Coenzymes

Most of the biochemical pathways in living things are enhanced by the control proteins called enzymes. The efficiency of the enzyme-catalyzed reactions is often increased by the presence of helper molecules called coenzymes. A coenzyme present in every living cell is NAD⁺. It participates in electron transport reactions in cell metabolism processes like glycolysis. Another essential coenzyme is FAD which also contributes to the electron transport process.

Much of the energy from the TCA cycle in aerobic respiration is used to reduce the coenzymes, thereby giving their electrons higher energy for the electron transport reactions.

The reduced coenzyme NADPH plays a key role in the Calvin cycle for the production of carbohydrates in photosynthetic organisms.

Reduced Coenzymes as Energy Storage Elements

Most of the biochemical pathways in living things are enhanced by the control proteins called enzymes. The efficiency of the enzyme-catalyzed reactions is often increased by the presence of helper molecules called coenzymes. A coenzyme present in every living cell is NAD⁺. It participates in electron transport reactions in cell metabolism processes like glycolysis. Another essential coenzyme is FAD which also contributes to the electron transport process.

Much of the energy from the TCA cycle in aerobic respiration is used to reduce the coenzyme NAD⁺ to NADH, which is used to give electrons higher energy for the electron transport reactions.

In photosynthetic organisms, the light energy drives the electron transport chain of chloroplasts. Much of the energy is used to reduce the coenzyme NADP⁺ to form NADPH, thereby raising it to a higher energy state. The energy of NADPH is then used in the Calvin cycle as a part of the process of carbohydrate synthesis.

Dehydrogenases and Reductases

Most of the biochemical pathways in living things are enhanced by the control proteins called enzymes which are assisted by smaller structures called coenzymes. In the general processes of metabolism in living organisms, both the catabolic and anabolic processes are aided by enzymes.

A dehydrogenase is an enzyme that assists catabolic processes by oxidizing substrates, reducing electron receptors like NAD⁺/NADP⁺ and flavin coenzymes such as FAD or FMN. Dehydrogenases oxidize a substrate by transferring hydrogen into an electron acceptor.

This is an example of a dehydrogenase using the coenyzme NAD⁺ to accomplish an oxidation.

A reductase is an enzyme that catalyzes a reduction reaction. Reduction is characteristic of the anabolic side of metabolism. Reduction and oxidation (redox reactions) are both extensively used in metabolism.