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NAD FAD and Coenzyme A Are Formed from ATP

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NAD FAD and Coenzyme A Are Formed from ATP
III. Synthesizing the Molecules of Life
25. Nucleotide Biosynthesis
25.4. Key Steps in Nucleotide Biosynthesis Are Regulated by Feedback Inhibition
Figure 25.16. Control of Purine Biosynthesis. Feedback inhibition controls both the overall rate of purine biosynthesis
and the balance between AMP and GMP production.
III. Synthesizing the Molecules of Life
25. Nucleotide Biosynthesis
25.5. NAD+, FAD, and Coenzyme A Are Formed from ATP
Nucleotides are important constituents not only of RNA and DNA, but also of a number of key biomolecules considered
many times in our study of biochemistry. NAD+ and NADP+, coenzymes that function in oxidation-reduction reactions,
are metabolites of ATP. The first step in the synthesis of nicotinamide adenine dinucleotide (NAD+) is the formation of
nicotinate ribonucleotide from nicotinate and PRPP.
Nicotinate (also called niacin or vitamin B6) is derived from tryptophan. Human beings can synthesize the
required amount of nicotinate if the supply of tryptophan in the diet is adequate. However, nicotinate must be
obtained directly if the dietary intake of tryptophan is low. A dietary deficiency of tryptophan and nicotinate can lead to
pellagra, a disease characterized by dermatitis, diarrhea, and dementia. An endocrine tumor that consumes large amounts
of tryptophan in synthesizing the hormone and neurotransmitter serotonin (5-hydroxytryptamine) can lead to pellagralike symptoms.
An AMP moiety is transferred from ATP to nicotinate ribonucleotide to form desamido-NAD+ . The final step is the
transfer of the ammonia generated from the amide group of glutamine to the nicotinate carboxyl group to form NAD+.
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