Purine and Pyrimidine Nucleotides

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Questions and Answers

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?

Ester bond

Phosphodiester bond

β-N-glycosidic bond (correct)

Anhydride bond

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?

Purine nucleotides Signup and view all the answers

What is the function of cAMP and cGMP in the cell?

As second messengers Signup and view all the answers

What is the term for the synthesis of purine nucleotides from new building blocks?

De novo synthesis Signup and view all the answers

What is the substrate for the synthesis of pyrimidine nucleotides de novo?

PRPP Signup and view all the answers

What is the product of the synthesis of pyrimidine nucleotides de novo?

Cytidine triphosphate Signup and view all the answers

Where is carbamoyl phosphate formed in urea synthesis?

Mitochondria of hepatocytes Signup and view all the answers

What is the function of ATP synthetase II in pyrimidine nucleotide synthesis?

Cytosolic inhibition Signup and view all the answers

What is the mechanism of action of sulfonamides in relation to paraaminobenzoic acid (PABA)?

Competitive antagonism Signup and view all the answers

What is the main difference between de novo synthesis and salvage reactions?

De novo synthesis requires more energy, while salvage reactions require less energy Signup and view all the answers

What is the substrate used in the synthesis of purine nucleotides de novo?

5-phosphoribosyl-1-diphosphate and amino acids Signup and view all the answers

What is the product of the synthesis of purine nucleotides de novo?

Nucleoside monophosphates (AMP, GMP) Signup and view all the answers

What is the inhibitor of dihydrofolate reductase?

Methotrexate Signup and view all the answers

What is the function of PRPP-synthetase?

To regulate nucleotide synthesis Signup and view all the answers

What is the exception in the synthesis of pyrimidine nucleotides de novo?

One enzyme is found in the mitochondria Signup and view all the answers

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.