Lecture_06_signaling-i - 2/3/11 Todays outline: READINGS :...

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2/3/11 1 READINGS : TODAY: CHAPTERS 4+5 Tuesday: CHAPTER 6 1 Cell-cell contacts (chapter 3) movement of molecules across cell membranes Diffusion Facilitated diffusion Active transport Signaling in and between cells Today’s outline: 2 Plasma membrane 3 Cell - Cell contacts: 1) Desmosome 2) Tight junctions 3) Gap junctions 4 Desmosomes provide strong attachments. 20 nm Dense accumulation of proteins and fibers Holds the cells firmly together Areas of considerable stretch (skin) Desmosome : 5 Desmosomes provide strong attachments. Dense accumulation of proteins and fibers Holds the cells firmly together Areas of considerable stretch (skin) Desmosome : 6
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2/3/11 2 Surface of the 2 adjacent PM is joined together. Prevents passage of molecules (other than water and small water soluble mol.) in extra- cellular space. Epythelial cells (I.e. inner surface f the intestinal tract). Tight junction: 7 Surface of the 2 adjacent PM is joined together. Prevents passage of molecules (other than water and small water soluble mol.) in extra- cellular space. Epythelial cells (I.e. inner surface f the intestinal tract). Tight junction: 8 Protein channels linking the cytosol of adjacent cells allows small molecules and ions to pass freely between cells. Allows for direct electrical and chemical communication between cells. Gap Junction : 2-4 nm 9 Protein channels linking the cytosol of adjacent cells allows small molecules and ions to pass freely between cells. Allows for direct electrical and chemical communication between cells. Gap Junction : 10 11 http://www.youtube.com/watch? d Gap juunctions Gap junction inhibitor – therapeutic use? Over time, solute molecules placed in a solvent will evenly distribute themselves. START: Initially higher concentration of molecules randomly move toward lower concentration. Diffusion = movement of molecules as a result of their random thermal motion. Simple diffusion 12
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2/3/11 3 Note: the partition between the two compartments is a membrane that allows this solute to move through it. Net flux accounts for solute movements in both directions. Simple diffusion 13 At time B, some glucose has crossed into side 2 as some cross into side 1. Simple diffusion 14 Diffusion in the biological context The distance of diffusion determines the equilibrium rate. cell 20 um 15 ms to reach equilibrium of [O 2 ]i 265 days to reach equilibrium of [O 2 ]i Therefore diffusion works on the cellular scale (micrometers) and can not work on the organismal level. In the body movement of molecules across long distances is done by bulk flow. 15 Diffusion through membranes J = PA (Co - Ci) J = net flux P = permeability coefficient A = membrane surface area 16 Permeability constant of organic molecules is dependent on their molecular structure . Oxygen, carbon dioxide, steroid hormones, fatty acids all enter
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Lecture_06_signaling-i - 2/3/11 Todays outline: READINGS :...

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