lecture 2 - 2-1MCB354Lecture 2Reading in Lehninger:Chapter...

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Unformatted text preview: 2-1MCB354Lecture 2Reading in Lehninger:Chapter 2Chapter 3WaterHydrogen BondsAcid-Base ChemistryAmino AcidsThe water molecule is dipolarWater- Oxygen nucleus attracts e-more strongly than hydrogen(ie oxygen is more electronegative)- e-shared unequally, e-more oftenin vicinity of O - unequal e-sharing results in 2 dipolesunshared e-pairsDIPOLE = MOLECULE W.BOTH +ve AND -ve CHARGES0.9914.5--++2-2Hydrogen bond between 2 water molecules2-3Electrostatic attractionbetween -of Oon one water molecule and+of Hon another water molecule= hydrogen bond2.74 betweenheteroatoms2-4H-bonds in biological systems2-5FORM BETWEEN AN ELECTRONEGATIVE ATOM,USUALLY O, OR NWITH A LONE PAIR OF e-AND AN H-ATOMCOVALENTLY BONDEDTO ANOTHER ELECTRONEGATIVE ATOMINSAME ORANOTHERMOLECULE~2 ~1 Some biologically important H-bonds2-6ABILITY OF A MOLECULE TOPARTICIPATE IN H-BONDINGINFLUENCES ITS SOLUBILITYHydrogen bondsH-bonds are l o n g e r and weakerthan covalent bondsH-bondsare strongest when the 3 atoms involved lie in a straight line:Intramolecular H-bondsare important in conferring 3D structure (ie stability) on proteins and nucleic acidsH-atoms covalently bonded to C-atoms do notparticipate in H-bonding(C-H bond v. weakly polar)2-7Water is a polarsolvent:dissolves charged or polar compounds by replacing solute-soluteH-bondswith solute-waterH-bonds.Non-polarmolecules such as lipidsare hydrophobic; side chains ofsome a.a. are referred to ashydrophobic.Amphipathicmolecules have polaror charged regions, as well asnon-polarregions.Compounds that dissolve easily inwater are hydrophilic.2-8Solubility of biological moleculesalcoholsaldehydesketonescompounds containing N-H bondsall form H-bonds with H2O moleculesand tend to be soluble in water.2-9Examples of polar, non-polar, and amphipathicmolecules2-10Waters Polarity is Used to Disrupt ElectrostaticSolute-Solute InteractionsE = (ZeA*ZeB)/(4ODr) = Coulomb EnergyF=E/r Dielectric ConstantElectric Permittivity of Free SpaceDH2O~79Dbenzene~52-11Charge (ionization) can make a molecule soluble...
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This note was uploaded on 01/29/2012 for the course MCB 354 taught by Professor Spees during the Spring '09 term at University of Illinois, Urbana Champaign.

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lecture 2 - 2-1MCB354Lecture 2Reading in Lehninger:Chapter...

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