Question

Explain how the electron transport chain functions to generate ATP in terms of electron
carriers, oxygen as the electron acceptor, the four inner membrane proteins, the hydrogen
concentration gradient, water and ATP synthase.

Answer 1

Answer-

According to the question-

Electron transport chain- Here the last step of cellular respiration occur in which ATP is produced from the Molecules such as FADH₂ and NADH molecules produced during the krebs cycle. In this process the electrons are transferred from some molecules which act as electron donors to some components which act as electron acceptor to produced ATP in the chain called Oxidative phosphorylation.

• There are four complexes which are made up of protein are called protein complexes such as complex I, complex II, complex III and complex IV used for movement of electron from molecule of NADH, FADH₂ to the last molecule of electron acceptor such as oxygen.
• Protein Complex I are responsible for pumping the hydrogen ions from the mitochondrial matrix to intermembrane space of mitochondrian and generated the proton gradient.
• Protein Complex II is act as receiver of FADH₂, and without going to complex I and transfer its electron to electron transport chain.
• A component present in the membrane called Ubiquinone represented by Q act as receptor of electron from both protein complex I and complex II and transfer the electron to protein complex III
• Protein Complex III responsible for pumping the protons through the intermembrane and also transfer the electron to cytochrome c. later the cytochrome c  transfer to the protein complex IV.
• Protein Complex IV is responsible for reducing the oxygen by transferring two hydrogen ions to oxygen and water formation takes place.

Complex I- is also called NADH dehydrogenase or  NADH- ubiquinone oxidoreductase have a flavoprotein called FMN-with  six centres of iron- sulfur. It is responsible for ransferring the hydride ion from NADH to  ubiquinone as well as the same time pumping of four protons from the mitochondrial matrix to the intermembrane space.

Complex II is also called succinate dehydrogenase, it have FAD as well as iron- sulphur centres. This complex have five prosthetic with four  protein subunits which contains  heme b, and ubiquinone b inding site as well as binding site for succinate. Electrons from the FADH₂ are transferred to iron- sulphur centres followed to the Ubiquinone which later enter into electron transport chain. some molecules other such as glycerol 3-phosphate
dehydrogenase and fatty acyl-CoA dehydrogenase also responsible for transferring the electron from the FADH₂ to Ubiquinone to convert into ubiquinol . Complex II is not involved in transport of protons from the mitochondrial matrix to intermembrane space.

Complex III- also called ubiquinone- cytochrome c oxidoreductase,  or cytochrome bc1 complex. Here transfer of electron from the ubiquinol to cytochrome c as well as the same time pumping of proton from mitochondrial matrix to intermembrane space occur. this is also called Q cycle. cytochrome c is also a electron transferring protein and have heme prosthetic group.

Complex IV- It is responsible for reducing the oxygen by transferring two hydrogen ions to oxygen as well as same time oxidation of reduced cytochrome c  with the help of cytochrome c oxidase and water formation takes place.

ATP synthetase enzyme present in the membrane of mitochondrian.  hydrogen ions or the protons which are pumped across the membrane by several protein complex are used by ATP synthetase. due to pumping of proton from the mitochondrial matrix to intermembrane space produces concentration gradients as well as and electrical gradients due to which the hydrogen ions start diffusing back from the intermembrane space to the matrix  through the integral membrane protein called ATP synthase which are responsible for adding a phosphate group to the ADP molecule to produce ATP molecule .