English
Hemoglobinmolecule
Introduction
Thehemoglobinmoleculeisamolecularmachinewithextremelyhighworkingefficiency.ItusesmotionandsmallstructuresChangetoadjustitsbehavior.Thecombinationofoxygenandhemoglobinatthefoursitesisnotsynchronized.Thefirstcombinationofoxygenandhemoglobincausessmallchangesinthecorrespondingproteinchains.Thesechangesmakeiteasierforthemtobindtooxygen.So,althoughitisdifficulttocombinethefirstoxygen,itbecomeseasierandeasiertocombinethesecond,third,andfourth.Thisfacilitatesthefunctionofhemoglobin.Whenbloodflowsthroughtheoxygen-richlungs,oxygeneasilycombineswiththefirstsubunit,andthenquicklyfillstheotherparts.Thenwhenthebloodcirculatesinthebody,theoxygenconcentrationdropsandthecarbondioxideconcentrationrises.Inthiscase,hemoglobinreleasesoxygen.Onceoneoxygenisseparated,hemoglobinchangesshape,whichmakestheotherthreeoxygensbereleasedquickly.Inthisway,hemoglobinisloadedwiththemaximumamountofoxygeninthelungsandthentransportedtotheaerobictissue.Inthisanimation,asubunitofhemoglobinisfixedinoneplace,sowecanseehowhemoglobinmovesarounditwhenitbindsoxygen.Oxygenisshowningreen.Whenoxygenbindstotheironinthehemecenter,itpullsupthehistidineatthebottomofthehemoglobin.Thiscausesthepositionoftheentirealphahelixtomove,whichisindicatedinorangeundertheheme.Thismovementistransmittedtootherproteinchains,andfinallycausesthetwobluesubunitstoroll.
Molecularstructure
1hemoglobinmoleculeiscomposedof1globinand4heme(alsocalledferroprotoporphyrin).Eachhemeiscomposedof4pyrrolylgroupstoformaringwithaferrousioninthecenter.Globinhas4polypeptidechains,andeachpolypeptidechainisconnectedtoahemetoformamonomerorsubunitofHb.Hbisatetramercomposedof4monomers.
Hemoglobinisaproteinresponsibleforcarryingoxygeninhigherorganisms.
Thehemoglobininthehumanbodyiscomposedoffoursubunits,twoαsubunitsandtwoβsubunits.ThefoursubunitsofhemoglobincanbeassembledautomaticallyinanelectrolytesolutionsimilartothehumanenvironmentIntotheformofα2β2.
Eachsubunitofhemoglobiniscomposedofapeptidechainandahememolecule.Underphysiologicalconditions,thepeptidechainwillbecoiledandfoldedintoasphericalshape,holdingthehememoleculeinside,andthispeptidechainiscoiledintoThesphericalstructureisalsocalledglobin.Thehememoleculeisasmallmoleculewithaporphyrinstructure.Inthecenteroftheporphyrinmolecule,thefournitrogenatomsonthepyrroleringintheporphyrincoordinatelybindtoaferrousion,andtheoneatthe8thpositionintheglobinpeptidechainThenitrogenatomontheindolesidechainofthehistidineresiduecoordinatedwiththeferrousionfromabovetheplaneoftheporphyrinmolecule.Whenhemoglobinisnotboundtooxygen,theremaybeawatermoleculefrombelowtheporphyrinring.Theferrousioniscoordinatedandbound,orthecoordinationsiteisempty,andwhenthehemoglobincarriesoxygen,theoxygenmoleculecanreplacethepositionofthewater.