Difference Between NAD and NADP

Main Difference – NAD vs NADP

NAD and NADP are two types of coenzymes used in cellular metabolism. Both compounds are used to carry electrons from one reaction to another. Thereby, both NAD and NADP contain an oxidized and reduced form. The reduced form of the NAD is NADH while the oxidized form is NAD⁺. In NADP, the reduced form is NADH and the oxidized form is NADP⁺. The main difference between NAD and NADP is that NAD is used in cellular respiration whereas NADP is used in photosynthesis.

Key Areas Covered

1. What is NAD
      – Definition, Features, Function
2. What is NADP
      – Definition, Features, Function
3. What are the Similarities Between NAD and NADP
      – Outline of Common Features
4. What is the Difference Between NAD and NADP
      – Comparison of Key Differences

Key Terms: Cellular Respiration, Coenzyme, NAD, NAD⁺, NADP, NADPH, Photosynthesis

What is NAD

NAD (nicotinamide adenine dinucleotide) refers to a coenzyme involved in the oxidation-reduction reactions of cellular respiration inside the cell. It is used in the glycolysis, Krebs cycle, fatty acid synthesis and sterol synthesis. Dehydrogenases, hydroxylases, and reductases are the enzymes that use NAD as an electron carrier. NAD⁺ is the oxidized form of the NAD while NADH is the reduced form. The structures of both NAD⁺ and NADH are shown in figure 1.

Figure 1: NAD+ and NADH

NAD⁺ serves as an electron and hydrogen acceptor while NADH serves as an electron and hydrogen donor. NAD⁺ is used to obtain electrons from the catabolizing reactions in the cell such as glycolysis and Krebs cycle. This produces NADH. NADH carries electrons to the electron transport chain. In the electron transport chain, ATP is produced by removing electrons from NADH.

What is NADP

NADP (nicotinamide adenine dinucleotide phosphate) refers to a coenzyme involved in the oxidation-reduction reactions inside the cell. It is mainly used in the anabolic reactions such as nucleic acid and lipid synthesis. NADPH is the most abundant form of NADP inside the cell, which acts as a reducing agent. It structurally differs from NAD by the presence of an additional phosphate group in the 2’ position of the ribose, which carries the adenine moiety. The structure of the NADP⁺ is shown in figure 2.

Figure 2: NADP+

NADPH is produced in the light reaction of photosynthesis by the enzyme ferredoxin-NADP+ reductase. Its reduction power is used in the Calvin cycle, assimilating carbon dioxide. In animals, NADP is used in the pentose phosphate pathway.

Similarities Between NAD and NADP

Both NAD and NADP are coenzymes used in the cellular metabolism.
NAD and NADP are the most abundant coenzymes inside the cell.
Both NAD and NADP are nucleotides.
Both NAD and NADP carry electrons from one reaction to another.
Both NAD and NADP have an oxidized and a reduced form.
Both NAD and NADP contain two ribose rings, an adenine moiety.

Definition

NAD: NAD is a coenzyme involved in the oxidation-reduction reactions in the cellular respiration inside the cell.

NADP: NADP is a coenzyme involved in the oxidation-reduction reactions inside the cell.

Use

NAD: NAD is used in cellular respiration.

NADP: NADP is used in photosynthesis.

Phosphate Group

NAD: NAD does not contain a phosphate group.

NADP: NADP contains a phosphate group at the 2’ position of the ribose ring, which carries the adenine moiety.

Reduced Form

NAD: NADH is the reduced form of NAD.

NADP: NADPH is the reduced form of NADP.

Oxidized Form

NAD: NAD⁺ is the reduced form of the NAD.

NADP: NADP⁺ is the oxidized form of the NADP.

Abundance

NAD: The oxidized form of NAD is most abundant inside the cell.

NADP: The reduced form of NADP is most abundant inside the cell.

Role

NAD: NAD⁺ is mostly used as an oxidizing agent.

NADP: NADPH is mostly used in catabolic reactions.

Pathways

NAD: NAD is used in glycolysis, Krebs cycle, fatty acid synthesis and sterol synthesis.

NADP: NADP is used in Calvin cycle, pentose phosphate pathway, lipid synthesis, fatty acid chain elongation, and cholesterol synthesis.

Conclusion

NAD and NADP are the most abundant coenzymes in the cells, which are used in oxidation-reduction reactions. Both NAD and NADP are structurally similar but, NADP contains a phosphate group. NAD is mainly used in the cellular respiration and electron transport chain whereas NADP is used in the photosynthesis. This is the difference between NAD and NADP.

Reference:

1. “What is Nicotinamide Adenine Dinucleotide (NAD)?” Study.com, Available here.
2. “NADPH: Definition, Structure & Function.” Study.com, Available here.

Image Courtesy:

1. “Figure 07 01 01ab” By CNX OpenStax (CC BY 4.0) via Commons Wikimedia
2. “NADP+ phys” By NEUROtiker – Own work (Public Domain) via Commons Wikimedia