Thenatureofgeneticmaterial
Definition:Thematerialthattransmitsgeneticinformationbetweenparentsandoffspring.
Chemicalnature:ExceptforsomeviruseswhosegeneticmaterialisRNAandprionswhosegeneticmaterialisprotein,thegeneticmaterialsofothervirusesandallorganismswithatypicalcellstructureareDNA.
Existencepart:Thissubstanceisthemaincomponentofthechromosome.Italsoexistsinorganellessuchasplastidsandmitochondriaoutsidethenucleus.
Basiccharacteristics:Relativestability,self-replication,continuitybetweenthepreviousgenerationsandgenerationsandcanproduceheritablemutations.
Conclusion:Thegeneticmaterialofmostorganisms(cell-structuredorganismsandDNAviruses)isDNA,soDNAisthemaingeneticmaterial.
Conditions
1Canaccuratelyreplicateitselfduringcellgrowthandreproduction
2Canstorehugegeneticinformation
3canguideproteinsynthesis,therebycontrollingmetabolismandbiologicaltraits
4cantransmitgeneticinformationbetweenoffspring
5structureisstable,andcanproduceheritablemutations.
Exploratoryprocess
Transformationprocess
Thepurposeoftheexperiment:tostudywhoisthegeneticmaterialinDNAandprotein.Testprinciple:TypeSpneumococcuscancausepneumoniainhumansorsepsisinsmallanimals;TypeRpneumococcushasbasicallynoeffectonhumansandanimals.
Transformationtest
Inthetest,Averyetal.foundthatthehigherthepurityoftheDNA,themoreeffectivethetransformation.
Experiment
provedthatT2bacteriophageisavirusthatspecificallyparasitizesE.coli,andDNAisthegeneticmaterial.
Reconstructiontest
ProvethatinaviruswithonlyRNAbutnoDNA,RNAisthegeneticmaterial.
5)Prions
Thediscoveryofprionsconfirmsthatproteinscanexistasgeneticmaterialoforganismsundercertaincircumstances.
Gettoknow
Discoveryofprions
Prionsareproteinviruses,theyareviruseswithonlyproteinsbutnonucleicacids.Thewinnerofthe1997NobelPrizeinMedicineorPhysiology,AmericanbiologistS.B.Prusiner(S.B.Prusiner)wasawardedthishonorforhisoutstandingcontributionstothestudyofprions.Prionsarenotonlycloselyrelatedtohumanhealthandlivestockbreeding,butalsoprovideimportantinformationforthestudyofotherdiseasesrelatedtodementia.
Asearlyasthreehundredyearsago,humansfirstdiscoveredprion-infectedanimalsinsheepandgoats.Becauseofthedifficultitchingofsickanimals,itoftenrubsonroughtreetrunksandstonesurfaces,sothatthehaironthebodyiswornoff,whichiscalled"sheeppruritus."ThediseasespreadswidelyinEuropeandAustralia,withanincubationperiodof18to26months.Thediseasedanimalsareexcited,itchy,paralyzeduntildeath.Later,infectiousminkencephalomalacia,chronicwastingdiseaseinreddeeranddeer,spongiformencephalopathyincats,etc.werediscoveredoneafteranother.Pathologicalstudieshaveshownthatthesediseasesallinvadethecentralnervoussystemofanimals.Asthediseaseprogresses,progressivevacuolizationoccursinneuronaldendritesandcellsthemselves,especiallyinastrocytesanddendriticcellsinthecerebellum.Glialhyperplasiaandspongylesionsappearingraymatter.Thesediseasesaremainlycharacterizedbyalongincubationperiod,aslowcourseofdisease,progressivebraindysfunction,recoverywithoutremission,anddeath.
Thedomesticanimalprionthathasbecomethefocusofhumanattentionwaswhenthe"madcowdisease"spreadintheUnitedKingdominthespringof1996.ItnotonlycausedanunprecedentedeconomicandpoliticalturmoilintheUnitedKingdom,butalsospreadtotheentireEurope.Reutzfeld-Jacob'sdisease(Crutzfeldt-Jakobsyndrome,apriondiseaseofhumans)hasincreased,andpeoplearenaturallyassociatedwitheatingimportedbeeffromtheUK,whichhascausedgreatpanic.AlthoughitwaslaterfoundthatthemaincauseofFrenchCreutzfeldt-Jakobsyndromewasiatrogenicinfection,otherexamplescouldnotruleouttheconnectionbetweenmadcowdiseaseandhumanpriondisease.
