3-The Importance of Weak and Strong Chemical bonds

《3-The Importance of Weak and Strong Chemical bonds》由会员上传分享，免费在线阅读，更多相关内容在教育资源-天天文库。

1、幻灯片1TheImportanceofWeakandStrongChemicalBondsChapter3幻灯片2A.CharacteristicsofChemicalBondsB.FreeEnergyC.WeakbondsinbiologicalsystemsD.HighEnergyBondsE.MoleculesthatDonateEnergyAreThermodynamicallyUnstableF.EnzymesLowerActivationEnergiesinBiochemicalReactions

2、幻灯片3G.FreeEnergyinBiomoleculesH.HighEnergyBondsDriveBiosynthesisI.ActivationofPrecursorsinGroupTransferReactions幻灯片4Basedonwhattheycouldseewithmicroscopes,scientistsinthe1900sthoughtcellswereverysimple.Theythoughtcellswerebagsfilledwithalivingsubstancenamed

3、theynamedprotoplasm.Theythoughtprotoplasmwasmadeofsimplechemicalslikeionsandaminoacids.幻灯片5Atthattimemostscientiststhoughtthemoleculesinsidecellswereallverysmallandwereheldtogetherbyweakassociationssuchashydrogenbonds.幻灯片6Inthe1900sscientiststherewasnometho

4、dformeasuringthesizesofmolecules.Basedonwhattheyknew,mostscientistshadnoideaoftheexistenceofmacromolecules(高分子)—largepolymermoleculesthatmakeupcells.幻灯片7Organicchemistshadsynthesizedmoleculesthatwereabout4,000Daltons(道尔顿).Scientiststhoughtthatmoleculeslarge

5、rthanthisdidnotexist.幻灯片8In1901EmilFischerdiscoveredthataminoacidsarelinkedbypeptidebondstoformproteins.Hethoughtthelongestpolypeptidecouldbenolongerthan30to40aminoacids.Anythinglongerwasconsidered“veryimprobable”byalltheleadingchemists.Itwastoodifficulttoi

6、maginehowaminoacidscouldbejoinedtogetherinthecorrectordertoproducelargerproteins.EmilwontheNobelPrizeforhisworkin1902.幻灯片9Otherscientistsbegantoconsidertheexistenceoflargermoleculesbasedonobservingthebehavioroflargemoleculesinsolution.Forexample,somemolecul

7、essuchascellulose(纤维素)wouldnotdiffusethroughafinefilter(滤纸).Butothersthoughtthiscouldbeexplainedbytheweakbondingbetweensmallermolecules.幻灯片10Howcouldthescientistsdeterminewhetherthereweremanysmallmoleculesthatassociatewithweakbondsorwhethertherewerelargemol

8、ecules?幻灯片11Scientistswerelimitedbythetechniquesthatwereavailableatthetime,andtherewasnomethodfordeterminingthesizeoflargemolecules.Thischangedin1925whenTheodorSvedberginventedtheultracentrifuge(超速离心机)