Describe the role of NAD and FAD in transferring hydrogen to carriers in the inner mitochondrial membrane
Describe the role of NAD and FAD in transferring hydrogen to carriers in the inner mitochondrial membrane
Answer
Electron Transport Chain (ETC) and Hydrogen Transfer: The Crucial Role of NAD and FAD
In the process of cellular respiration, the inner mitochondrial membrane plays a pivotal role in generating most of the energy that is produced in the form of ATP. Two essential coenzymes, NAD (Nicotinamide Adenine Dinucleotide) and FAD (Flavin Adenine Dinucleotide), are vital in this process, acting as hydrogen (electron) carriers.
The Role of NAD and FAD in Hydrogen Transfer:
- NAD+ (Oxidized Nicotinamide Adenine Dinucleotide):
- Function: Accepts two electrons (2e-) and two protons (2H+) from the breakdown of carbohydrates, fats, and proteins in the citric acid cycle and fatty acid oxidation, becoming NADH.
- Structure: The nicotinamide moiety is the site where the electron transfer occurs.
- FAD (Flavin Adenine Dinucleotide):
- Function: Similar to NAD+, FAD accepts two electrons (2e-) and two protons (2H+), primarily from the citric acid cycle and fatty acid oxidation, converting to FADH2.
- Structure: The isoalloxazine ring of the flavin group is where electron transfer takes place.
Transfer of Hydrogen to Carriers in the Inner Mitochondrial Membrane:
The reduced forms of these coenzymes (NADH and FADH2) then transfer their electrons (hydrogens) to the Electron Transport Chain (ETC) in the inner mitochondrial membrane. This process is crucial for the generation of ATP:
- NADH:
- Transfers electrons to Complex I (NADH Dehydrogenase) of the ETC.
- Outcome: The electrons pass through a series of protein complexes (Complexes I, II, III, IV), ultimately reducing oxygen to water and pumping protons across the membrane, creating a proton gradient.
- FADH2:
- Enters the ETC at Complex II (Succinate Dehydrogenase), bypassing Complex I.
- Outcome: Similarly, the electrons contribute to the proton gradient, albeit with fewer protons pumped compared to NADH, as FADH2 enters the chain at a later stage.
ATP Synthesis:
The proton gradient established across the inner mitochondrial membrane is utilized by ATP Synthase (Complex V) to produce ATP from ADP and Pi (inorganic phosphate) through the process of chemiosmosis.
Summary:
Coenzyme | Reduced Form | Entry Point in ETC | Outcome |
---|---|---|---|
NAD | NADH | Complex I | Contributes to proton gradient, leading to ATP synthesis |
FAD | FADH2 | Complex II | Contributes to proton gradient, leading to ATP synthesis (with fewer protons pumped) |