Umsebenzi we-Mitochondria eNqubweni Yokuphefumula Kwamaselula
Ama-Mitochondria avame ukubizwa ngokuthi "izindawo zamandla" zamaseli ngoba akhiqiza iningi lamandla adingekayo empilweni. Lawa mandla asetshenziselwa izinqubo ezahlukahlukene, kusukela ekuncipheni kwemisipha kanye nokuthuthwa kwezinto ezidlula emangqamuzaneni kuya ekuhlukanisweni kwamaseli kanye nokuhlanganiswa kwama-molecule abalulekile. Esimweni sebhayoloji, amandla asetshenziswa ngqo ngamaseli ngokuyinhloko asesimweni se-ATP (adenosine triphosphate). Iningi elikhulu le-ATP likhiqizwa ngokuphefumula kwamaseli, futhi i-mitochondria idlala indima ebalulekile kule nqubo.
Isakhiwo se-Mitochondrial Njengomsebenzi Osekelayo
Ukuze uqonde umsebenzi we-mitochondria ekuphefumuleni kwamaseli, kubalulekile ukuqonda isakhiwo sawo esiyisisekelo. Ama-Mitochondria anezimbotshana ezimbili: ulwelwesi lwangaphandle olungena kalula kanye nolwelwesi lwangaphakathi olukhetha kakhulu. Ulwelwesi lwangaphakathi lwakha izimbotshana ezibizwa ngokuthi ama-cristae. Lawa ma-fold andisa indawo engaphezulu yolwelwesi lwangaphakathi, anikeze isikhala esengeziwe sezimpendulo ezikhiqiza i-ATP.
Ngaphakathi kwe-membrane yangaphakathi kukhona i-mitochondrial matrix, uketshezi oluqinile oluqukethe ama-enzyme abalulekile, i-DNA ye-mitochondrial, kanye nama-ribosome. Ukuba khona kwe-DNA nama-ribosome kubonisa ukuthi i-mitochondria inekhono elilinganiselwe lokukhiqiza amanye amaprotheni ngokwawo, yize iningi lamaprotheni ayo lisafakwa ikhodi yi-DNA yenuzi yeseli. Isikhala esiphakathi kwe-membrane yangaphandle neyangaphakathi sibizwa ngokuthi isikhala se-intermembrane, esidlala indima ebalulekile ekwakhekeni kwe-proton gradient ngesikhathi sokuphefumula.
Lesi sakhiwo esinezingqimba asiyona nje indlela, kodwa siwumklamo ofaneleka kahle kakhulu ekwenzeni inqubo eyinkimbinkimbi nenezinyathelo eziningi yokuphefumula kwamaseli.
Ukubuka Konke Kokuphefumula Kwamaselula
Ukuphefumula kwamaseli kuwuchungechunge lwezindlela zamakhemikhali ezihlukanisa ama-molecule okudla—ikakhulukazi i-glucose—ukuze kukhiqizwe i-ATP. Le nqubo ingahlukaniswa ngezigaba eziningana eziyinhloko: i-glycolysis, i-pyruvate oxidation, umjikelezo we-Krebs (umjikelezo we-citric acid), uchungechunge lokuthuthwa kwama-electron, kanye ne-oxidative phosphorylation. Kulezi zigaba, i-glycolysis yenzeka ku-cytoplasm, kanti izigaba ezilandelayo zenzeka ku-mitochondria. Ngamanye amazwi, i-mitochondria iyizikhungo eziyinhloko zokukhiqizwa kwamandla e-aerobic.
Indima yeMitochondria Ngemva kweGlycolysis
I-Glycolysis iphula i-molecule eyodwa ye-glucose ibe ama-molecule amabili e-pyruvate, ikhiqize inani elincane le-ATP ne-NADH. Kodwa-ke, i-ATP ekhiqizwa yi-glycolysis yodwa ayanele ukuhlangabezana nezidingo zamandla zamaseli amaningi. Yilapho i-mitochondria ingena khona.
