METABOLISMO (002) - CICLO DE KREBS E CADEIA RESPIRATÓRIA
Autor: Professor Thiago Rennó | Publicado: 2013-09-26T06:51:00-07:00

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Em
nosso organismo, quando quebramos a glicose em piruvato, tomamos vias
metabólicas conhecidas como metabolismo aeróbio.



Esta
denominação é dada pelo fato de que a produção de ATP está diretamente ligada
com a presença do oxigênio molecular (O2) em nossas células.



O
metabolismo aeróbio ocorre nas mitocôndrias e tem como suas principais vias:



-
o ciclo de Krebs, do ácido cítrico ou do ácido oxalacético;



-
a cadeia respiratória.



Ao
final deste ciclo será formada a maior quantidade de ATP de todo o metabolismo
da glicose, fornecendo energia suficiente para as funções orgânicas.



O
início das vias aeróbias é dado quando o piruvato chega a matriz mitocondrial e
une-se à coenzima A.



Esta
reação libera um carbono na forma de CO2.



Como
resultado temos um ácido acético (acetato) ligado à coenzima, conjunto
conhecido como Acetil-CoA.



O
objetivo do ciclo de Krebs é degradar o acetato liberando mais dióxido de
carbono e íons hidrogênio para redução de coenzimas NAD+ e FAD+
em NADH+H+ e FADH2.



Todo
o CO2 produzido segue é difundido para o sangue e eliminado pela respiração
pulmonar.



As
coenzimas reduzidas continuam na mitocôndria e, na crista mitocondrial
participam da cadeia respiratória, onde o oxigênio será liberado, somado ao
oxigênio molecular e formará moléculas de água.



Para
tanto, as enzimas transportadoras de elétrons responsáveis por esta reação
liberam uma grande quantidade de energia, gerando, no final das duas vias
metabólicas, 18 ATPs para cada piruvato.



Como
resultado final - somando-se aos dois produzidos no saldo na via glicolítica –
temos o total de 38 ATPs para cada molécula de glicose.







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