Exam 18: Nucleotide Metabolism

Xanthine oxidase catalyzes the formation of .

The purine ring system is shown below. What is the source of the carbon atoms 2 and 8 during de novo biosynthesis of purines?

Which is a method by which the synthesis of AMP or GMP is regulated?

Channeling is an important process in the biosynthesis of pyrimidine nucleotides in mammals.

The pathway for the synthesis of IMP releases considerable energy and is an important source of ATP.

Pigs excrete guanine rather that further catabolizing it because .

In birds and reptiles, purine nucleotides and surplus nitrogen from amino acid catabolism is disposed of in the form of while humans form that, as well as in nitrogenous waste.

The pyrimidine ring system is shown below. What is the source of the C-2 during the de novo biosynthesis of pyrimidines?

In prokaryotes, carbamoyl phosphate is an intermediate in the de novo biosynthesis of pyrimidine nucleotides.

Substrates for reduction to form deoxyribonucleotides are

Carbamoyl phosphate synthetase I is located in the in eukaryotes and uses as a nitrogen source.

Which catalytic site is not contained in the eukaryotic multifunctional protein dihydroorotate synthase?

In eukaryotes all enzymes for the biosynthesis of the pyrimidine nucleotides occur exclusively in the cytosol.

dCMP, dGMP, dAMP and dTMP are substrates for a reductase that phosphorylates them to the triphosphate levels for incorporation into DNA.

Ribonucleotides are produced from oxidation of the deoxyribonucleotides at the 2ʹ carbon atom.

High levels of will almost totally inhibit ATCase.

In the de novo synthesis of the deoxyribonucleotides, the deoxy form of PRPP is used in place of the PRPP used in the synthesis of the ribonucleotides.

dUTP is not a direct precursor of dTTP because .

is a precursor for the de novo synthesis of AMP and GMP.

The coenzyme biotin is required for the carboxylation of aminoimidazole ribonucleotide (AIR) during the de novo synthesis of IMP by the enzyme AIR carboxylase.