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11_21 - The brain is a wonderful organ it starts working...

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The brain is a wonderful organ; it starts working the moment you get up in the morning and does not stop until you get into the office. Robert Frost Tick : You know... I've heard the smarter you are, the more wrinkly your brain. And your guys' brains must be the wrinkliest. Oh, sure, ordinary Joes like me and Arthur here, maybe our brains are a little on the smooth side. But you don't have to be a genius to know that evil is bad. And good isn't.
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Announcements Quiz 8 due Tuesday 11/22 at 5 pm. CELLLS part 2 due Wednesday Dec. 7 at 5 pm.
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Examples of each type of movement across the membrane O2 and nonpolar substances can passively diffuse across (slowly) When a channel is opened, ions flow along their electrochemical gradient Glucose entry is facilitated by a glucose transporter (Facilitated diffusion) Na-K ATPase is an exchange mechanism that uses energy to transport both ions against their concentration gradient, from [Low] to [High].
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The time to diffuse a given length is approximately t=(length) 2 /D D is the diffusion coefficient. D=100 μ m 2 /s in this example, typical for a small molecule such as ATP Diffusion is ok for short distances (about 100 μ m) It would take about 3 hours to diffuse 1 mm for this D
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The rate of diffusion is given by Fick’s Law For a solute s , the rate of diffusion of s is given by Q s / t=D s x A x C s / x, Q is the quantity of solute molecules (s) flowing through a cross-sectional area A within a given time t. D s is the diffusion coefficient that is specific to the solute/solvent conditions. 2200 ∆ C s / x is the concentration gradient 2200 ∆ Q s / t is also referred to as the flux J.
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Our respiratory and circulatory systems use very large areas, steep concentration gradients, and relatively short paths to transport oxygen via diffusion Our lung alveoli together form a surface area the size of a tennis court!
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Active transport: Na+/K+-ATPase example Na + out =150 mM, Na + in =15 mM : E Na =+60 mV K + out =5 mM, K + in =100 mM : E K = -78 mV
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