The synthesis and degradation of nucleotides

The immediate reducing power of ribonucleotide reductase is provided by: A. Thioredoxin B. Ferredoxin C. NADH D. Fe-S complex E. Cyt P450

A. Thioredoxin

All of characteristics of Lesch-Nyham syndrome EXCEPT: A. Gouty arthritis B. Severe malfunctions of the nervous system C. Complete deficiency in HGPRT activity D. Congenital, recessive, sex-linked trait anifested only in males E. All are true

All are true

The coenzyme for two single carbon additions in purine biosynthesis is: A. THF B. Biotin C. SAM D. TPP E. None

A. THF

Allopurinol is an analog of _________ that tightly binds to ____________ and prevents ____________ formation. A. Hypoxanthine; xanthine oxidase; uric acid B. Guanine; guanine deaminase; xanthine C. Inosine; xanthien oxidase; xanthine D. Hypoxanthine; guanine deaminase; xanthine E. None

A. Hypoxanthine; xanthine oxidase; uric acid

Thymidylate synthase synthesizes dTMP from _______________ by _______________ utilizing the coenzyme _________. A. -dCTP; carboxylation; biotin B. -dUMP; methylation; THF C. -dCMP; methylation; THF D. -dGMP; Phosphorylation; ATP E. -dUMP; phosphorylation; ATP

B. -dUMP; methylation; THF Thymidylate synthase synthesizes dTMP from dUMP by methylation utilizing the coenzyme THF.

Which of the following statements explains why methotrexate is effective as a cancer chemotherapeutic? A. It serves as an analog of p-aminobenzoic acid and block bacterial synthesis of folate B. Acts as an inhibitor of dihydrofolate reductase, thus preventing production of tetrahydrofolate C. It acts as a suicide substrate for the enzyme dihydropteroate synthetase D. Prevents the conversation of N5, N10-methenyl THF to N10-formyl THF which is required in 2 steps of the purine synthesis pathway E. Both B and D are correct

B. Acts as an inhibitor of dihydrofolate reductase, thus preventing production of tetrahydrofolate

Which of the following serves as one of the nitrogen sources for the pyrimidine ring? A. Glutamate B. Carbamoyl phosphate C. Asparagine D. Glycine E. None of the above

B. Carbamoyl phosphate

Which form of the folate coenzyme is directly involved in the synthesis of the purine ring? A. N5-N10-methenyl THF B. N10-formyl THF C. N5-formyl THF D. Tetrahydrofolate E. Dihydrofolate

B. N10-formyl THF

All are substrate of carbamoyl phosphate synthetase II (CPS-II) except: A. H20 B. NH4+ C. HCO3- D. Glutamine E. 2ATP

B. NH4+

Which of the following is the mechanism of action of 5-fluorouracil? A. Competitive inhibitor of dihydrofolate reductase B. Suicide substrate for thymidylate synthase C. Competitive inhibitor of ribonucleotide reductase D. Non-competitive inhibitor of thioredoxin reductase E. None of the above

B. Suicide substrate for thymidylate synthase

Thymine nucleotides are not synthesized directly by cells but indirectly from other pyrimidine deoxy ribonucleotides. All of the following statements regarding thymine nucleotide synthesis are true EXCEPT: A. DUMP is the immediate precursor for dTMP B. The action dUTPase allows dUTP to serve as a substrate in DNA synthesis C. Thymidylate synthase catalyzes the formation of dTMP from dUMP. D. The methyl donor in the reaction of dTMP is N5,N10-methylene-THF E. THF is used as a cofactor

B. The action of dUTPase allows dUTP to serve as a substrate in DNA synthesis.

What is the common product of purine catabolism? A. Xanthine B. Uric acid C. Inosine D. Hypoxanthine E. Xanthosine

B. Uric acid

The reaction, base + PRPP --> nucleoside-5-phosphate + PPi is catalyzed by the enzyme; A. Nucleotide diphosphate kinase B. Phosphoribosyltransferase C. Ribose-5-phosphate pyrophosphokinase D. Adenylate kinase E. GMP synthetase

B. phosphoribosyltransferase

What type of reaction gives UMP from OMP? A. Reduction B. Decarboxylation C. Oxidation D. Condensation E. Hydrolysis

B.Decarboxylation

Which of the following is a source of 2 carbon atoms of the purine ring system? A. Aspartate B. Carbon dioxide C. Glycine D. Glutamine E. Glutamic acid

C. Glycine

All are characteristics of xanthine oxidase EXCEPT: A. Present in large amounts in liver, intestinal mucosa and milk. B. Use molecular oxygen and produces H2O2 C. Involved in production of urea D. Possesses an ETC with FAD, Fe-S cluster and molybdenum cofactor E. All are true

C. Involved in the production of urea

Which of the following statements explains why allopurinol is able to prevent gout? A. It binds to uric acid thus preventing the formation of uric acid crystals B. It as acts as a diuretic to increase the elimination of uric acid C. It inhibits the production of uric acid and allows for the more highly soluble xanthine and hypoxanthine to be excreted from the body D. It stimulates the purine salvage pathway E. None

C. It inhibits the production of uric acid and allows for more highly soluble xanthine and hypoxanthine to be excreted from the body

What is the importance of the purine nucleoside cycle? A. It participates in the conversion of purines into pyrimidines B. It generates fumarate, which inhibits the formation of AMP from IMP C. It provides fumarate as an anaploretic enhancement of the citric acid cycle D. It inhibits the citric acid cycle in skeletal muscles E. It is used in energy metabolism in the liver.

