6715_Lecture%204_cell%20diffusion

6715_Lecture%204_cell%20diffusion - IV-1 Lecture IV Cell...

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1 PHYS 6715 - Lecture IV 1 Lecture IV Cell – Transport and Diffusion 1. Introduction 2. Microscopic Modeling 3. Transport 4. Cell Cycle and Division 5. Apoptosis and Cancer PHYS 6715 - Lecture IV 2 IV-1 Introduction Transport through cellular membrane • Two types of transport exist: passive and active . • Passive transport requires no energy from cell, a molecule or ion moves spontaneously crossing the membrane down a concentration (entropy increasing) or electric potential gradient (energy decreasing). • Passive transport can be further divided into the three categories: diffusion, osmosis, and facilitated diffusion. •A c t i v e transport moves molecules up their concentration or electric potential gradient (entropy decreasing and/or energy increasing) thus requires energy from the cell in forms of ATPs (protein pumps). PHYS 6715 - Lecture IV 3 IV-1 Introduction Transport through cellular membrane Passive transport • Diffusion refers to the net transportation of an element (often small molecules such as H 2 O, O 2 , CO 2 , C 2 H 5 OH (ethanol) and CON 2 H 4 (urea)) along its concentration gradient. Diffusion is due to thermal fluctuation and its rate depends on temperature, structure (existence of membrane, etc.) and local molecular interaction Example: O 2 concentration is higher outside than inside of a cell Æ O 2 diffuses into the cell; the opposite is true for CO 2 . •O s m o s i s is defined as the net movement of water as the solvent through a semipermeable membrane driven by a difference in solute concentrations on the two sides of the membrane • Facilitated diffusion is the net transportation of large molecules (glucose, Na + and Cl - ) across the cellular membrane "facilitated" by proteins that span the membrane because the lipid bilayer of the membrane is virtually impermeable to these molecules PHYS 6715 - Lecture IV 4 IV-1 Introduction Transport through cellular membrane • Passive transport - example PHYS 6715 - Lecture IV 5 IV-1 Introduction Transport through cellular membrane • Active transport - example PHYS 6715 - Lecture IV 6 IV-1 Introduction Diffusion – macroscopic description • A solution is a type of mixture in which one substance, called the solute , is uniformly distributed throughout another substance, usually a liquid, called the solvent . • Solute concentration can be expressed by the following terms: molarity c = moles of solute / volume of solution (liter) Æ unit: molar (M) molality m = moles of solute / mass of solvent (kg) mole fraction = moles of solute / moles of solution percent mass = 100xmass of solute / mass of solution
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2 PHYS 6715 - Lecture IV 7 IV-1 Introduction Diffusion – macroscopic description • Example: If we dissolve 1.00 mole of sucrose (about 342.3g) in water to make 1.00 liter of solution (sugar water), then the molarity is given by c=1(mol/L)=1(M) •E x a m p l e : 2.9g of NaCl are dissolved in 100mL of water. Then the molality m of the resulting solution is given by m=(2.9g/58.44g/mol)/(100cm 3 x1.0g/cm 3 )=0.496 (mol/kg) PHYS 6715 - Lecture IV 8 Diffusion – macroscopic description • Adolf Fick’s first law: j
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This note was uploaded on 01/21/2012 for the course PHYS 6720 taught by Professor Hu during the Spring '10 term at East Carolina University .

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6715_Lecture%204_cell%20diffusion - IV-1 Lecture IV Cell...

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