NADH and NADPH in Cellular Metabolism

NADH vs. NADPH: Where is each one used and why that instead of the other?

NADH (nicotinamide adenine dinucleotide) and NADPH (nicotinamide adenine dinucleotide phosphate) are two important coenzymes involved in cellular metabolism. They both play crucial roles in energy transfer and electron transport within the cell, but they have distinct functions in different cellular processes.

NADH:
NADH is primarily involved in catabolic reactions, which are responsible for breaking down molecules to provide energy for the cell. It is a product of the citric acid cycle (also known as the Krebs cycle) and glycolysis, both of which occur in the mitochondria. NADH is reduced during these reactions when it accepts hydrogen (H) and electrons (e-) from the breakdown of glucose or other fuel molecules like fats and proteins. The reduced form, NADH, carries these high-energy electrons to the electron transport chain (ETC) in the mitochondria

In the ETC, NADH transfers the electrons to oxygen, which facilitates the production of adenosine triphosphate (ATP) through oxidative phosphorylation. This means that NADH acts as a carrier of high-energy electrons to power the generation of ATP, the energy currency of the cell. NADH is typically oxidized back to NAD+ once it donates its electrons

NADPH:
Unlike NADH, NADPH is mainly involved in anabolic reactions, which build molecules and store energy. It is synthesized through the pentose phosphate pathway, which occurs in the cytoplasm. NADPH is reduced during the reactions of this pathway when it accepts hydrogen and electrons. The reduced NADPH acts as a supplier of reducing power in biosynthetic pathways, facilitating the synthesis of macromolecules such as lipids, nucleic acids, and proteins

NADPH also serves as a vital coenzyme in various enzymatic reactions, including those involved in detoxification processes. For instance, it plays a critical role in the function of the enzyme glutathione reductase, which converts oxidized glutathione (GSSG) to reduced glutathione (GSH) – an important antioxidant in cells

In summary, NADH is mainly used in catabolic reactions to transfer high-energy electrons to the electron transport chain and produce ATP, whereas NADPH is primarily involved in anabolic reactions and acts as a reducing agent for biosynthetic processes and enzymatic reactions. The functional differences between NADH and NADPH are a result of their distinct roles in cellular metabolism and the specific requirements of different cellular processes

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