Podcast
Questions and Answers
What is the principal form of chemical energy available to cells?
What is the principal form of chemical energy available to cells?
- FAD
- CoA
- NAD+
- ATP (correct)
What type of bond connects the base and saccharide in a nucleoside?
What type of bond connects the base and saccharide in a nucleoside?
- Ester bond
- Phosphodiester bond
- β-N-glycosidic bond (correct)
- Anhydride bond
What is the role of phosphotransferase reactions in the cell?
What is the role of phosphotransferase reactions in the cell?
- Muscle contraction and active transport (correct)
- Synthesis of proteins
- Replication of DNA
- Fatty acid synthesis
What is the classification of nucleotides that contain adenine, guanine, hypoxanthine, or xanthine?
What is the classification of nucleotides that contain adenine, guanine, hypoxanthine, or xanthine?
What is the function of cAMP and cGMP in the cell?
What is the function of cAMP and cGMP in the cell?
What is the term for the synthesis of purine nucleotides from new building blocks?
What is the term for the synthesis of purine nucleotides from new building blocks?
What is the substrate for the synthesis of pyrimidine nucleotides de novo?
What is the substrate for the synthesis of pyrimidine nucleotides de novo?
What is the product of the synthesis of pyrimidine nucleotides de novo?
What is the product of the synthesis of pyrimidine nucleotides de novo?
Where is carbamoyl phosphate formed in urea synthesis?
Where is carbamoyl phosphate formed in urea synthesis?
What is the function of ATP synthetase II in pyrimidine nucleotide synthesis?
What is the function of ATP synthetase II in pyrimidine nucleotide synthesis?
What is the mechanism of action of sulfonamides in relation to paraaminobenzoic acid (PABA)?
What is the mechanism of action of sulfonamides in relation to paraaminobenzoic acid (PABA)?
What is the main difference between de novo synthesis and salvage reactions?
What is the main difference between de novo synthesis and salvage reactions?
What is the substrate used in the synthesis of purine nucleotides de novo?
What is the substrate used in the synthesis of purine nucleotides de novo?
What is the product of the synthesis of purine nucleotides de novo?
What is the product of the synthesis of purine nucleotides de novo?
What is the inhibitor of dihydrofolate reductase?
What is the inhibitor of dihydrofolate reductase?
What is the function of PRPP-synthetase?
What is the function of PRPP-synthetase?
What is the exception in the synthesis of pyrimidine nucleotides de novo?
What is the exception in the synthesis of pyrimidine nucleotides de novo?
Study Notes
Structure of Nucleotides
- Nucleotide = ester of phosphoric acid and a nucleoside
- Nucleoside = N-containing base + monosaccharide
- β-N-glycosidic bond between base and saccharide
- Nucleotide bases: aromatic heterocycles
- Purines: pyrimidine + imidazol ring
- Pyrimidines: pyrimidine ring
Classification of Nucleotides
- Purine nucleotides: contain adenine, guanine, hypoxanthine, or xanthine
- Pyrimidine nucleotides: contain cytosine, uracil, or thymine
- Ribonucleotides (saccharide = ribose)
- Deoxyribonucleotides (saccharide = deoxyribose)
Functions of Nucleotides
- Energetic metabolism: ATP = principal form of chemical energy available to cells (30 kJ/mol / splitting off phosphate)
- Monomeric units of RNA and DNA: nucleoside triphosphates
- Physiological mediators: cAMP, cGMP („second messengers“)
- Components of coenzymes: NAD+, NADP+, FAD, CoA
- Activated intermediates: UDP-Glc, CDP-choline, ethanolamine, diacylglycerol
- Allosteric effectors: regulation of key enzymes of metabolic pathways
Synthesis of Purine Nucleotides
- De novo synthesis: substrates = carbamoyl phosphate, aspartate, PRPP, methylene-THF (Gln, CO2, 2ATP)
- Synthesis occurs in the cytoplasm of many cells, mainly in the liver
- High consumption of energy (ATP)
- Important intermediates: 5'-phosphoribosylamine, inosine monophosphate (IMP)
- Products: nucleoside monophosphates (AMP, GMP)
Synthesis of Pyrimidine Nucleotides
- De novo synthesis: substrates = carbamoyl phosphate, aspartate, PRPP
- Important intermediates: orotic acid (pyrimidine derivative), orotidine monophosphate (OMP), uridine monophosphate (UMP)
- Products: cytidine triphosphate (from UTP), deoxythimidine monophosphate (from dUMP)
Regulation of Nucleotide Synthesis
- Regulatory enzyme activation: glutamine-PRPP amidotransferase (purines), ATP synthetase II (pyrimidines)
- Inhibition: IMP, GMP, AMP (allosteric inhibition), UTP
- Salvage reactions: synthesis from bases or nucleosides, less energy needed than for de novo synthesis, inhibits de novo synthesis
- Inhibitors for purine synthesis: sulfonamides, methotrexate, Trimethoprim
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Description
This quiz covers the structure and composition of purine and pyrimidine nucleotides, including their bases, nucleosides, and nucleotides. Learn about the differences between ribonucleosides and deoxyribonucleosides and how they form nucleotides.