Thefollowingfourtypesofhumanprionshavebeenfound,namelyKurudisease,Creutzfeldt-Jakobsyndrome,Gerstmannsyndromeandfatalfamilyinsomnia.ThemaincharacteristicsoftheirsymptomsandpathologicalchangesareThesyndromeisverysimilartothesickanimal.Amongthem,theresearchonKurudiseaseistheearliest.Kurudisease(Kurudisease)isalocalepidemicinthePapua-NewGuinea-easternForehighlandresidentsintheAtlanticOceaninthefirsthalfofthe20thcentury.Itsmainsymptomsaretremor,ataxia,anddementia.Lossofexerciseability,anddeathduetoexhaustionwithin3to6months."Kuru"means"fear"or"chills"inthetribe,sothediseaseiscalledKurudisease.Thetotalnumberofpatientsisabout30,000,mostlywomenandunderagechildren.TheAmericanmedicalscientistGeDusekconductedresearchintheareafor20years,andfoundthattheoccurrenceofthediseasewascloselyrelatedtothesacrificeoflocalpeople'sconsumptionofhumanflesh,andproposedpreventivemeasures.Aftertheritualwasstoppedin1968,thediseasewasbroughtundercontrol,thussavingatribeofpeople.Forthis,Gedusekwonthe1976NobelPrizeinMedicine.
Thespecificactivitiesandreplicationmechanismsofprionsarenotveryclear,buttheyaregenerallyconsideredtocauseaseriesofpreviouslypoorlyunderstoodinfectiousspongiformencephalopathy,theseencephalopathyincludingscrapieWagyuspongiformencephalopathy(alsocalled"madcowdisease").Theeffectsofthesediseasesonthestructureofbraintissuearefatalandincurable.
Thegeneticmechanismofprions
Itisthemechanismofprionreplicationthatattractsthemostinterestandattentionoftoday'sscientists.Becauseprionsaremolecularorganismsthatonlycontainproteinbutnonucleicacid,theycanonlysurviveinparasitichostcells.Therefore,theinformationneededtosynthesizeprionsmaybepresentinthehostcells,andtheroleofprionsisonlytoactivatethegenesencodingtheprionsinthehostcellssothattheprionscanreplicateandreproduce.
Anothertheoryisthatprionproteinscanencodegeneticinformationforthemselves.Thishypothesisiscontrarytothe"centrallaw"intraditionalmolecularbiology,becauseprionshavenonucleicacid.Therefore,itisassumedthatthepossiblemethodofprionreplicationisthattheRNAorDNAencodingtheprionisproducedthroughtheprocessofreversetranslation(reversetranscriptionisrequiredinthelattercase).Theremustbeareversetranslationenzyme,andevenareversetranscriptase..Thesecondisproteinsynthesisundertheguidanceofprotein,thatis,proteinitselfcanbeusedasgeneticinformation.
In1982,Pruzinaproposedthe"proteinconformationaldiseasehypothesis"thatprionscausedisease,whichwasgraduallyimprovedbyWeismanetal.Themainpointsareasfollows:①Prionproteinhastwoconformations:celltype(normalPrPc)anditchytype(pathogenicPrPsc).Themaindifferencebetweenthetwoliesintheirspatialconformation.PrPconlyhasahelix,whilePrPschasmultipleβsheets,thelatterhaslowsolubilityandisresistanttoproteolysis;②PrpsccanforcePrPctotransformintoPrpsc,realizeself-replication,andproducepathologicaleffects;③GenemutationcanleadtocelltypePrPscTheα-helixstructureinthemediumisunstable,andspontaneoustransformationoccurswhenacertainamountisreached,andtheβ-sheetincreases,andfinallybecomesthePrpsctype,whichmultipliesthediseasethroughthedominoeffect.
Althoughthegeneticmechanismofprionsisnotyetfullyunderstood,asfarasbiologicaltheoryisconcerned,thereplicationofprionsdoesnotusenucleicacidsastemplates,butproteinsastemplates.ThisisboundtobeusefulfortheexplorationoflifeTheoriginandthenatureoflifephenomenahaveamajorimpact.