6BB lecture 10-5-09 diffusion, osmosis

6BB lecture 10-5-09 diffusion, osmosis - hapter 7 (pp....

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Chapter 7 (pp. 129-139) – Cell membrane functions Learning objectives: Know the different functions provided by membrane proteins - Explain the different ways substances are moved across membranes by transport proteins Understand the importance of ‘gradients’; effects on and utilization by the cell Distinguish passive from active transport; simple from facilitated diffusion Define osmosis and explain how cells respond to solutions of different tonicity Explain how bulk transport through the cell membrane is accomplished Terms to know include… concentration gradient, diffusion, osmosis, tonicity, hypo-, iso-, hyper-tonic, plasmolysis, turgid, flaccid, aquaporins, membrane potential, electrochemical gradient, proton pump, sodium-potassium pump…
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Figure 6.32 Intercellular junctions – animal cells Tight junctions prevent fluid from moving across a layer of cells Tight junction 0.5 µm 1 µm 0.1 µm Gap junction Extracellular matrix Space between cells Plasma membranes of adjacent cells Intermediate filaments Tight junction Desmosome Gap junctions
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Cell organelles in animation: The Inner Life of the Cell
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(reference Figure 7.9) Figure 7.9 Transport. (left) A protein that spans the membrane may provide a hydrophilic channel across the membrane that is selective for a particular solute. (right) Other transport proteins shuttle a substance from one side to the other by changing shape . Some of these proteins hydrolyze ATP as an energy source to actively pump substances across the membrane. Enzymatic activity. A protein built into the membrane may be an enzyme with its active site exposed to substances in the adjacent solution. In some cases, several enzymes in a membrane are organized as a team that carries out sequential steps of a metabolic pathway. Signal transduction. A membrane protein may have a binding site with a specific shape that fits the shape of a chemical messenger, such as a hormone. The external messenger (signal) may cause a conformational change in the protein (receptor) that relays the message to the inside of the cell. (a (b) (c) ATP Enzymes Signal Receptor Cell-cell recognition. Some glyco-proteins serve as identification tags that are specifically recognized by other cells. Intercellular joining. Membrane proteins of adjacent cells may hook together in various kinds of junctions, such as gap junctions or tight junctions (see Figure 6.32). Attachment to the cytoskeleton and extracellular matrix (ECM). Microfilaments or other elements of the cytoskeleton may be bonded to membrane proteins, a function that helps maintain cell shape and stabilizes the location of certain membrane proteins. Proteins that adhere to the ECM can coordinate extracellular and intracellular changes (see Figure 6.30). (d)
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This note was uploaded on 01/20/2010 for the course BIO 50415 taught by Professor Batterton during the Fall '09 term at University of Texas at Austin.

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6BB lecture 10-5-09 diffusion, osmosis - hapter 7 (pp....

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