Q-101. The primary role of chaperones is to help in
a) Protein synthesis
b) Protein degradation
c) Protein de-naturation
d) Protein folding
Answer: Protein folding
Explanation:
Chaperone proteins participate in the folding of over half of mammalian proteins.
The hsp 70 (70-kDa heat shock protein) family of chaperones binds short sequences of hydrophobic amino acids in newly synthesized polypeptides, shielding them from solvent.
Chaperones prevent aggregation, thus providing an opportunity for the formation of appropriate secondary structural elements and their subsequent coalescence into a molten globule.
Hsp60 acts later in the folding process, often together with an hsp 70 chaperone.
Q-102. The main enzyme responsible for activation of xenobiotics is
a) Cytochrome P-450
b) Glutathione S-transferase
c) NADPH cytochrome P-450-reductase
d) Glucuronyl transferase
Answer: Cytochrome P-450
Explanation:
An extremely important function of the microsomal cytochrome P-450 monooxygenase system found associated with the membranes of the smooth ER particularly in liver is the detoxification of xenobiotics.
Cytochrome P-450 monooxygenase system can be used to hydroxylate these toxins, again using NADPH as the source of reducing equivalents.
Q-103. The substance present in the gall bladder stones or the kidney stones can be best identified by the following techniques
a) Fluorescence spectroscopy
b) Electron microscopy
c) Nuclear magnetic resonance
d) X-ray diffraction
Answer: X-ray diffraction
Explanation:
Techniques for analyzing renal and gall bladder stone:
X-ray diffraction
Polarizing microscopy
Infra-red spectroscopy
Q-104. Porphobilinogen in urine produces pink color with
a) Fouchet’s reagent
b) Benedict’s reagent
c) Sodium nitropruside
d) Ehrlich’s aldehyde reagent
Answer: Ehrlich’s aldehyde reagent
Explanation:
Benedict’s reagent: Glucose
Sodium nitropruside: Ketone
Fouchet’s reagent: Bile pigment
Ehrlich’s aldehyde reagent: Porphobilinogen and urobilinogen
Q-105. The buffering capacity of a buffer, is maximum at pH equal to
a) 0.5 pKa
b) pKa
c) pKa + 1
d) 2 pKa
Answer: pKa
Explanation:
The solution resists changes in pH most effectively at pH values close to the pKa. A solution of a weak acid and its conjugate base, buffers most effectively in the pH range pKa 1.0 pH unit.
Q-106. Both Vitamin K and C are involved in:
a) The synthesis of clotting factors
b) Post translational modifications
c) Antioxidant mechanisms
d) The microsomal hydroxylation reactions
Answer: Post translational modifications
Explanation:
Gamma-glutamyl carboxylase is an enzyme that catalyzes the posttranslational modification of vitamin K-dependent proteins. Many of these vitamin K-dependent proteins are involved in coagulation so the function of the encoded enzyme is essential for hemostasis.
The posttranslational modifications of proteins that depend upon vitamin C as a cofactor include proline and lysine hydroxylations and carboxy terminal amidation. The hydroxylating enzymes are identified as prolyl hydroxylase and lysyl hydroxylase. The donor of the amide for C-terminal amidation is glycine. The most important hydroxylated proteins are the collagens. Several peptide hormones such as oxytocin and vasopressin have C-terminal amidation.
Q-107. The amino acid residue having an imino side chain as
a) Lysine
b) Histidine
c) Tyrosine
d) Proline
Answer: Proline
Explanation:
Proline is a unique amino acid having imino group instead of amino group found in other group.
Q-108. Enzyme that moves a molecular group from one molecule to another are known as
a) Ligase
b) Oxido-reductase
c) Transferase
d) Di-peptidase
Answer: Transferase
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-109. Fluoride used in the collection of blood samples for glucose estimation inhibits the enzyme
a) Glucokinase
b) Hexokinase
c) Enolase
d) Glucole-6-phosphatase
Answer: Enolase
Explanation:
Fluoride used in the collection of blood samples for glucose estimation inhibits the enzyme enolase.
Q-110. The predominant isozyme of LDH in cardiac muscle is
a) LD-1
b) LD-2
c) LD-3
d) LD-4
Answer: LD-1
Explanation:
Iso-enzyme LDH-1 expresses the ‘H’ subunit almost exclusively and predominates in the heart.
Iso-enzyme LDH-5 expresses the ‘M’ subunit almost exclusively and predominates in liver.
Important point:
Lactate dehydrogenase is a tetrameric enzyme and consists of four subunits.