Lecture 7-8 220 BlckBd Revised

Lecture 7-8 220 BlckBd Revised - Cell Surfaces and...

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Cell Surfaces and Membranes Junctions and Connectional Structures between Animal Cells - Cells cannot exist in isolation from the external environment. There has to be ways to control what comes in and what goes out. - Cell membranes and surfaces control this function. - We will examine how cell membranes and their associated proteins etc. enable these functions. Cell Membranes - We will examine the structure/function relationships of the various that allow some cell types to associate and/or communicate. Plant Cell Walls
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Cell Surfaces and Membranes Junctions and Connectional Structures between Animal Cells Tight Junctions Desmosomes Gap Junctions Three types:
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Cell Surfaces and Membranes Tight Junctions Form belts around cells. The outer part of the plasma membranes between cells touch each other, and contain membrane proteins - tight junction proteins ( occludins and claudins ) - that act as seals to limit the loss of fluid and ions. Are important for controlling the loss of fluid between one biological compartment and another. For example in the gut, to stop interstitial fluid from leaking into the intestine. Junctions and Connectional Structures between Animal Cells
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Cell Surfaces and Membranes Desmosomes - function as anchors between cells. Intermediate filaments of the cytoskeleton are important components of desmosomes. Gap Junctions - Provide linkage between the cytoplasmic compartments of two cells. Formed from proteins called connexons that form a 'tube' between cells. Important for allowing groups of cells to communicate with one another. Junctions and Connectional Structures between Animal Cells
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Figure 6.32 Intercellular junctions in animal tissues
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Desmosomes
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Desmosome plasma membranes cytoplasmic plaque intermediate filaments Cell 1 Cell 2 Intercellular space (with connecting fibers)
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intermediate filaments and desmosomes
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Intermediate filaments and Desmosomes
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Gap Junctions
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Cell Surfaces and Membranes Plant Cells Walls Plant cells have a cell wall that is secreted by the cell and is made up of 3 components. a thin primary cell wall . a middle lamella , which is sticky and made up of polysaccharides called pectins.This helps stick cells together. as the plant matures, a thicker and less flexible set of secondary cell walls is layered. This is less flexible and can be quite rigid particularly in woody plants. The plant wall consists of a variety of macromolecules, but cellulose is a primary component. Plant cells are not isolated from each other , but are linked by cytoplasmic bridges through the wall structure - plasmodesmata .
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Figure 6.28 Plant cell walls
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Cell Surfaces and Membranes For a cell to function efficiently it must be able to do 2 fundamental things: 1) control its internal environment, ie. what goes on inside the cell.
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