Q-171. Base substitution mutations can have be following molecular consequence except
a) Changes one codon for an amino acid into another codon for that same amino acid
b) Codon for one amino acid is changed into a codon of another amino acid
c) Reading frame changes downstream to the mutant site
d) Codon for one amino acid is changed into a translation termination codon
Answer: Reading frame changes downstream to the mutant site
Explanation:
A frame shift mutation is a genetic mutation caused by a deletion or insertion in a DNA sequence and resulting m-RNA shows a major alteration downstream to the mutant site.
Q-172. The following methods can be used to detect the point mutation in the beta-globin gene that causes sickle cell anemia except?
a) Polymerase chain reaction with allele-specific oligo-nucleotide hybridization
b) Southern blot analysis
c) DNA sequencing
d) Northern blot analysis
Answer: Northern blot analysis
Explanation:
To detect the point mutation in the beta-globin gene that causes sickle cell anemia require DNA analysis.
Northern blot analysis is used to study the RNA.
Q-173. Vitamin B12 acts as co-enzyme to which one of the following enzymes?
a) Iso-citrate dehydrogenase
b) Homocysteine methyl transferase
c) Glycogen synthase
d) G-6-P dehydrogenase
Answer: Homocysteine methyl transferase
Explanation:
Methyl-malonyl Co-A mutase, leucine amino-mutase, methionine synthase and homocysteine methyl transferase are Vitamin B12 dependent enzyme. .
- All of the following enzymes are regulated by calcium or calmodulin except
a) Adenylate cyclase
b) Glycogen synthase
c) Guanylyl cyclase
d) Hexokinase
Answer: Hexokinase
Explanation:
Enzymes regulated by calcium or calmodulin:
Adenylate cyclase
Guanylyl cyclase
Glycogen synthase
Pyruvate carboxylase
Pyruvate dehydrogenase
Pyruvate kinase
- A common feature of all serine proteases
a) Autocatalytic activation of zymogen precursor
b) Tight binding of pancreatic trypsin inhibitor
c) Cleavage of protein on the carboxyl site of serine residues
d) Presence of Ser-His-Asp catalytic triad at the active site
Answer: Presence of Ser-His-Asp catalytic triad at the active site
Explanation:
While catalysis by aspartic proteases involves the direct hydrolytic attack of water on a peptide bond, catalysis by the serine protease chymo-trypsin involves prior formation of a covalent acyl enzyme intermediate, a highly reactive seryl residue, serine 195, participates in a charge-relay network with histidine 57 and aspartate 102.
Trypsin and elastase employ a similar catalytic mechanism, but the numbers of the residues in their Ser -His-Asp proton shuttles differ.
Serine proteases- Are characterized by having several active sites per molecule, each containing a serine residue.
Important points:
The active sites of serine proteases contain three critical amino acids Ser -His-Asp.
These residues are often referred to as the catalytic triad.
Q-176. Dinitrophenol causes:
a) Inhibition of ATP synthase
b) Inhibition of electron transport
c) Uncoupling of oxidation and phosphorylation
d) Accumulation of ATP
Answer: Uncoupling of oxidation and phosphorylation
Explanation:
2, 4-Dinitrophenol is an inhibitor of efficient energy (ATP) production in cells with mitochondria.
It uncouples oxidative phosphorylation by carrying protons across the mitochondrial membrane, leading to a rapid consumption of energy without generation of ATP.
Q-177. All of the following are true regarding oxygenases except
a) Incorporate 2 atoms of oxygen
b) Incorporate 1 atom of oxygen
c) Required for hydroxylation of steroids
d) Required for carboxylation of drugs
Answer: Required for carboxylation of drugs
Explanation:
Carboxylation is a function of carboxylase enzyme belonging to class of ligases.
Mono-oxygenase incorporates one atom of oxygen and plays an important role in hydroxylation of steroids.
Dio-oxygenase incorporates 2 atoms of oxygenase into the substrate.
Q-178. Treatment of multiple carboxylase deficiency is
a) Biotin
b) Pyridoxine
c) Thiamine
d) Folic acid
Answer: Biotin
Explanation:
Multiple carboxylase deficiency is characterized by deficient activities of three biotin-dependent enzymes, propionyl coenzyme A carboxylase, pyruvate carboxylase, and beta-methylcrotonyl coenzyme A carboxylase.
Main symptoms and signs are feeding difficulties, neurologic abnormalities (hypotonia, impaired consciousness, seizures and ataxia) and cutaneous changes (rash, alopecia).
Treatment of multiple carboxylase deficiency is administration of biotin.
Q-179. Basement membrane degeneration is mediated by
a) Metalloproteinases
b) Oxidases
c) Elastases
d) Hydroxylases
Answer: Metalloproteinases
Explanation:
Degradation of collagen and other ECM proteins is achieved by a family of matrix metallo-proteinases which are dependent on Zinc ions for their activity.
Q-180. Which of the following enzymes is stable at acidic pH?
a) Pepsin
b) Trypsin
c) Chymotrypsin
d) Carboxy-peptidase
Answer: Pepsin
Explanation:
Pepsin is stable at such acidic pH in stomach and its action is terminated in alkaline pH.
Enzymes stable at acidic pH:
Trypsin
Chymotrypsin
Carboxy-peptidase