Q-141. Xeroderma pigmentosa is caused due to a group of closely related abnormalities in:
a) Mismatch repair
b) Base excision repair
c) Nucleotide excision repair
d) SOS repair
Answer: Nucleotide excision repair
Explanation:
Xeroderma pigmentosum is a rare disorder transmitted in an autosomal recessive manner.
The basic defect in xeroderma pigmentosum is in nucleotide excision repair (NER), leading to deficient repair of DNA damaged by UV radiation.
The most common form of this disease is caused by the absence of the UV-specific excinuclease.
Q-142. Substitution of which one of the following amino acids in place of alanine would increase the absorbance of protein at 280 nm:
a) Leucine
b) Arginine
c) Tryptophan
d) Proline
Answer: Tryptophan
Explanation:
Amino acids do not absorb visible light and thus are colorless. However, tyrosine, phenylalanine, and especially tryptophan absorb high-wavelength (250-290 nm) ultraviolet light. Because it absorbs ultraviolet light about ten times more efficiently than either phenylalanine or tyrosine, tryptophan makes the major contribution to the ability of most proteins of absorb light in the region of 280 nm.
Q-143. Secretory proteins are synthesized in:
a) Cytoplasm
b) Endoplasmic reticulum
c) First in cytoplasm and then in Endoplasmic Reticulum
d) First in Endoplasmic Reticulum and then in cytoplasm
Answer: Endoplasmic reticulum
Explanation:
Rough Endoplasmic Reticulum -> Golgi body-> Secretory vesicles
Q-144. To synthesize insulin on a large scale basis, the most suitable starting material obtained from the beta cells of the pancreas is:
a) Genomic DNA
b) Total cellular RNA
c) c-DNA of insulin
d) m-RNA of insulin
Answer: m-RNA of insulin
Explanation:
Insulin is synthesized on a large scale basis from complementary DNA (cDNA), but this is not the starting material because these cDNAs are derived from mRNAs with the help of Reverse transcriptase and DNA polymerase 1.
The cDNA produced by this method is inserted into an appropriate cloning vector which produces a large number of cDNA clones.
Q-145. If cellular proteins do not fold into a specific conformation, their functions are affected. Certain disorders arise, if specific proteins are mis-folded. Which of the following disorders arises due to conformational isomerization?
a) Fatal familial insomnia
b) Hepatitis delta
c) Pernicious anemia
d) Lesch-Nyhan syndrome
Answer: Familial fatal insomnia
Explanation:
The term “prions” refers to abnormal, pathogenic agents that are transmissible and are able to induce abnormal folding of specific normal cellular proteins called prion proteins that are found most abundantly in the brain.
Prion diseases are usually rapidly progressive and always fatal.
Human Prion Diseases:
Creutzfeldt – Jakob disease (CJD)
Variant Creutzfeldt – Jakob disease (vCJD)
Gerstmann-Sträussler-Scheinker Syndrome
Fatal Familial Insomnia
Kuru
Animal Prion Diseases:
Bovine Spongiform Encephalopathy (BSE)
Chronic Wasting Disease (CWD)
Scrapie
Transmissible mink encephalopathy
Feline spongiform encephalopathy
Ungulate spongiform encephalopathy
- A nucleic acid was analyzed and found to contain 32% adenine, 18% guanine, 17% cytosine and 33% thymine. The nucleic acid must be:
a) Single-stranded RNA
b) Single-stranded DNA
c) Double—stranded RNA
d) Double stranded DNA
Answer: Double—stranded DNA
Explanation:
Chargaff’s Rule:
In any sample of double stranded DNA
A = T
G = C
A + G = C + T
- The type of enzyme inhibition in which succinate dehydrogenase reaction is inhibited by malonate is an example of:
a) Noncompetitive
b) Uncompetitive
c) Competitive
d) Allosteric
Answer: Competitive
Explanation:
Most frequently in competitive inhibition; the inhibitor binds to the substrate-binding portion of the active site, thereby blocking access by the substrate.
The structures of most classic competitive inhibitors therefore tend to resemble the structures of a substrate, and thus are termed substrate analogs.
Inhibition of the enzyme succinate dehydrogenase by malonate illustrates competitive inhibition by a substrate analog.
Q-148. The electron flow in Cytochrome C oxidase can be blocked by:
a) Rotenone
b) Antimycin-A
c) Cyanide
d) Actinomycin
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-149. Chymotrypsinogen is
a) Zymogen
b) Carboxy-peptidase
c) Elastase
d) Transaminase
Answer: Zymogen
Explanation:
Zymogens are inactive precursors of secreted enzymes including proteases required for digestion.
They become activated through cleavage when they reach their proper sites of action.
Examples of zymogens:
Trypsinogen
Chymotrypsinogen
Pepsinogen
Pro-elastase
Pro-carboxy-peptidase
Most proteins in the coagulation system
Angiotensinogen
Pro-Caspases
Q-150. Steroid regulatory protein mediate the act by binding at
a) Leucine zipper motif
b) Zinc finger motif
c) Helix turn helix motif
d) Histone helix motif
Answer: Zinc finger motif
Explanation:
Several motifs mediate the binding of regulatory proteins to DNA.
Three unique motifs- the helix turn helix, the zinc finger and the Leucine zipper account for many of specific protein-DNA interaction.
Helix turn helix motif– Homeobox proteins, Pit-1, Oct-1, Oct-2
Zinc finger motif– Sp1, Steroid receptor family
Leucine zipper motif– c-myc, n-myc, l-myc, CRE binding protein