I-pyruvate evela ku-glycolysis ingena ku-mitochondria ngamaprotheni okuthutha akhethekile ku-membrane yangaphakathi. Ngaphakathi kwe-matrix, i-pyruvate idlula ku-oxidation ye-pyruvate (ebizwa nangokuthi i-bridging reaction) ku-Acetyl-CoA. Le nqubo ikhiqiza i-NADH futhi ikhipha i-CO₂ njengomkhiqizo olandelanayo. I-Acetyl-CoA "iyithikithi lokungena" esigabeni esilandelayo, umjikelezo we-Krebs.
Umjikelezo weKrebs ku-Mitochondrial Matrix
Umjikelezo we-Krebs wenzeka ku-mitochondrial matrix futhi uhlose ukukhipha amandla engeziwe ku-acetyl-CoA. Kulo mjikelezo, i-acetyl-CoA ihlangana ne-oxaloacetate ukuze yakhe i-citrate, bese kuba nochungechunge lwezimpendulo ze-enzyme ukuze ibuyele ku-oxaloacetate. Phakathi nale nqubo, i-CO₂ iyakhishwa bese kwakheka ama-molecule e-electron carrier anamandla aphezulu njenge-NADH ne-FADH₂. Umjikelezo we-Krebs uphinde ukhiqize inani elincane le-ATP (noma i-GTP, kuye ngohlobo lweseli).
Nakuba umjikelezo we-Krebs ukhiqiza i-ATP, umnikelo omkhulu we-mitochondria emandleni eseli empeleni uvela emikhiqizweni ye-NADH ne-FADH₂. Lawa ma-molecule amabili aphethe ama-electron anamandla aphezulu azosetshenziswa ezinyathelweni ezilandelayo.
Uchungechunge Lokuthutha Ama-Electron ku-Mitochondrial Inner Membrane
I-membrane yangaphakathi ye-mitochondrial yindawo yeketanga lokuthuthwa kwama-electron (ETC), inethiwekhi eyinkimbinkimbi yamaprotheni nama-molecule athwala ama-electron. Ama-electron avela ku-NADH kanye ne-FADH₂ adluliselwa kusuka kwenye i-complex aye kwenye. Lokhu kudluliswa kwama-electron kukhulula amandla kancane kancane, kunokuba kukhishwe konke ngesikhathi esisodwa, okuvumela ukusetshenziswa kahle.
Amandla akhishwe asetshenziselwa ukupompa ama-ion e-H⁺ (ama-proton) kusuka ku-matrix angene esikhaleni se-intermembrane. Lokhu kudala umehluko ekugxilweni kwe-proton kanye nokushaja kukagesi phakathi kwe-matrix kanye nesikhala se-intermembrane. Lo mehluko ubizwa ngokuthi i-electrochemical gradient noma i-proton motivation force. Lo gradient umelela "amandla angase abe khona" abe esesetshenziswa ukukhiqiza inani elikhulu le-ATP.
Ekupheleni kochungechunge lokuthuthwa kwama-electron, ama-electron ekugcineni amukelwa yi-oxygen (O₂) bese ehlangana nama-proton ukwakha amanzi (H₂O). Yingakho i-oxygen ibaluleke kakhulu ekuphefumuleni kwe-aerobic: ngaphandle kwe-oxygen njenge-electron acceptor yokugcina, uchungechunge lokuthuthwa kwama-electron belungama, futhi ukukhiqizwa kwe-ATP kwehle kakhulu.
I-ATP Synthase kanye ne-Oxidative Phosphorylation
I-ATP synthase iyi-enzyme enkulu efakwe kulwelwesi lwangaphakathi lwe-mitochondrial. Le enzyme isebenza njenge-turbine yama-molecule. Njengoba ama-proton egeleza esuka esikhaleni se-intermembrane eya ku-matrix nge-ATP synthase, amandla okugeleza kwe-proton asetshenziselwa ukuhlanganisa i-ADP kanye ne-inorganic phosphate (Pi) ukwakha i-ATP. Le nqubo yokwakheka kwe-ATP, eqhutshwa yi-NADH/FADH₂ oxidation kanye nokugeleza kwe-proton, ibizwa ngokuthi i-oxidative phosphorylation.
