Q-61. The following hormone does not have any intracellular receptor:
a) Vitamin D3
b) Cortisone
c) Adrenaline
d) Thyroxin
Answer: Adrenaline
Explanation:
Intracellular receptor:
Cytoplasmic receptors:
Glucocorticoids
Mineralocorticoids
Estrogen
Progestin
Vitamin D
Nuclear receptors:
Thyroid hormone
Q-62. Accumulation of sphingomyelin in phagocytic cells is feature of:
a) Gaucher Disease
b) Niemann Pick Disease
c) Down Syndrome
d) Tay Sachs Disease
Answer: Niemann Pick Disease
Explanation:
Niemann-Pick disease (NPD) is a lipid storage disorder that results from the deficiency of a lysosomal enzyme, acid Sphingomyelinase.
The diagnosis of Niemann-Pick disease (NPD) is confirmed with measurement of enzyme activity in peripheral white blood cells or in cultured fibroblasts.
Q-63. Basic amino acids are
a) Aspartate and glutamate
b) Serine and glycine
c) Lysine and arginine
d) None of the above
Answer: Lysine and arginine
Explanation:
Amino Acid with Side Chains Containing Basic Groups: Arginine, Lysine, Histidine
Amino Acid with Side Chains Containing Acidic Groups or Their Amides: Aspartic Acid, Asparagine, Glutamic Acids and Glutamine
Q-64. Amino acid with dissociation constant closest to physiological pH is
a) Serine
b) Histidine
c) Threonine
d) Proline
Answer: Histidine
Explanation:
Histidine plays unique roles in enzymatic catalysis. The pK of its imidazole proton permits it to function at neutral pH or physiological pH as either a base or an acid catalyst.
Q-65. Sources of the nitrogen in urea cycle are
a) Aspartate and ammonia
b) Glutamate and ammonia
c) Arginine and ammonia
d) Uric acid
Answer: Aspartate and ammonia
Explanation:
Urea cycle occurs in liver and urea is produced. Urea is transported in the blood to kidneys for excretion in the urine.
The first two reactions leading to the synthesis of urea occur in the mitochondria, whereas the remaining cycle enzymes are located in cytosol.
Important points:
Synthesis of urea is irreversible.
Carbamoyl phosphate synthetase-I is rate limiting step in the urea cycle.
N-acetyl-glutamate is essential activator for carbamoyl phosphate synthetase-I.
Synthesis of one mol of urea requires 3 mol of ATP and one mol of ammonium ion.
First nitrogen of urea is supplied by free ammonia and second nitrogen is supplied by aspartate.
Q-66. If urine sample darkens on standing the most likely condition is
a) Phenyl-ketonuria
b) Alkaptonuria
c) Maple syrup disease
d) Tyrosinemia
Answer: Alkaptonuria
Explanation:
Alkaptonuria is autosomal recessive disease due to deficiency of Homogentisate oxidase.
The urine darkens on exposure to air due to oxidation of excreted Homogentisate.
Late in the disease, there is arthritis and connective tissue pigmentation (Ochronosis) due to oxidation of Homogentisate to benzoquinone acetate which polymerizes and binds to connective tissue.
Q-67. A baby presents with refusal to feed, skin lesions, seizures, ketosis, organic acids in urine with normal ammonia; likely diagnosis is
a) Propionic aciduria
b) Multiple carboxylase deficiency
c) Maple syrup urine disease
d) Urea cycle enzyme deficiency
Answer: Multiple carboxylase deficiency
Explanation:
Biotin is a coenzyme for pyruvate carboxylase, propionyl-CoA carboxylase, beta-methylcrotonyl-CoA carboxylase, and acetyl-CoA carboxylase.
Multiple carboxylase deficiency is one of many metabolic disorders that occur in the absence of the coenzyme activity of biotin.
Presentation of multiple carboxylase deficiency:
Intractable seizures, hypotonia, spastic para-paresis, unexplained visual loss or visual field loss, unexplained sensorineural hearing loss
Loss of hair color (Achromotrichia), loss of hair (alopecia), and an eczematous, scaly peri-oral/facial rash
Metabolic keto-acidosis or organic acidosis
Immunologic dysfunction
Failure to thrive
Important point:
Normal levels of ammonia rule out urea cycle enzyme deficiency.
Q-68. Force not acting in an enzyme substrate complex
a) Electrostatic
b) Covalent
c) Van der Waals
d) Hydrogen
Answer: Van der Waals
Explanation:
Mechanisms to facilitate catalysis:
Catalysis by proximity
Acid-Base catalysis
Catalysis by strain
Covalent catalysis
Force acting in an enzyme substrate complex:
Hydrogen and ionic binding (Electrostatic)
Hydrophobic interactions
Covalent bonding
Q-69. Cellular oxidation is inhibited by
a) Cyanide
b) Carbon dioxide
c) Chocolate
d) Carbonated beverages
Answer: Cyanide
Explanation:
Site specific inhibitors of electron transport prevent the passage of electrons by binding to a component of chain, blocking the oxidation and reduction reaction.
Because electron transport and oxidative phosphorylation are tightly coupled, site specific inhibition of electron transport chain also inhibits ATP synthesis.
Site Specific Inhibitors of Electron Transport:
Amytal/ Rotenone:
FMN> CoQ
Antimycin A:
Cytochrome b> Cytochrome c
CN-/CO/Sodium azide:
Cytochrome c oxidase (Cytochrome a + a3)> O2
Q-70. Triple bonds are found between which base pairs
a) A-T
b) C-G
c) A-G
d) C-T
Answer: C-G
Explanation:
Triple hydrogen bonds are found between guanine and cytosine.
Double hydrogen bonds are found between adenine and thymidine.