Purine and Pyrimidine Metabolism

Fill-in-the-blank practice flashcards covering de novo and salvage pathways, catabolism, and associated clinical disorders of purine and pyrimidine metabolism based on lecture notes.

In de novo nucleotide synthesis, __________ pathways recycle free bases and nucleosides released from nucleic acid breakdown.

salvage

In the pyrimidine ring, atoms $N_1$, $C_4$, $C_5$, and $C_6$ are derived from __________.

aspartate

In de novo pyrimidine biosynthesis, the atom $C_2$ is derived from __________.

$$CO_2$$

In de novo pyrimidine biosynthesis, the six-membered ring is synthesized __________ it is attached to ribose 5-phosphate.

before

The formation of N-Carbamoylaspartate from aspartate and carbamoyl phosphate is catalyzed by __________.

aspartate transcarbamoylase

The enzyme dihydroorotase removes water to close the ring during the formation of __________.

L-dihydroorotate

The oxidation of L-dihydroorotate to orotate is catalyzed by dihydroorotate dehydrogenase and reduces __________ to $NADH + H^+$.

$$NAD^+$$

Orotate phosphoribosyl-transferase transfers the 5-phosphoribosyl group from __________ to orotate to form orotidylate.

PRPP

The first pyrimidine nucleotide synthesized in the de novo pathway is __________.

UMP

Cytidylate synthetase converts UTP into CTP using ATP and the amino acid __________ as an amino donor.

glutamine

The catabolism of uracil and cytosine produces $CO_2$, $NH_3$, and __________.

$$\beta\text{-alanine}$$

The catabolism of thymine produces $CO_2$, $NH_3$, and __________.

$$\beta\text{-aminoisobutyrate}$$

Unlike pyrimidines, the purine ring is constructed directly on __________.

ribose-5'-phosphate

In the purine ring, atoms $C_2$ and $C_8$ are derived from __________.

formate

In purine biosynthesis, atoms $C_4$, $C_5$, and $N_7$ are all provided by the amino acid __________.

glycine

The conversion of PRPP to 5'-phospho-$\beta$-D-ribosylamine is catalyzed by __________.

glutamine-PRPP amidotransferase

The common purine nucleotide precursor from which both AMP and GMP are synthesized is __________.

inosinate

The synthesis of AMP from IMP requires aspartate and the energy source __________.

GTP

The conversion of XMP to GMP is catalyzed by XMP-glutamine amidotransferase and requires glutamine and __________.

ATP

The enzyme HGPRTase catalyzes the one-step salvage of hypoxanthine and guanine using __________ as the donor of the ribosyl moiety.

PRPP

The final purine catabolism end product excreted by primates, birds, reptiles, and insects is __________.

uric acid

Most mammals degrade uric acid into __________ using the enzyme urate oxidase.

allantoin

Gout is characterized by hyperuricemia and the deposition of sodium monourate crystals forming structures known as __________.

tophi

Allopurinol lowers serum uric acid levels by acting as a competitive inhibitor of the enzyme __________.

xanthine oxidase

Lesch-Nyhan syndrome is an X-linked recessive disorder caused by a genetic lack of __________ activity.

hypoxanthine-guanine phosphoribosyltransferase

Adenosine deaminase deficiency is an autosomal recessive disorder that results in a severe deficiency of both __________ cells.

T and B

Type I orotic aciduria is an autosomal recessive disorder characterized by a lack of activity in orotate phosphoribosyltransferase and __________.

OMP decarboxylase

The chemotherapeutic drug Fluorouracil acts as an inhibitor of the enzyme __________.

thymidylate synthase

Methotrexate and Aminopterin inhibit the enzyme __________ to block thymine synthesis.

dihydrofolate reductase

In von-Gierke's disease, a deficiency in glucose-6-phosphatase leads to increased pentose formation in the __________ pathway.

HMP