I-oxidative phosphorylation inegalelo elikhulu le-ATP ekuphefumuleni kwamaseli e-aerobic. Ngokuvamile, i-molecule eyodwa ye-glucose ingakhiqiza cishe i-ATP engu-30-32 (leli nani liyahlukahluka kuye ngezimo zamaseli kanye nohlobo "lwe-shuttle" oluthwala i-cytoplasmic NADH iye kwi-mitochondria). Kulokhu, ingxenye enkulu kakhulu ivela emsebenzini we-electron transport chain kanye ne-ATP synthase ku-mitochondria.
Kungani uKrista Ebalulekile?
Ama-Cristae ayimigoqo ye-membrane yangaphakathi eyandisa indawo engaphezulu lapho kwenzeka khona uchungechunge lokuthuthwa kwama-electron kanye ne-ATP synthase. Uma ama-cristae amaningi, indawo engaphezulu yokusabela kwe-ATP iba nkulu. Yingakho amaseli anezidingo zamandla aphezulu—njengamaseli emisipha yenhliziyo—ene-mitochondria eminingi kanye nama-cristae athuthuke kakhulu. Lesi sakhiwo sibonisa ubudlelwano obuqondile phakathi kwezidingo zamandla zeseli kanye nekhono le-mitochondria lokukhiqiza i-ATP.
I-Mitochondria kanye nokulawulwa kwe-Energy Metabolism
Ngaphezu kokukhiqiza i-ATP, i-mitochondria nayo idlala indima ekulawuleni ukusebenza kweseli. I-Mitochondria ingalungisa izinga lokuphefumula kwayo ngokwezidingo zamandla. Lapho amangqamuzana edinga amandla engeziwe, izinga lokusetshenziswa kwe-ATP liyakhula, ukukhiqizwa kwe-ADP kuyakhula, futhi i-oxidative phosphorylation iyasheshiswa. Ngokuphambene nalokho, uma izidingo zamandla zincipha, izinga lokuphefumula nalo liyancipha. Ngakho-ke, i-mitochondria ayigcini nje ngokukhiqiza amandla kodwa futhi isiza ekugcineni ibhalansi yamandla eseli.
Umphumela Wezinkinga Zokusebenza Kwe-Mitochondrial
Uma umsebenzi we-mitochondrial uphazamiseka, ukukhiqizwa kwe-ATP kuyancishiswa futhi amaseli angaba nokucindezeleka kwamandla. Ngaphansi kwezimo ezithile, i-mitochondria ingakhiqiza nama-free radicals (ROS) njengomkhiqizo ophumayo weketanga lokuthuthwa kwama-electron. Ngamanani alawulwayo, i-ROS ingadlala indima ekudluliseleni kweseli, kodwa amanani amaningi angalimaza amaprotheni, amafutha, kanye ne-DNA. Umonakalo we-mitochondrial uvame ukuhlotshaniswa nezinkinga ezahlukene zempilo kanye nokuguga, yize ingxoxo idlulela ngale kokuphefumula kwamaseli.
Isiphetho
I-Mitochondria idlala indima ebalulekile ekuphefumuleni kwamaseli e-aerobic ngokwenza izinyathelo ezibalulekile ezilandela i-glycolysis, ikakhulukazi i-pyruvate oxidation, umjikelezo we-Krebs, uchungechunge lokuthuthwa kwama-electron, kanye ne-oxidative phosphorylation. Isakhiwo esiyingqayizivele se-mitochondria—ene-membrane yayo yangaphakathi egoqekile eyakha i-cristae, i-matrix, kanye nesikhala se-intermembrane—sisekela ukukhiqizwa kwe-ATP okuphumelelayo ngokwakhiwa kwe-proton gradient kanye nesenzo se-ATP synthase. Ngalezi zinqubo, i-mitochondria inikeza amandla abalulekile ukuze iseli lenze imisebenzi yokuphila. Ngakho-ke, ukuqonda umsebenzi we-mitochondria ekuphefumuleni kwamaseli kusho ukuqonda enye yezindlela eziyinhloko zokuphila ezingeni lamaseli.
