英语翻译thus the final product of oxidative metabolism is water,

英语翻译
thus the final product of oxidative metabolism is water,which
is not an impressive result in itself.Recall,however,what
happened in the process of forming that water.The electrons contributed by NADH molecules passed down the electron transport chain,activating three proton-pumping channels.Similarly,the passage of electrons contributed by FADH2 ,which entered the chain later,activated two of these channels.the electron harvested from the citric acid cycle have in this way been used to pump a large number of protons out across the membrane,and that result is the pay-off of oxidative respiration
in eukaryotes,oxidative metabolism takes place within the mitochondria,which are persent in virtually all eukaryotic cells.the internal compartment or matrix of a mitochondrion contains within it the enzymes that perform the reactions of the citric acid cycle.electrons harvested there by oxidative respiration are used to pump protons out of the matrix into the outer compartments,the space between the two mitochondrial membranes.as a high concentration of protons builds up,protons cross the inner membrane back into the matrix,driven by diffusion.the only way they can get in is through special channels,which are visible in electron micrographs as projections on the inner surface of the membrane.the proton channel is made up of four polypeptide chains that traverse the membrane.at the inner boundary of the membrane,the channel is linked by a stalk of several proteins to a large protein complex composed of five polypeptide chains.this protein complex synthesizes ATP within the matrix when protons travel inward through the channel.the ATP then passes out of the mitochondrion by facilitated diffusion and into the cell's cytoplasm.

因此,氧化反应的最终产物是水,这完全不让人吃惊.然而,再回忆一下在生成水的过程中所发生的一切.NADH分子在降低电子传递链时产生了电子,激活了三个质子泵通道.同样,FADH2产生的电子随后又进入到此传递链,激活其中两个通道.柠檬酸循环产生的电子在这里将大量的质子从细胞膜中释放出来,这也是真核细胞有氧呼吸的结果,氧化反应发生在线粒体中,这些线粒体实际上存在于所有真核细胞中.线粒体的内膜或基质中含有酶从而促进柠檬酸反应,此反应中的有氧呼吸所产生的电子将质子从基质中释放到外膜层,也就是两线粒体细胞膜之间的空隙中.由于此时质子的浓度升高,于是质子通过扩散穿过内膜又回到基质中.这些粒子可以进入的唯一方法是通过特殊通道,这一点,通过对膜的内表面电镜可以观测到.质子通道是由横贯细胞膜的四条肽链组成.在细胞膜的内边界上,此通道被几个蛋白质结构连接到一个由5条肽链组成的大的蛋白质复合体上,当质子穿过通道向内扩散时,此蛋白复合体会在基质中合成ATP,随后ATP通过扩散从线粒体中出来进入到细胞质中.
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