AreviewofisomersIsomers-Samechemicalformula,differentpropertiesStructural -Stereoisomers['speifal]DifferentbondsSame bonds,different spatialarrangementDiasteriomers-Enantiomerscis vstransmirrorimagesarrangements
[ˈspeɪʃəl ]
AminoAcidsShareCommon StructuralFeatureseea carbon and fourCOOsubstituentsαcarbonisthechiralcenter+HH.NtetrahedralRDifferentsidechain-
Different side chain→
Amino Acid Substituentsfoursubstituents:rerea- a carboxyl groupCOO- an amino group-- a hydrogen atom- an Rgroup (aside6dchain unique to eachHNHaamino acid)o. glycine has asecond hydrogenRatominsteadofanRgroup
TheAminoAcidResiduesinProteins areLStereoisomers.two possiblestereoisomers=H.Nenantiomers(a)D-AlanineL-AlanineopticallyactiveCOOCOOinteract with light differentlyH3N-C-HNHH-DsystemspecifiesCHeCHa(b)L-AlanineD-AlanineabsoluteconfigurationCOO-COO-HaNNH3HMirrorimageofeachother-CH3CH(c)L-AlanineD-Alanine
Mirror image of each other → interact with light differently
Aminoacid chiralityCHOCHOChiral carbon:HOH,CICH20Hbound to 4HOOHdifferent groupsD-GlyceraldehydeL-GlyceraldehydeExcept?[.glisa'raelda,haid]甘油醛COO-COO.MirrorimagesR..IR+H3NNH3+AHD-Amino acidL-Amino acid[livao'raotatan]L=levorotatory,rotatepolarizedlighttotheleftD=dextrorotatory,rotatepolarized lighttotherightAll aminoacidsfound inproteinsareL-enantiomersStereochemistryinaminoacidsplaysroleinoverallproteinstructure
Amino acid chirality L = levorotatory; rotate polarized light to the left D = dextrorotatory; rotate polarized light to the right All amino acids found in proteins are L-enantiomers Stereochemistry in amino acids plays role in overall protein structure [ˌɡlɪsəˈrældəˌhaɪd]甘油醛 [ˌliːvəʊ'rəʊtətərɪ]