Q-71. Which of the following RNA has abnormal purine bases?
a) t-RNA
b) m-RNA
c) r-RNA
d) 16S RNA
Answer: t-RNA
Explanation:
Transfer-RNAs, the smallest of three major species of RNA molecules, have between 74 and 95 nucleotide residues.
Transfer-RNAs contain unusual bases such as pseudo-uracil and have extensive intra-chain base pairing.
Q-72. False regarding gout is
a) Due to increased metabolism of pyrimidines
b) Due to increased metabolism of purines
c) Uric acid levels may not be elevated
d) Has a predilection for the great toe
Answer: Due to increased metabolism of pyrimidines
Explanation:
Gout is a metabolic disorder of purine catabolism. Uric acid is formed from purine nucleosides produced by the breakdown of nucleic acids and other nucleotides e.g. ATP and in humans is the end product of purine catabolism.
Uric acid exhibits anti-oxidant properties.
Q-73. All to the following statement are true regarding lipoproteins except
a) VLDL transports endogenous lipids
b) LDL transports lipids to the tissues
c) Increased blood cholesterol is associated with increased LDL receptors
d) Increased HDL is associated with decreased risk of coronary disease
Answer: Increased blood cholesterol is associated with increased LDL receptors
Explanation:
VLDL transports endogenous lipids.
LDL transports lipids to the tissues.
Increased HDL is associated with decreased risk of coronary disease.
Important points:
HDL is synthesized and secreted from both liver and intestine.
However, apo-C and apo-E are synthesized in the liver and transferred from liver HDL to intestinal HDL when the later enters the plasma.
A major function of HDL is act as a repository for apo-C and apo-E required in the metabolism of chylomicrons and VLDL.
Reverse the cholesterol transport to liver for excretion via bile
HDL-2 concentrations are inversely related to the incidence of atherosclerosis.
Q-74. A Destitute woman is admitted to the hospital with altered sensorium and dehydration. Urine analysis shows mild proteinuria and no sugar. What other test would be desirable?
a) Fouchet’s test
b) Rothera’s
c) Hays
d) Benedicts
Answer: Rothera’s
Explanation:
A Destitute woman is admitted to the hospital with altered sensorium and dehydration. Urine analysis shows mild proteinuria and no sugar. Diagnosis is starvation ketosis.
Ketoacidosis is the term used for metabolic acidosis associated with an accumulation of ketone bodies.
The most common cause of keto-acidosis is diabetic keto-acidosis. Two other causes are fasting ketosis and alcoholic keto-acidosis.
Important point:
Rothera’s test: Method of testing urine for the presence of acetone or acetoacetic acid
Q-75. Which of these fatty acids is found exclusively in breast milk?
a) Linoleate
b) Linolenic
c) Palmitic
d) Docosahexaenoic acid
Answer: Docosahexaenoic acid
Explanation:
Docosahexaenoic acid (DHA) which is synthesized to a limited extent from alpha Linolenic acid or obtained directly from fish oils is present in high concentration in retina, cerebral cortex, testis, and sperm.
DHA is particularly needed for development of the brain and retina and is supplied via the placenta and milk.
Patients with retinitis pigmentosa are reported to have low blood levels of DHA.
Q-76. Blood is not a Newtonian fluid because
a) Viscosity does not changing with velocity
b) Viscosity changes with velocity
c) Density does not change with velocity
d) Density changes with velocity
Answer: Viscosity changes with velocity
Explanation:
A Newtonian liquid is one in which the viscosity, at fixed temperature and pressure, is independent of the shear stress or viscosity is constant regardless of the flow velocity.
Thus, a non-Newtonian liquid is one in which the viscosity depends on shear stress or viscosity changes with velocity.
Blood is not a Newtonian fluid. Viscosity of blood changes with velocity.
Q-77. Elasticity of the corneal layer of skin is due to the presence of
a) Cysteine
b) Lysine
c) Keratin
d) Histidine
Answer: Keratin
Explanation:
The stratum corneum, the fifth, outermost layer is thick with rows of dead cells. These cells contain soft keratin, which keeps the skin elastic and protects underlying cells from drying out. Keratin is a family of fibrous structural proteins.
In addition to intra- and intermolecular hydrogen bonds, keratins have large amounts of the sulfur-containing amino acid cysteine, required for the disulfide bridges that confer additional strength and rigidity.
Q-78. All enzymes are not proteins; this statement is justified by
a) All enzymes do not following the Michaelis Menten hypothesis
b) RNAs act as ribozymes
c) Antibodies take part in the catalysis of many reactions
d) Metals are involved in attachment to enzymes and catalysts
Answer: RNAs act as ribozymes
Explanation:
An Abzyme is a monoclonal antibody with catalytic activity.
Ribozymes are RNA molecules with catalytic activity. These generally involve trans-esterification reactions, and most are concerned with RNA metabolism (Splicing and endo-ribonuclease)
Ribozyme also performs the peptidyl transferase activity.
Important points:
The Peptidyl transferase is an amino-acyl-transferase as well as the primary enzymatic function of the ribosome, which forms peptide bonds between adjacent amino acids using t-RNAs during the translation process of protein biosynthesis.
Peptidyl transferase activity is carried out by the ribosome. Peptidyl transferase activity is not mediated by any ribosomal proteins but by ribosomal RNA (rRNA), a ribozyme.
Peptidyl transferase activity is intrinsic to the 23S r-RNA found in the 60S ribosomal subunit.
Q-79. Enzymes mediating transfer of one molecule to another are
a) Transferases
b) Oxidases
c) Lyases
d) Peptidases
Answer: Transferases
Explanation:
Enzymes are grouped into six classes:
Oxidoreductases (catalyze oxidations and reductions) e.g. Tyrosinase
Transferases (catalyze transfer of moieties such as glycosyl, methyl, or phosphoryl groups) e.g. Hexokinase
Hydrolases (catalyze hydrolytic cleavage of C-C, C-O, C-N, and other bonds)
Lyases (catalyze cleavage of C-C, C-O, C-N and other bonds by atom elimination, leaving double bonds) e.g. Fumarase
Isomerases (catalyze geometric or structural changes within a molecule)
Ligases (catalyze the joining together of two molecules coupled to the hydrolysis of ATP) e.g. glutamine synthetase
Q-80. In which of the following reactions is magnesium required
a) ATPase
b) Dismutase
c) Phosphatase
d) Aldolase
Answer: Phosphatase
Explanation:
Mg++ is required in:
Phosphatase
Kinase
Ribonuclease
Peptidase
Ca carboxylase
Adenyl cyclase
Trans-ketolase