Q120. Taq polymerase was originally isolated from which organism?
[RRB Group D — Practice]
- (a) Bacillus anthracis
- (b) Escherichia coli
- (c) Saccharomyces cerevisiae
- (d) Thermus aquaticus
Answer: (d) Thermus aquaticus
Explanation: Taq DNA polymerase comes from the heat-tolerant bacterium Thermus aquaticus. Its thermostability helps it survive the high-temperature DNA-denaturation stages of PCR. This property made automated thermal cycling far more practical than when fresh polymerase had to be added repeatedly.
Q119. During the denaturation step of standard PCR, double-stranded DNA is:
[CGPSC — Practice]
- (a) Broken into free amino acids
- (b) Converted into proteins
- (c) Separated into single strands by heating
- (d) Linked to membrane receptors
Answer: (c) Separated into single strands by heating
Explanation: Heating disrupts hydrogen bonds between complementary bases and separates DNA strands. The next cooling step allows short primers to attach, and polymerase then extends those primers. Repetition of these stages amplifies the target sequence.
Q118. What determines the approximate starting and ending positions of a PCR amplicon?
[UPSC CDS — Practice]
- (a) The concentration of haemoglobin
- (b) Sequence-specific primers
- (c) Only the size of the test tube
- (d) The colour of DNA
Answer: (b) Sequence-specific primers
Explanation: A forward and reverse primer bind opposite strands on either side of the desired region. Their positions define the amplified segment. Primer sequence and annealing conditions affect specificity, while reaction chemistry affects yield and reliability.
Q117. DNA barcoding can help:
1. determine the exact age of an animal;
2. separate visually similar species;
3. identify undeclared species in processed foods.
Which are valid uses?
[UPSC CSE (Pre) 2022]
- (a) 2 and 3
- (b) 3 only
- (c) 1 only
- (d) 1 and 2
Answer: (a) 2 and 3
Explanation: DNA barcoding reads standard genetic markers to identify the species from which a sample originated. It can detect look-alike species and food adulteration. Standard DNA barcodes do not reveal the age of a particular plant or animal.
Q116. Which laboratory method separates DNA fragments mainly by their migration through a gel in an electric field?
[UPSC NDA — Practice]
- (a) Titration
- (b) Distillation
- (c) Centrifugal chromatography only
- (d) Gel electrophoresis
Answer: (d) Gel electrophoresis
Explanation: DNA carries a negatively charged phosphate backbone and migrates toward the positive electrode during electrophoresis. In an appropriate gel matrix, smaller fragments generally travel farther than larger ones. The method supports DNA sizing and checking PCR products.
Q115. In typical agarose electrophoresis, DNA migrates towards the:
[State PSC — Practice]
- (a) Centre of the gel regardless of charge
- (b) Cathode or negative terminal
- (c) Anode or positive terminal
- (d) Nearest light source
Answer: (c) Anode or positive terminal
Explanation: The phosphate groups of DNA confer an overall negative charge. Under an electric field DNA moves toward the positively charged electrode, the anode. Migration distance varies with fragment size, gel concentration and running conditions.
Q114. Which technique reads the order of nucleotides in a DNA sample?
[UPSC CSE — Practice]
- (a) Dialysis
- (b) DNA sequencing
- (c) Protein precipitation
- (d) Osmosis
Answer: (b) DNA sequencing
Explanation: DNA sequencing determines the order of bases in a DNA molecule. Sanger sequencing and high-throughput sequencing use different detection strategies. Sequence data help identify variants, analyse pathogens and map genes across whole genomes.
Q113. In vaccine-platform terminology, which pair is accurate: 1. Covishield uses an mRNA vaccine platform; 2. Sputnik V uses a viral vector; 3. Covaxin contains inactivated virus?
[UPSC CSE (Pre) 2022]
- (a) 2 and 3 only
- (b) 1 and 3 only
- (c) All three
- (d) 1 and 2 only
Answer: (a) 2 and 3 only
Explanation: Covishield and Sputnik V both employ adenoviral vector approaches, whereas Covaxin uses inactivated SARS-CoV-2. Messenger-RNA vaccines constitute another platform. Thus the claim assigning an mRNA platform to Covishield is incorrect; the other two descriptions are accurate.
Q112. A genomic library normally contains:
[WBCS — Practice]
- (a) Only messenger RNA molecules
- (b) Every mineral in a cell
- (c) Only circulating blood proteins
- (d) DNA fragments representing an organism’s genome
Answer: (d) DNA fragments representing an organism’s genome
Explanation: A genomic library is a collection of cloned genomic DNA fragments. With adequate coverage, the inserts collectively represent the genome, including coding and noncoding regions. Libraries may be stored in plasmid, phage or artificial-chromosome vectors.
Q111. A complementary DNA (cDNA) library differs from a genomic library because it is derived from:
[MPPSC — Practice]
- (a) All intergenic DNA exclusively
- (b) Mineral salts
- (c) Mature RNA transcripts
- (d) Cellular membranes
Answer: (c) Mature RNA transcripts
Explanation: A cDNA library is produced by reverse-transcribing RNA, commonly mature messenger RNA, into DNA and cloning it. It chiefly reflects genes expressed in the sampled tissue or condition rather than the entire genomic sequence with introns and intergenic regions.
