10-6-08_lecture_diffusionA

10-6-08_lecture_diffusionA - The advancement and diffusion...

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The advancement and diffusion of knowledge is the only guardian of true liberty. James Madison Tick : Nobody mucks around with the Tick's bodily membranes. Prepare for swift justice
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Announcements Quiz #3 is due at noon today Quiz # 4 will become available by this afternoon. It will be due next Wednesday 10/15 at noon. It will cover from multisubstrate kinetics through today’s lecture. 2008 Nobel Prize in Medicine Harald zur Hausen for his discovery of "human papilloma viruses causing cervical cancer" and the other half jointly to Françoise Barré-Sinoussi and Luc Montagnier for their discovery of "human immunodeficiency virus“ http://nobelprize.org/nobel_prizes/medicine/laureates/2008/ press.html
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Lateral diffusion is by far the main form of movement within membranes Tail movements are fastest Lateral motions are fast, occurring on microsecond scales Phospholipid flipping is quite infrequent (< 1/day) Flipping can be sped up by enzymes (called flippases)
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FRAP: Not just for staying awake in class Fluorescence Recovery After Photobleaching Technique for focally selecting a patch of membrane to observe its motions within the membrane. Photobleached region size and location can be controlled by laser In other experimental preparations, photobleaching is undesirable
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Protein motion is more restricted and regulated than lipid motion A. random diffusion B. Tethered by interactions with membrane skeleton C. Transported via interactions with cytoplasmic motor protein D. Motion restricted by other proteins in cluster E. Constrained within “fence” of membrane proteins F. Restricted by interactions with extracellular matrix
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Different sides of the same plasma membrane can have different functions and compositions In an example intestinal epithelial cell, the apical membrane takes in glucose and Na+ The lateral membrane forms tight junctions with neighboring cells and is involved in intercellular communication The basal membrane anchors the cell to the intestinal wall and maintains ion gradients in the cell
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Border control Movement and transport around and through the membrane ell icron
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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 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 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 s molecules flowing through a cross- sectional area A within a given time t. D
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10-6-08_lecture_diffusionA - The advancement and diffusion...

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