BIOCHEMISTRY
51. Histamine is formed from histidine by the enzyme histidine decarboxylase in the presence of
(A) NAD (B) FMN
(C) HS-CoA (D) B6-PO4
52. Infantile convulsions due to lesser formation of gamma amino butyric acid from glutamic acid is seen in the deficiency of
(A) Glutamate-dehydrogenase
(B) Pyridoxine
(C) Folic acid
(D) Thiamin
53. Which of the following amino acids produce a vasoconstrictor on decarboxylation?
(A) Histidine
(B) Tyrosine
(C) Threonine
(D) Arginine
54. The degradation of RNA by pancreatic ribonuclease produces
(A) Nucleoside 2-Phosphates
(B) Nucleoside 5′-phosphates
(C) Oligonucleosides
(D) Nucleoside 3′-phosphate and oligonucleotide
55. Intestinal nucleosidases act on nucleosides and produce
(A) Purine base only
(B) Phosphate only
(C) Sugar only
(D) Purine or pyrimidine bases and sugars
56. In purine biosynthesis carbon atoms at 4 and 5 position and N at 7 position are contributed by
(A) Glycine
(B) Glutamine
(C) Alanine
(D) Threonine
57. N10-formyl and N5N10-methenyl tetrahydrofolate contributes purine carbon atoms at position
(A) 4 and 6
(B) 4 and 5
(C) 5 and 6
(D) 2 and 8
58. In purine nucleus nitrogen atom at 1 position is derived from
(A) Aspartate (B) Glutamate
(C) Glycine (D) Alanine
59. The key substance in the synthesis of purine, phosphoribosyl pyrophosphate is formed by
(A) α-D-ribose 5-phosphate
(B) 5-phospho β-D-ribosylamine
(C) D-ribose
(D) Deoxyribose
60. In purine biosynthesis ring closure in the molecule formyl glycinamide ribosyl-5- phosphate requires the cofactors:
(A) ADP
(B) NAD
(C) FAD
(D) ATP and Mg++
61. Ring closure of formimidoimidazole carboxamide ribosyl-5-phosphate yields the first purine nucleotide:
(A) AMP (B) IMP
(C) XMP (D) GMP
62. The cofactors required for synthesis of adenylosuccinate are
(A) ATP, Mg++
(B) ADP
(C) GTP, Mg++
(D) GDP
63. 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
64. Phosphorylation of adenosine to AMP is catalysed by
(A) Adenosine kinase
(B) Deoxycytidine kinase
(C) Adenylosuccinase
(D) Adenylosuccinate synthetase
65. 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
66. 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
67. PRPP glutamyl amidotransferase, the first enzyme uniquely committed to purine synthesis is feedback inhibited by
(A) AMP
(B) IMP
(C) XMP
(D) CMP
68. 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
69. in the biosynthesis of purine nucleotides The AMP feedback regulates
(A) Adenylosuccinase
(B) Adenylosuccinate synthetase
(C) IMP dehydrogenase
(D) HGPR Tase
70. 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
71. Purine biosynthesis is inhibited by
(A) Aminopterin
(B) Tetracyclin
(C) Methotrexate
(D) Chloramphenicol
72. Pyrimidine and purine nucleoside biosynthesis share a common precursor:
(A) PRPP (B) Glycine
(C) Fumarate (D) Alanine
73. Pyrimidine biosynthesis begins with the Formation from glutamine, ATP and CO2, Of
(A) Carbamoyl aspartate
(B) Orotate
(C) Carbamoyl phosphate
(D) Dihydroorotate
74. 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
75. A cofactor in the conversion of dihydroorotate to orotic acid, catalysed by theenzyme dihydroorotate dehydrogenase is
(A) FAD (B) FMN
(C) NAD (D) NADP
76. The first true pyrimidine ribonucleotide Synthesized is
(A) UMP
(B) UDP
(C) TMP
(D) CTP
77. UDP and UTP are formed by phosphorylation from
(A) AMP
(B) ADP
(C) ATP
(D) GTP
78. Reduction of ribonucleotide diphosphates (NDPs) to their corresponding deoxy ribonucleotide diphosphates (dNDPs) involves
(A) FMN
(B) FAD
(C) NAD
(D) NADPH
79. 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
80. d-UMP is converted to TMP by
(A) Methylation
(B) Decarboxylation
(C) Reduction
(D) Deamination
81. UTP is converted to CTP by
(A) Methylation
(B) Isomerisation
(C) Amination
(D) Reduction
82. 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
83. A substrate for enzymes of pyrimidine nucleotide biosynthesis is
(A) Allopurinol
(B) Tetracylin
(C) Chloramphenicol
(D) Puromycin
84. An enzyme of pyrimidine nucleotide biosynthesis sensitive to allosteric regulation is
(A) Aspartate transcarbamoylase
(B) Dihydroorotase
(C) Dihydroorotate dehydrogenase
(D) Orotidylic acid decarboxylase
85 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
86. The enzyme aspartate transcarbamoylase of pyrimidine biosynthesis is inhibited by
(A) ATP
(B) ADP
(C) AMP
(D) CTP
87. In humans end product of purine catabolism is
(A) Uric acid (B) Urea
(C) Allantoin (D) Xanthine
88. in human’s purine are catabolised to uric acid due to lack of the enzyme:
(A) Urease
(B) Uricase
(C) Xanthine oxidase
(D) Guanase
89. 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
90. 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
91. Gout is a metabolic disorder of catabolism of
(A) Pyrimidine
(B) Purine
(C) Alanine
(D) Phenylalanine
92. Gout is characterized by increased plasma levels of
(A) Urea (B) Uric acid
(C) Creatine (D) Creatinine
93. Lesch-Nyhan syndrome, the sex linked recessive disorder is due to the lack of the enzyme:
(A) Hypoxanthine-guanine phosphoribosyl Transferse
(B) Xanthine oxidase
(C) Adenine phosphoribosyl transferase
(D) Adenosine Deaminase
94. Lesch-Nyhan syndrome, the sex linked, recessive absence of HGPRTase, may lead to
(A) Compulsive self-destructive behaviour with elevated levels of urate in serum
(B) Hypouricemia due to liver damage
(C) Failure to thrive and megaloblastic anemia
(D) Protein intolerance and hepatic encephalopathy
95. The major catabolic product of pyrimidines in human is
(A) β-Alanine
(B) Urea
(C) Uric acid
(D) Guanine
96. Orotic aciduria type I reflects the deficiency of enzymes:
(A) Orotate phosphoribosyl transferase and Orotidylate decarboxylase
(B) Dihydroorotate dehydrogenase
(C) Dihydroorotase
(D) Carbamoyl phosphate synthetase
97. Orotic aciduria type II reflects the deficiency of the enzyme:
(A) Orotate phosphoribosyl transferase
(B) Orotidylate decarboxylase
(C) Dihydroorotase
(D) Dihydroorotate dehydrogenase
98. An autosomal recessive disorder, xanthinuria is due to deficiency of the enzymes:
(A) Adenosine deaminase
(B) Xanthine oxidase
(C) HGPRTase
(D) Transaminase
99. Enzymic deficiency in βββ-aminoisobutyric aciduria is
(A) Adenosine deaminase
(B) Xanthine oxidase
(C) Orotidylate decarboxylase
(D) Transaminase
100. Polysomes lack in
(A) DNA
(B) mRNA
(C) rRNA
(D) tRNA
