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Lecture 7

Biology Lecture 7 Outcomes

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Western University
Biology 1002B
Tom Haffie

Lecture 7 Membranes  Membranes are not all lipid, some are more than 50% protein  Lipid is backbone Lipid Biology  Lipids have both hydrophobic and hydrophilic groups in same molecule o Amphipathic: hydrophobic have both hydrophilic properties o Ex. detergents  Internal Fatty acids= hydrophobic o Hydrophobic affect is spontaneous reaction where fatty acid tails groups together in an aqueous environment  External phosphate heads= hydrophilic Fatty Acid structure  Fatty acid layer: hydrocarbons  Saturated fatty acids= linear, can’t add more H o Butter, margarine, lard  Unsaturated= kink, double bond, double bond o Fewer than max # H possible o Trans unsaturated: H are across from each other  Banned, unhealthy, acts like saturated fats o Cis unsaturated: “kinkier” H on same side  More common than trans fats  Ie vegetable oil  Molecules very Diverse o Can by varying length o Vary in number of bonds, types, and position  Fluidity of membrane o affected by structure o temperature (high temp= low fluidity) o affected by saturated fat level (more saturated fat= less fluid)  Keeping membrane at right fluidity is vital (for transport of molecules thru it) within a certain range o To make room for molecules to go thru  Ectotherm: body environment controlled by environmental temperature  Endotherms: us, we control our temperature Physiological Importance of Unsaturation  Fat is first synthesized as a saturated fat  Desaturases enzyme introduce carbon double bonds o Transcription for desaturase varies with temp  Bacteria like warm environments  Level of desaturase activity varies with temperature o Cold temps= more activity to make it more fluid Membrane Permeability  Small molecules are let in thru simple diffusion  Large molecules and charge impede simple diffusion  Transmembrane Proteins help cross these molecules  Hydrophobic portions of protein face outwards o nonpolar amino acids here  Hydrophilic face the inner channel  Alpha helix minimizes charged of backbone so proteins can interact with hydrophobic core Transemebrane Protein Prediction  Given a primary sequence, active site, charges can’t be figure out  But you can determine whether it’s a membrane spanning protein  Takes 20 amino acids to cross a membrane o Those 20 are more nonpolar than the rest of the protien  Above left, there should be 6 regions of nonpolar amino acids Membrane Transport  Entropy drives diffusion: [high[[low]  Entropy increases when you have e
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