Adp

Phosphoenolpyruvic acid

Pyruvic acid ure D.1

Figure

Chemical reactions of glycolysis. There is a net production of 2 ATP molecules from each glucose molecule. The four hydrogen atoms released provide high-energy electrons that may be used to generate ATP in the electron transport chain, described later. (Note: By convention, carbon atoms are sometimes numbered from right to left.)

adenine dinucleotide). When NAD+ accepts a pair of hydrogen atoms, the two electrons and one hydrogen nucleus bind to NAD+ to form NADH, and the remaining hydrogen nucleus (a hydrogen ion) is released as follows:

NAD+ is a coenzyme obtained from a vitamin (niacin), and when it combines with the energized electrons it is said to be reduced. Reduction results from the addition of electrons, often as part of hydrogen atoms. Another electron acceptor, FAD (flavine adenine dinucleotide), acts in a similar manner, combining with two electrons and two hydrogen nuclei to form FADH2 (fig. D.2). In their reduced states, the hydrogen carriers NADH and FADH2 now hold most of the energy once held in the bonds of the original glucose molecule.

Shier-Butler-Lewis: I Back Matter I Appendix D: A Closer Look I I © The McGraw-Hill

Human Anatomy and at Cellular Companies, 2001

Physiology, Ninth Edition Respiration/Nucleic Acids

FAD*

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