Purine Synthesis and Inhibition Quiz

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Questions and Answers

What is the primary purpose of the coordinated feedback mechanisms in the biosynthesis of purine and pyrimidine ribonucleotide triphosphates (NTPs) and dNTPs?

To synthesize purine bases in the free form rather than assembling the purine ring piece by piece.

To utilize injected purine or pyrimidine analogs, including potential anticancer drugs, as substrates.

To ensure their production in appropriate quantities and at times that match varying physiologic demand, such as cell division. (correct)

To directly incorporate dietary purines and pyrimidines into tissue.

What is the initial step in the de novo synthesis of purine nucleotides?

The formation of ribose-5-phosphate.

The direct incorporation of dietary purines and pyrimidines into tissue.

The transfer of pyrophosphate group from ATP to ribose-5-phosphate by the enzyme PRPP synthetase. (correct)

The assembly of the purine ring piece by piece with all the intermediates attached to ribose-5-phosphate.

According to the passage, what is the fate of dietary purines and pyrimidines when consumed by humans?

They are not incorporated directly into tissue, even when the diet is rich in nucleoproteins. (correct)

They are directly incorporated into tissue.

They are utilized as substrates for the biosynthesis of purine and pyrimidine ribonucleotide triphosphates (NTPs) and dNTPs.

They are used to synthesize purine bases in the free form rather than assembling the purine ring piece by piece.

How is the purine ring assembled in the de novo synthesis of purine nucleotides?

The purine ring is assembled piece by piece with all the intermediates attached to ribose-5-phosphate. Signup and view all the answers

What is the role of PRPP (Phospho Ribosyl Pyro Phosphate) in the de novo synthesis of purine nucleotides?

PRPP is formed from ribose-5-phosphate by the transfer of pyrophosphate group from ATP by the enzyme PRPP synthetase. Signup and view all the answers

Which compounds inhibit the formation of tetrahydrofolates and block purine synthesis?

Azaserine, diazanorleucine, and mercaptopurine Signup and view all the answers

What is the fate of injected purine or pyrimidine analogs, including potential anticancer drugs, according to the passage?

They are utilized as substrates for the biosynthesis of purine and pyrimidine ribonucleotide triphosphates (NTPs) and dNTPs. Signup and view all the answers

Which enzymes catalyze the formation of adenylate and guanylate in the purine salvage pathway?

Adenine phosphoribosyltransferase and hypoxanthine-guanine phosphoribosyltransferase Signup and view all the answers

From where do the nitrogen and carbon atoms of atoms 4, 5, and 7 of the purine ring derive?

Glycine Signup and view all the answers

Which pathway is known for saving energy by recycling purine bases?

Purine Salvage pathway Signup and view all the answers

Which compounds inhibit the Purine Salvage pathway?

Azaserine, diazanorleucine, and mercaptopurine Signup and view all the answers

What do free purine bases attach to in order to form purine nucleoside monophosphates?

PRPP Signup and view all the answers

Study Notes

Purine and Pyrimidine Nucleotide Biosynthesis

Coordinated feedback mechanisms regulate the biosynthesis of purine and pyrimidine ribonucleotide triphosphates (NTPs) and dNTPs to maintain proper cellular levels.

De Novo Synthesis of Purine Nucleotides

The initial step in the de novo synthesis of purine nucleotides is the formation of PRPP (Phospho Ribosyl Pyro Phosphate) from ATP and ribose-5-phosphate.
The purine ring is assembled from various amino acids and carbon dioxide, with nitrogen and carbon atoms 4, 5, and 7 derived from aspartate, glutamine, and glycine.
PRPP plays a crucial role in the de novo synthesis of purine nucleotides, serving as a reactant for the formation of the first purine nucleotide, inosinic acid.

Fate of Dietary Purines and Pyrimidines

Dietary purines and pyrimidines are degraded to uric acid and excreted, with no net synthesis of nucleotides occurring.

Purine Salvage Pathway

The purine salvage pathway recycles purine bases, saving energy by reusing existing purine rings.
The enzymes adenine phosphoribosyltransferase and hypoxanthine-guanine phosphoribosyltransferase catalyze the formation of adenylate and guanylate in the purine salvage pathway.
Free purine bases attach to PRPP to form purine nucleoside monophosphates.
Anticancer drugs and other analogs are metabolized and incorporated into nucleic acids, affecting their structure and function.
Methotrexate and sulfanilamide inhibit the formation of tetrahydrofolates, blocking purine synthesis.
Azaserine and Hadacidin inhibit the purine salvage pathway.

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Description

Test your knowledge on purine synthesis, inhibition, and salvage pathways. Learn about the sources of nitrogen and carbon atoms in the purine ring and the compounds used in cancer chemotherapy to block purine synthesis.