Triphosphopyridine nucleotide

Triphosphopyridine nucleotide (also known as TPN or NADP+) is a coenzyme found in all living cells. It is a derivative of vitamin B3 (niacin) and plays a crucial role in various biological processes, including cellular respiration, photosynthesis, and DNA repair.

Structure

The structure of triphosphopyridine nucleotide consists of two nucleotides joined through their phosphate groups. One nucleotide contains an adenine base and the other contains nicotinamide. The nicotinamide moiety can be attached in two orientations, giving rise to two distinct forms of the coenzyme, NADP+ and NADPH.

Function

Triphosphopyridine nucleotide is involved in many redox reactions, carrying electrons from one reaction to another. The coenzyme is, therefore, found in two forms in cells: NADP+ is an oxidizing agent that accepts electrons from other molecules and becomes reduced, forming NADPH. NADPH is a reducing agent that donates electrons to other molecules, becoming oxidized to NADP+.

Role in Photosynthesis

In photosynthesis, NADP+ plays a crucial role in the light-dependent reactions, where it is reduced to NADPH by the photosystem I complex. The NADPH produced is then used in the Calvin cycle to reduce carbon dioxide to glucose.

Role in Cellular Respiration

In cellular respiration, NADP+ is used in the pentose phosphate pathway, an alternative to glycolysis. This pathway generates NADPH and pentoses (5-carbon sugars) as well as ribose 5-phosphate, a precursor for the synthesis of nucleotides.

Role in DNA Repair

NADP+ is also involved in the process of DNA repair. The coenzyme provides the reducing power needed for the repair of oxidative DNA damage.

See Also

• Nicotinamide adenine dinucleotide
• Coenzyme
• Cellular respiration
• Photosynthesis
• DNA repair

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