Question

How is electron energy changed into the energy found in ATP? This is a multi-step process and you should mention the general steps that occur within the electron transport chain (either respiration or photosynthesis) and how ATP is generated.

Answer 1

Respiration

The conversion of electron energy to chemical energy in ATP occurs by a special system called electron transport chain that occurs on inner mitochondrial membrane. In this the electron flow occurs through successive dehydrogenase enzymes. These dehydrogenase enzymes are located on inner mitochondrial membrane as complexes. There are 4 distinct multi protein complex and these are connected by 2 mobile carriers coenzyme Q and cytochrome C.

•Complex 1:also called NADH dehydrogenase complex. It contains flavoprotein consisting of FMN as prosthetic group and an iron sulphur protein (FeS).

•Complex 2:also called succinate Q reductase.

•Complex 3:also called cytochrome reductase.it is a cluster of iron sulphur protein cytochrome b and cytochrome c1.

•Complex 4: also called cytochrome oxidase. Contains different proteins including cytochrome a and cytochrome a3.

Passage of electrons through electron transport chain is in the following manner,

Complex 1:NADH ->FMN->Fes->CoQ->complex 2:succinate ->FAD->FeS->CoQ->complex 3:CoQ->FeS->cyt b->cyt c1->cyt c->complex 4:cyt c->cyt a-a3->oxygen.

●Generation of electrochemical potential across inner mitochondrial membrane.

During mitochondrial electron transport chain NADH or FADH2 is acting as initial electron donor from which electron is transferred to complex 1.from complex 1 electrons are transferred to coenzyme Q this produces energy that pumps 4 protons from mitochondrial matrix to inter membrane space.

Similarly transfer of electron from complex 3 to cytochrome c pumps 4 protons. And transfer of electron from complex 4 to final electron acceptor oxygen pump 2 protons. So through this process the concentration of protons at inter membrane space increases. So there is an eletrochemical potential difference for proton flow from inter membrane space to matrix. And these protons passes through Fo portion of ATP synthase and this catalyses the formation of phospho anhydride bond ATP by F1 portion of ATP synthase complex.

[ATP synthase complex is composed of 2 functional units,Fo and F1.Fo unit spans the inner mitochondrial membrane.it acts as a proton channel through which protons enter mitochondria. F1 subunit projects into matrix. It catalyses ATP synthesis. ]