmosomes on the opposite side of the cell. Thisstructural arrangement contributes to the stability of the cells and tissue.These spot weld–like junctions are common among the cells that make upthe epidermis (the outermost layer of the skin) and among cardiac musclecells in the heart. Desmosomes prevent epidermal cells from separatingunder tension and cardiac muscle cells from pulling apart during contraction.
Hemidesmosomes:resemble desmosomes, but they do not link adjacentcells. The name arises from the fact that they look like half of a desmosome.However, the transmembrane glycoproteins in hemidesmosomes areintegrins rather than cadherins. On the inside of the plasma membrane,integrins attach to intermediate filaments made of the protein keratin. On theoutside of the plasma membrane, the integrins attach to the protein laminin,which is present in the basement membrane. Thus, hemidesmosomesanchor cells not to each other but to the basement membrane.

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