Question

hi, regarding the electron transport chain:

why when talking about NADH + H+, we talk about giving electrons rather then proton? this really confuses me..

where is it more potonated and where more ionized? metrix or intracellular or extracellular?

Fe-Sulf is concidered what? I mean it recieves electrons and moves them forward so whats the name of this kind of molecule?

is NADH recruited by FMN? who makes it get to comples I?

thanks in advance

Answer 1

Answere : Reduced NAD+ and FAD (i.e., NADH + H+ or FADH2) released in glycolysis and Kreb cycle, finally reduce oxygen to H20. This transfer of H+ and e- from NADH + H+ or FADH2 to O2 is not a simple process and infact the direct transfer of electron from coenzyme to O2 is thermodynamically not possible. It is because of the fact that NADH2 get oxidised at redox potential of - 0.32 V whereas 02 is reduced at redox potential of + 0.82 V. To facilitate this transfer, many intermediate cytochromes and other carriers having thier intermediate redox potential are arranged in a series which transport electron from NADH2 or FADH2 to O2. This sequence of electron carrier constitute electron transport chain. It is located in inner mitochontrial membrane.

The electron transport down to the energy gradient through electron transport system leads to formation of ATP from ADP and inorganic phosphate. This is called oxidative phosphorylation.

Component of ET system : 4 types of cytochrome b, 2 type of cytochrome c, ubiquinone, flavoprotein (FMN or FAD), iron-sulphur protein (Fe-S) and enzyme cytochrome oxidase which is intimately associated with cytochrome a and a3. ATPase complex.

The inner mitochondrial membrane is permeable to water but impermeable to proton and othet ions except at the point where electron transport chain(ETC) and ATPase system are plugged in membrane. The ETC is oriented in such a way that electrons move in an inward direction (i.e. inside the mitochondrial membrane) and proton flows in an outward direction (i.e. ouside the mitochondrial membrane and in mitochondrial space).

Reduced NADH, released from Krebs cycle, when enters in ETC transport 3 pair of proton(H+) across inner mitochondrial membrane to the space. Similarly, NADH from glycolysis and FADH2 from kreb cycle transport proton(i.e 2 pair of proton) mitochondrial space.

The unidirection flow of proton towards outer side results in the accumulation of H+ in the mitochondrial space. The pH of outer surface of inner mitochondraial membrane lower considerably. It also generate a proton concentration gradient. The pH gradiemt and proton concentration gradient across membrane generate proton motive force. The proton moves from mitochondrial space to mitochondrial matrix through ATPase complex in inner mitochondrial space. ATPase drives ATP synthesis.