Question

Give some details, explain how the carbon monoxide "shut down" the Electron Transport Chain and how it affects human?

Answer 1

Electron transport chain is a series of reactions that relies on protein complexes to transfer electrons from electron donars to electron acceptors through reduction and oxidation (redox) reactions. This electron transfer gets coupled with the transfer of protons across the membrane creating electrochemical proton gradient which drives the ATP synthesis. It has an important role in photosynthesis and cellular respiration.

The main purpose of ETC is to build up a surplus of protons as a result of redox reactions in the intermediate space so that there will be a gradient compared to the matrix of mitochondria.

OVERVIEW OF STEPS IN ELECTRON TRANSPORT CHAIN:

ETC is a process in which NADH and FADH2 produced during glycolysis, β oxidation and other catabolic processes are oxidized releasing energy in the form of ATP by a mechanism called chemiosmotic phosphorolation.

The electrons begin their reactions in Complex I, continuing onto Complex II, transverse to Complex III and cytochrome c through coenzyme Q and then finally to Complex IV. These four complexes actively transfers electrons from organic metabolites continuing the process. For every turn of the protein 3 ATP is produced concluding electron transport chain.

Remember in the above complexes, cytochrome of Complex III and IV plays a vital role in this chain. Cytochrome c reductase of complex III is where the Q cycle takes place. After this step cytochromes then extend into complex IV or cytochrome c oxidase which is a last complex that translocates 4 protons to create the proton gradient which develops ATP at the end.

SHUT DOWN OF ELECTRON TRANSPORT CHAIN BY CARBON MONOXIDE (CO):

CO is a colourless and odorless molecule known as lethal gas and toxic air pollutant.

As said earlier cytochrome has an important role in electron transport chain, the carbon monoxide specifically inhibits cytochrome c oxidase in complex IV of human mitochondrial respiratory chain. This gradual decrease in cytochrome c oxidase significantly shuts down the electron transport chain in mitochondria at subcellular level. Activities of other complexes shows no significant variation to CO.

Hence in Humans carbon monoxide is toxic for mitochondria which alters mitochondrial respiratory chain at cytochrome c oxidase level developing the symptoms of acute CO poisoning and in some diseases of smoking.