Exam 18: Nucleotide Metabolism

Which are purines?

5-methylcytidine is a common modified base in mammalian DNA that plays roles in ________.

The major end product of purine degradation in humans is

Which is not a direct precursor of pyrimidines in their de novo biosynthesis?

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

Humans and other terrestrial organisms lack the enzyme urease which,if present,would cause a toxic level of ammonia.

Although dUTP can be synthesized from UDP and ATP,it is not accidentally incorporated into DNA in place of ________ because it is rapidly hydrolyzed

Allopurinol may be used to treat gout due to an excess of uric acid production because it can be converted to oxypurinol by ________,and oxypurinol strongly inhibits ________.

The purine ring system is shown below.What is the source of the C-6 atom during de novo biosynthesis of purines?

dUTP is not a direct precursor of dTTP because ________.

Which enzyme catalyzes the step in purine nucleotide biosynthesis that is the principal site of regulation for the pathway?

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

In pyrimidine nucleotide biosynthesis orotate is the molecule that displaces the pyrophosphate group on PRPP.

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

PRPP synthetase is inhibited by several purine ribonucleotides but only at concentrations lower than those usually found in the cell so there remains a supply for other cell reactions.

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

The first nucleotide product in the de novo biosynthetic pathway of purines is

Virtually all organisms and tissues can synthesize nucleotides.

The pyrimidine ring system is shown below.What is the source of the N-3 during the de novo biosynthesis of pyrimidines?

During de novo biosynthesis of the purine nucleotides,the purine ring is first formed as a free base before being attached to the ribose 5-phosphate moiety.