10-5-09_lecture_diffusionB

10-5-09_lecture_diffusionB - 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 # 4 will become available by this afternoon. It will be due this Friday 10/9 at noon. It will cover from multisubstrate kinetics through today’s lecture.
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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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Integral membrane proteins are transmembrane proteins Have domains that extend into cytoplasm and extracellular space May constitute 20-30% of all proteins encoded in cell Typically span membrane with hydrophobic alpha helix Amphipathic Examples include ion channels and transporters, both which typically bind a substance on one or both sides
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Hydropathy plots are used to identify membrane spanning regions of a protein Hydropathy plots show the amount of free energy required to move amino acids to an aqueous medium. Given 1.5 A between peptides and 30 A bilayer, takes at least 20 amino acids to span membrane Typically a running average window of 10+ residues
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Determining which portions of a transmembrane protein are extracellular or intracellular
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Peripheral membrane proteins are held onto one membrane surface by NON-covalent bonds Located entirely on inner or outer surface Held to membrane only by non- covalent bonds
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Lipid-anchored proteins are covalently tethered to the cytoplasmic or extracellular surface of the membrane Covalent link is to a lipid molecule Lipid can be PI, fatty acid, etc.
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Border control Movement and transport around and through the membrane ell icron
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Diffusion in a liquid or within the membrane is the motion from a high to low concentration. • The change in concentration along a spatial dimension is the concentration gradient. Diffusion can be passive , in which molecules move from high to low concentrations along the concentration gradient or facilitated , in which molecules are chaperoned across the membrane along the gradient • Transport can be active , in which molecules move from low to high concentrations against the concentration gradient. Active transport requires energy.
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10-5-09_lecture_diffusionB - The advancement and diffusion...

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