C. It provides fumarate as an anaploretic enhancement of the citric acid cycle

What is the function of phosphoribosyltransferase? A. They are involved in the reversible reactions of purine salvage B. They mediate the degradation of AMP C. They are central to the re-synthesis of nucleotides from bases in salvage reactions D. They mediate the degradation of IMP E. They are competitive inhibitors employed in the salvage of purine nucleotides

C. They are central to the re-synthesis of nucleotides from bases in salvage reactions

The fate of IMP is regulated by relative levels of ___________ and _________; and energy to drive AMP synthesis is provided by ____________, and energy for GMP synthesis by ________________. A. IMP; PRPP; ATP; GTP B. PRPP; ATP; ATP; GTP C. AMP; ATP; GTP; ATP D. AMP; GMP; GTP; ATP E. IMP; GMP; ATP; GTP

D. AMP; GMP; GTP; ATP

About 30% of severe combined immunodeficiency syndrome (SCIDS) patients suffer from a deficiency in the activity of the enzyme ____________ that is a _______________ dependent enzyme and _____________ deficiency can also lead to reduced immune function. A. HGPRT; Ca; Ca B. Nucleosides; Ca; Ca C. Nucleoside phosphorylase; Pi; Pi D. Adenosine deaminase; Zn; Zn E. None are true

D. Adenosine deaminase; Zn; Zn

Many _____________ and ______________ are inhibitors of purine and pyrimidine biosynthesis. A. Eicoanoids; aspirin B. NSAIDs; antibiotics C. Antibiotics; eicosanoids D. Anticancer drugs; antibiotics E. Anticancer drugs; eicosanoids

D. Anti cancer drugs; antibiotics

Which of the following states regarding the activity of ribonucleotide reductase is correct? A. The overall activity of the enzyme is inhibited by high levels of ATP B. Binding of ATP to the specificity site increases the use of GDP as a substrate C. Binding of dGTP to the specificity site increases the use of CDP as a substrate D. Binding of dTTP to the specificity site inhibits the use of UDP as a substrate E. None

D. Binding of dTTP to the specificity site inhibits the use of UDP as a substrate

Adenylosuccinase (adenylosuccinate lyase) catalyzes the reaction to remove ___________ after __________ has formed an amide with a carbonyl group in purine biosynthesis. A. Succinate; glutamate B. Succinate; aspartate C. Fumarate; alanine D. Fumarate; aspartate E. Alpha-ketoglutarate

D. Fumarate; aspartate

Which of the following would cause an increase in the conversion of IMP to GMP? A. High levels of CMP B. High levels of dTTP C. High levels of UMP D. High levels of AMP E. None of the above

D. High levels of AMP

What is the limiting substance in the biosynthesis of Purines? A. Ribose-5-phosphate B. 5-phosphoribosyl-B-amine C. Formylglycinamidine ribonucleotide D. 5-phosphoribosyl-alpha-pyrophosphate (PRPP) E. Alpha-D-ribose-5-phosphate

D. PRPP

Glutamine phosphoribosyl pyrophosphate amidotransferase catalyzes step 2 in the biosynthesis of purines. Which of the following is a true statement regarding the regulation of this enzyme? A. It is accelerated by an input of ATP or GTP B. It is sensitive to activation by azaserine C. It is accelerated by an input of AMP or GMP D. The G series of nucleotides as well as the adenine nucleotides act as competitive inhibitors. E. It is subject to feed-forward activation by ADP.

D. The G series of nucleotides as well as the adenine nucleotides act as competitive inhibitors

All of the following are true concerning the regulation of the purine biosynthetic pathway EXCEPT: A. ATP is the energy source for AMP synthesis B. ADP and GDP are feedback inhibitors of ribose-5-phosphate pyrophosphokinase. C. "A" and "C" nucleotides allosterically inhibit glutamine phosphoribosyl pyrophosphate amindotransferase (Gln:PRPP amindotransferase) D. The rate of IMP formation is dependent on the levels of the adenine and guanine nucleotides produced. E. PRPP completely inhibits the enzyme Gln:PRPP amindotransferase

E. PRPP completely inhibits the enzyme Gln:PRPP amidotransferase *PRPP activates Gln-PRPP amidotransferase

All of the following statements about nucleotides are true except: A. They are produced by all organisms. B. The rate of proliferation of a cell can determine the amount of DNA and RNA synthesizd per unit of time. C. Uridine nucleotide derivatives of carbohydrates are common intermediates in cellular transformation of carbohydrates. D. Many coenzymes are derivatives of nucleotides. E. The nitrogenous bases serve as energy sources.

E. The nitrogenous bases serve as energy sources.