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Questions and Answers
What is the effect of defects in urea cycle on pyrimidine synthesis?
What is the effect of defects in urea cycle on pyrimidine synthesis?
What is the source of the methyl group in the synthesis of Deoxythymidine Monophosphate?
What is the source of the methyl group in the synthesis of Deoxythymidine Monophosphate?
What is the product of the degradation of pyrimidine ring?
What is the product of the degradation of pyrimidine ring?
What is the enzyme responsible for the synthesis of Cytidine Triphosphate?
What is the enzyme responsible for the synthesis of Cytidine Triphosphate?
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What is the inhibitor of the enzyme responsible for the generation of tetrahydrofolate?
What is the inhibitor of the enzyme responsible for the generation of tetrahydrofolate?
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What is the role of PRPP in pyrimidine synthesis?
What is the role of PRPP in pyrimidine synthesis?
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What is the product of amination of UTP?
What is the product of amination of UTP?
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What is the enzyme responsible for the regulatory step of pyrimidine synthesis?
What is the enzyme responsible for the regulatory step of pyrimidine synthesis?
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What is the precursor for pyrimidine synthesis?
What is the precursor for pyrimidine synthesis?
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What is the purpose of the salvage pathway?
What is the purpose of the salvage pathway?
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What is the role of PRPP in the synthesis of nucleotides?
What is the role of PRPP in the synthesis of nucleotides?
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What is the consequence of releasing Ppi and its immediate hydrolysis in the salvage pathway?
What is the consequence of releasing Ppi and its immediate hydrolysis in the salvage pathway?
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What is the enzyme responsible for the synthesis of 2'-deoxyribonucleotides?
What is the enzyme responsible for the synthesis of 2'-deoxyribonucleotides?
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What is the role of Thioredoxin in the synthesis of deoxyribonucleotides?
What is the role of Thioredoxin in the synthesis of deoxyribonucleotides?
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How is ribonucleotide reductase regulated to supply enough deoxyribonucleotides for DNA synthesis?
How is ribonucleotide reductase regulated to supply enough deoxyribonucleotides for DNA synthesis?
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What is the effect of dATP on ribonucleotide reductase?
What is the effect of dATP on ribonucleotide reductase?
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What is the outcome of binding of nucleotide trisphosphates to additional substrate-specific sites?
What is the outcome of binding of nucleotide trisphosphates to additional substrate-specific sites?
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Where do purine nucleotides degrade?
Where do purine nucleotides degrade?
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Study Notes
Nucleotide Functions
- Nucleotides function as energy carriers (ATP, FAD)
- They are structural components of enzyme cofactors (NAD)
- They act as second messengers in signal transduction (cAMP)
- They are carriers of activated intermediates in the synthesis of carbohydrates, lipids, and conjugated proteins (UDP-glucose)
Nucleic Acid Functions
- They store genetic information (DNA)
- They transmit genetic information (mRNA)
- They process genetic information (ribozymes)
- They are involved in protein synthesis (tRNA and rRNA)
Nucleotide Structure
- Nucleotides are composed of a nitrogenous base, a pentose monosaccharide, and one to three phosphate groups
- Modifications such as methylation, acetylation, and glycosylation can be added to nucleotides
Synthesis of Purine Nucleotides
- Purine ring is built on ribose-5-phosphate in the liver
- Ribose-5-phosphate is produced in the hexose monophosphate shunt of carbohydrate metabolism
- 5-Phosphoribosyl-1-pyrophosphate (PRPP) is an activated pentose that participates in the synthesis and salvage of purines
- Glutamine transfers its amide nitrogen to PRPP to produce 5-phosphoribosylamine, a committed step of synthesis
- The enzyme PRPP glutamyl amidotransferase is controlled by feedback inhibition of nucleotides AMP, GMP, and IMP
Synthesis of Deoxyribonucleotides
- 2'-Deoxyribonucleotides are synthesized from ribonucleoside diphosphates by a reduction of C2 of ribose moiety
- Thioredoxin is a peptide coenzyme of ribonucleotide reductase
- Regulation of deoxyribonucleotide synthesis is controlled by catalytic site and allosteric site
- dATP inhibits the enzyme and prevents synthesis of any four nucleoside diphosphates
Degradation of Purine Nucleotides
- Occurs in the small intestine
- Nucleic acids are hydrolyzed to nucleotides
- Purine bases are not used for the synthesis of nucleic acids
- They are converted to uric acid
Diseases Associated with Purine Degradation
- Lesch-Nyhan syndrome: characterized by excessive uric acid production, neurological abnormalities, and self-mutilation
Synthesis of Pyrimidine Nucleotides
- Pyrimidine ring is synthesized before being attached to a ribose-5-phosphate
- Carbamoyl phosphate is formed from ATP, GLUTAMINE, and CO2
- Pyrimidine ring is converted to the nucleotide orotidine monophosphate (OMP)
- PRPP is the ribose-phosphate donor
Degradation and Salvage of Pyrimidines
- Pyrimidine ring is opened and degraded to highly soluble products, beta-alanine, and beta-aminoisobutyrate
- The pyrimidines can also serve as precursors in the salvage pathway to be converted to the respective nucleotides via phosphorylation
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Description
Explore the structure, synthesis, degradation, and functions of nucleotides and nucleosides. Learn about the diseases associated with the metabolism of purines and pyrimidines. Understand the role of nucleotides as energy sources, enzyme cofactors, and second messengers in signal transduction.
