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NUCLEIC ACIDS- Part 3
See all quizzes of NUCLEIC ACIDS- Part 3 here:
1 Ring closure of formimidoimidazole
carboxamide ribosyl-5-phosphate yields
the first purine nucleotide:
(A) AMP (B) IMP
(C) XMP (D) GMP
2. The cofactors required for synthesis of
adenylosuccinate are
(A) ATP, Mg++ (B) ADP
(C) GTP, Mg++ (D) GDP
3. Conversion of inosine monophosphate to
xanthine monophosphate is catalysed by
(A) IMP dehydrogenase
(B) Formyl transferase
(C) Xanthine-guanine phosphoribosyl transferase
(D) Adenine phosphoribosyl transferase
4. Phosphorylation of adenosine to AMP is
catalysed by
(A) Adenosine kinase
(B) Deoxycytidine kinase
(C) Adenylosuccinase
(D) Adenylosuccinate synthetase
5. The major determinant of the overall rate
of denovo purine nucleotide biosynthesis
is the concentration of
(A) 5-phosphoribosyl 1-pyrophosphate
(B) 5-phospho β-D-ribosylamine
(C) Glycinamide ribosyl-5-phosphate
(D) Formylglycinamide ribosyl-5-phosphate
6. An enzyme which acts as allosteric regulator
and sensitive to both phosphate
concentration and to the purine nucleotides
is
(A) PRPP synthetase
(B) PRPP glutamyl midotransferase
(C) HGPR Tase
(D) Formyl transferase
7. PRPP glutamyl amidotransferase, the first
enzyme uniquely committed to purine
synthesis is feed back inhibited by
(A) AMP (B) IMP
(C) XMP (D) CMP
8. Conversion of formylglycinamide ribosyl-
5-phosphate to formyl-glycinamide
ribosyl-5-phosphate is inhibited by
(A) Azaserine (B) Diazonorleucine
(C) 6-Mercaptopurine (D) Mycophenolic acid
9. In the biosynthesis of purine nucleotides
the AMP feed back regulates
(A) Adenylosuccinase
(B) Adenylosuccinate synthetase
(C) IMP dehydrogenase
(D) HGPR Tase
10. 6-Mercapto purine inhibits the conversion
of
(A) IMP→ XMP
(B) Ribose 5 phosphate → PRPP
(C) PRPP → 5-phospho → β -D-ribosylamine
(D) Glycinamide ribosyl 5-phosphate → formylglycinamide
ribosyl-5-phosphate
11. Purine biosynthesis is inhibited by
(A) Aminopterin (B) Tetracyclin
(C) Methotrexate (D) Chloramphenicol
12. Pyrimidine and purine nucleoside biosynthesis
share a common precursor:
(A) PRPP (B) Glycine
(C) Fumarate (D) Alanine
13. Pyrimidine biosynthesis begins with the
formation from glutamine, ATP and CO2,
of
(A) Carbamoyl aspartate
(B) Orotate
(C) Carbamoyl phosphate
(D) Dihydroorotate
14. The two nitrogen of the pyrimidine ring
are contributed by
(A) Ammonia and glycine
(B) Asparate and carbamoyl phosphate
(C) Glutamine and ammonia
(D) Aspartate and ammonia
15. A cofactor in the conversion of dihydroorotate
to orotic acid, catalysed by the
enzyme dihydroorotate dehydrogenase
is
(A) FAD (B) FMN
(C) NAD (D) NADP
16. The first true pyrimidine ribonucleotide
synthesized is
(A) UMP (B) UDP
(C) TMP (D) CTP
17. UDP and UTP are formed by phosphorylation
from
(A) AMP (B) ADP
(C) ATP (D) GTP
18. Reduction of ribonucleotide diphosphates
(NDPs) to their corresponding deoxy
ribonucleotide diphosphates (dNDPs)
involves
(A) FMN (B) FAD
(C) NAD (D) NADPH
19. Conversion of deoxyuridine monophosphate
to thymidine monophosphate is
catalysed by the enzyme:
(A) Ribonucleotide reductase
(B) Thymidylate synthetase
(C) CTP synthetase
(D) Orotidylic acid decarboxylase
20. d-UMP is converted to TMP by
(A) Methylation (B) Decarboxylation
(C) Reduction (D) Deamination
21. UTP is converted to CTP by
(A) Methylation (B) Isomerisation
(C) Amination (D) Reduction
22. Methotrexate blocks the synthesis of
thymidine monophosphate by inhibiting
the activity of the enzyme:
(A) Dihydrofolate reductase
(B) Orotate phosphoribosyl transferase
(C) Ribonucleotide reductase
(D) Dihydroorotase
23. A substrate for enzymes of pyrimidine
nucleotide biosynthesis is
(A) Allopurinol (B) Tetracylin
(C) Chloramphenicol (D) Puromycin
24. An enzyme of pyrimidine nucleotide biosynthesis
sensitive to allosteric regulation
is
(A) Aspartate transcarbamoylase
(B) Dihydroorotase
(C) Dihydroorotate dehydrogenase
(D) Orotidylic acid decarboxylase
25 An enzyme of pyrimidine nucleotides
biosynthesis regulated at the genetic
level by apparently coordinate repression
and derepression is
(A) Carbamoyl phosphate synthetase
(B) Dihydroorotate dehydrogenase
(C) Thymidine kinase
(D) Deoxycytidine kinase
26. The enzyme aspartate transcarbamoylase
of pyrimidine biosynthesis is inhibited
by
(A) ATP (B) ADP
(C) AMP (D) CTP
27. In humans end product of purine catabolism
is
(A) Uric acid (B) Urea
(C) Allantoin (D) Xanthine
28. In humans purine are catabolised to uric
acid due to lack of the enzyme:
(A) Urease (B) Uricase
(C) Xanthine oxidase (D) Guanase
29. In mammals other than higher primates
uric acid is converted by
(A) Oxidation to allantoin
(B) Reduction to ammonia
(C) Hydrolysis to ammonia
(D) Hydrolysis to allantoin
30. The correct sequence of the reactions of
catabolism of adenosine to uric acid is
(A) Adenosine→hypoxanthine→xanthine→uric
acid
(B) Adenosine→xanthine→inosine→uric acid
(C) Adenosine→inosine→hypoxanthine→ xanthine
uric acid
(D) Adenosine→xanthine→inosine→hypoxanthine
uric acid
