What type of reaction produces NADH during metabolism?

NADH is produced in metabolism during reduction reactions, specifically when a molecule undergoes a process that involves the gain of electrons, often coupled with the reduction of NAD+ (Nicotinamide adenine dinucleotide) to NADH. This process is fundamental in various metabolic pathways, such as glycolysis and the citric acid cycle, where substrates are oxidized and NAD+ serves as an electron carrier that accepts electrons and protons, ultimately forming NADH.

In contrast, decarboxylation reactions typically involve the removal of a carboxyl group from a molecule, often resulting in the release of carbon dioxide and do not directly produce NADH. Oxidative phosphorylation refers to a stage in cellular respiration where ATP is produced through the electron transport chain, utilizing NADH, rather than producing it. Reductive phosphorylation is not a standard term in metabolic pathways, and while a reduction process can produce NADH, it is specifically the reduction reactions that are crucial for its formation. Hence, reduction reactions are directly linked to the generation of NADH during metabolic processes.