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Lecture 14

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Wilfrid Laurier University
Matthew Smith

Clicker question answers:  Following statement about allosteric enzymes is correct: o Activity can be finely controlled by metabolites within cell  Enzymes are: o Able to recognize and alter specific substrates (reactants)  Organisms living in a hypersaline and alkaline lake would be expected to have enzymes w/ optimal activity at pH > 7  Functions of Membranes o  They aren't just barriers  What is a Cell Membrane? o Permeability membranes; consists of:  Phospholipids, glycolipids, and membrane proteins  Sterols (except in bacteria):  Cholesterol (animals)  Ergosterols (fungi)  Phytosterols (plants)  Membrane proteins  Include:  Integral proteins (usually transmembrane)  Peripheral membrane proteins  Fluid Mosaic Model of Cell Membrane o Membranes aren't rigid o Consist of fluid lipid bilayer where proteins are embedded and float freely o  Fluid Mosaic Model is Supported by Experimental Evidence: Membranes are Fluid o  Cell Chem Review o Properties of water  Polarity  Water as a solvent o Hydrophilic  "likes water" o Hydrophobic "fears water"   Water Molecules are Polar o Polarity --> uneven charge distribution o Electronegative oxygen atom associates w/ electropositive hydrogen atoms of adjacent water molecules to form hydrogen bonds  Hydrogen bonds are important in DNA and proteins o Lololololol  o Polarity  Uneven distribution of charge within molecule o  Water is bent (not linear) at angle of 104.5  Although whole water molecule is uncharged, oxygen atom tends to draw electron toward it, making oxygen and electronegative, and leaving other ends with partial positive charge around hydrogen atoms  Extensive association of water molecules w/ each other is due to hydrogen bonds b/w electronegative oxygen atom of one water molecule and electropositive hydrogen atoms of adjacent molecules  Hydrogen bond is type of noncovalent interaction (about 1/10th as strong as covalent bond)  Individual hydrogen bonds are weak but combined they're strong  Typical bond has half-life of few microseconds but, on avg, liquid water molecule is hydrogen-bonded to at least three neighbouring molecules at any time  Tendency of adjacent water molecules to form hydrogen bonds is what makes
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