nicotinamide adenine dinucleotide
Definition
Nicotinamide adenine dinucleotide (noun) 1. A crucial coenzyme in cellular metabolism: A coenzyme found in nearly all living cells. It is derived from the B vitamin nicotinic acid (niacin). Its primary biological role is to act as a reductant, meaning it donates electrons (and a proton, as a hydride ion) in various metabolic processes, facilitating energy transfer within the cell.
Examples of Usage
- The enzyme used nicotinamide adenine dinucleotide as a cofactor to catalyze the oxidation of the substrate.
- Cellular respiration depends on the redox cycling of nicotinamide adenine dinucleotide between its oxidized (NAD⁺) and reduced (NADH) forms.
- Researchers measured the nicotinamide adenine dinucleotide levels to assess the metabolic activity of the cells.
Advanced Usage
- Redox states: The molecule exists in two interconvertible forms: the oxidized form (NAD⁺) and the reduced form (NADH). The ratio of NAD⁺ to NADH is a key indicator of a cell's metabolic state.
- Substrate for enzymes: It serves as an essential substrate for major classes of enzymes, including dehydrogenases, reductases, and sirtuins, which are involved in pathways like glycolysis, the citric acid cycle, and oxidative phosphorylation.
Variants and Related Words
- NAD (noun): The standard abbreviation for nicotinamide adenine dinucleotide.
- The assay detects the fluorescence of reduced NAD.
- NAD⁺ (noun): Specifically denotes the oxidized form of the coenzyme.
- Sirtuins are a class of enzymes that require NAD⁺ for their deacetylase activity.
- NADH (noun): Specifically denotes the reduced form of the coenzyme.
- NADH carries high-energy electrons to the electron transport chain.
- Nicotinamide adenine dinucleotide phosphate (NADP⁺/NADPH) (noun): A closely related coenzyme that carries an additional phosphate group and is primarily used in anabolic (biosynthetic) reactions, such as photosynthesis and fatty acid synthesis.
Synonyms
- Coenzyme I (noun): An older, less common name for NAD.
- Diphosphopyridine nucleotide (DPN) (noun): A historical name for NAD, now largely obsolete.
Related Phrases and Concepts
- Electron carrier (noun phrase): A descriptive term for the primary function of NAD⁺/NADH in shuttling electrons during metabolic reactions.
- Redox cofactor (noun phrase): A general term for a molecule like NAD that participates in oxidation-reduction reactions.
- Cellular metabolism (noun phrase): The broad set of chemical processes for which NAD is essential.
Noun
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a coenzyme present in most living cells and derived from the B vitamin nicotinic acid; serves as a reductant in various metabolic processes
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