Recombinant DNA Basics Practice Questions
20 free Recombinant DNA Basics practice questions for the NCERT Biology. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
Which of the following enzymes is often referred to as 'molecular glue' in recombinant DNA technology?
- A DNA Polymerase
- B Restriction Endonuclease
- C DNA Ligase enzyme
- D Reverse Transcriptase
Correct answer: DNA Ligase enzyme
DNA ligase facilitates the joining of DNA strands together by catalyzing the formation of a phosphodiester bond. It is essential for sealing nicks between the vector and the insert DNA.
Type II restriction endonucleases are preferred in gene cloning because:
- A They cleave DNA at random sites away from the recognition sequence
- B They require ATP for their cleavage activity
- C They cleave DNA at specific palindromic recognition sequences
- D They only work on single-stranded RNA molecules
Correct answer: They cleave DNA at specific palindromic recognition sequences
Type II enzymes are highly predictable as they cut at or within their specific recognition sites. This specificity is crucial for creating precise DNA fragments for cloning.
In the pBR322 vector, the 'rop' gene codes for proteins involved in:
- A Antibiotic resistance against ampicillin
- B The replication of the plasmid
- C The selection of transformants
- D The synthesis of restriction enzymes
Correct answer: The replication of the plasmid
The 'rop' (repressor of primer) gene in pBR322 regulates the copy number of the plasmid by coding for proteins involved in its replication. It ensures the plasmid maintains a consistent presence within the host cell.
The process of introducing recombinant DNA into a bacterial cell by treating it with divalent cations like Calcium is known as:
- A Viral transduction
- B Bacterial conjugation
- C Bacterial transformation
- D Direct transfection method
Correct answer: Bacterial transformation
Transformation involves making bacterial cells 'competent' to take up foreign DNA from their surroundings. Calcium chloride treatment followed by heat shock is a standard method to increase membrane permeability.
What is the function of an 'Ethidium Bromide' (EtBr) dye in agarose gel electrophoresis?
- A To provide weight to the DNA samples so they sink into the wells
- B To act as a pH buffer during the run
- C To intercalate between DNA bases and fluoresce under UV light
- D To denature the double-stranded DNA into single strands
Correct answer: To intercalate between DNA bases and fluoresce under UV light
EtBr is a fluorescent tag that binds to DNA by intercalating between the base pairs. When exposed to ultraviolet light, it allows researchers to visualize the position of DNA bands in the gel.
Which of the following is a characteristic feature of a 'Palindromic sequence' in DNA?
- A It reads the same on both strands when read 5' to 3'
- B The sequence contains only Adenine and Thymine bases
- C The sequence is always 100 base pairs long
- D The sequence is found only in eukaryotic mitochondrial DNA
Correct answer: It reads the same on both strands when read 5' to 3'
A DNA palindrome is a sequence where the top strand read 5' to 3' is identical to the bottom strand read 5' to 3'. Restriction enzymes typically recognize these symmetrical sequences.
In 'Blue-White screening', the appearance of white colonies indicates:
- A The bacteria did not take up any plasmid
- B The bacteria took up the original plasmid without the insert
- C Successful expression of the beta-galactosidase enzyme
- D Insertional inactivation of the lacZ gene
Correct answer: Insertional inactivation of the lacZ gene
If a foreign gene is inserted into the lacZ gene, the enzyme beta-galactosidase is not produced. Without the enzyme, the chromogenic substrate X-gal is not cleaved, resulting in white rather than blue colonies.
Which technique is used to amplify a specific segment of DNA millions of times in a short period?
- A Southern Blotting
- B Polymerase Chain Reaction (PCR)
- C Western Blotting
- D SDS-PAGE gel electrophoresis technique
Correct answer: Polymerase Chain Reaction (PCR)
PCR uses cycles of denaturation, annealing, and extension to exponentially amplify DNA. It relies on a thermostable DNA polymerase to synthesize new strands.
The Ti-plasmid (Tumor-inducing) used as a cloning vector for plants is naturally found in:
- A Escherichia coli
- B Agrobacterium tumefaciens
- C Bacillus thuringiensis
- D Saccharomyces cerevisiae
Correct answer: Agrobacterium tumefaciens
Agrobacterium is a soil bacterium known as 'nature's genetic engineer' because it can transfer a part of its plasmid (T-DNA) into plant cells. Modified Ti-plasmids are used to deliver desired genes into crops.
A genomic library is a collection of:
- A All the proteins expressed in a specific tissue
- B The entire DNA of an organism cloned into vectors
- C Only the mRNA sequences present in a cell
- D Computer-generated DNA sequences for biological research
Correct answer: The entire DNA of an organism cloned into vectors
A genomic library represents the complete genome of an organism. It is created by fragmenting the total DNA and cloning each fragment into a population of vectors.
The 'Taq Polymerase' used in PCR is isolated from which thermophilic bacterium?
- A Thermus aquaticus
- B Aquifex aeolicus
- C Sulfolobus acidocaldarius
- D Pyrococcus furiosus
Correct answer: Thermus aquaticus
Taq polymerase is derived from Thermus aquaticus, an organism that lives in hot springs. Its heat stability allows it to remain functional during the high-temperature denaturation step of PCR.
What is the specific role of 'Selectable Markers' in a cloning vector?
- A To mark the site where DNA is to be cleaved
- B To increase the speed of DNA replication
- C To ensure the protein product is secreted out of the cell
- D To help in identifying and eliminating non-transformants
Correct answer: To help in identifying and eliminating non-transformants
Selectable markers, like antibiotic resistance genes, allow only those cells that have taken up the plasmid to grow on a specific medium. This makes it easy to distinguish successful transformants from unsuccessful ones.
In recombinant DNA technology, 'Sticky ends' are produced by:
- A Restriction enzymes that make staggered cuts in the DNA
- B DNA Ligase during the joining process
- C DNA Polymerase during the extension phase
- D Restriction enzymes that make straight cuts through both strands
Correct answer: Restriction enzymes that make staggered cuts in the DNA
Staggered cuts leave short, single-stranded overhanging sequences called sticky ends. These ends can easily form hydrogen bonds with complementary sequences, increasing the efficiency of ligation.
Which of the following vectors can accommodate the largest size of foreign DNA insert?
- A Plasmid vector
- B Bacteriophage lambda cloning vector
- C Cosmid vector
- D Yeast Artificial Chromosome (YAC)
Correct answer: Yeast Artificial Chromosome (YAC)
YACs are designed to mimic yeast chromosomes and can carry inserts over 1000 kilobases in length. This makes them ideal for large-scale mapping projects like the Human Genome Project.
The 'Biolistics' or gene gun method is primarily used for the transformation of:
- A Cultured animal cells
- B Bacterial cells
- C Fungal spore cells
- D Higher plant cells
Correct answer: Higher plant cells
Biolistics involves firing gold or tungsten microparticles coated with DNA into target cells at high velocity. It is a physical method particularly effective for plant cells that have a thick cell wall.
What is the purpose of 'Reverse Transcriptase' in the production of a cDNA library?
- A To synthesize a DNA strand from an mRNA template
- B To degrade the RNA template after use
- C To join the cDNA to a plasmid vector
- D To identify the sequence of the promoter region
Correct answer: To synthesize a DNA strand from an mRNA template
Reverse transcriptase creates a complementary DNA (cDNA) copy of an mRNA molecule. This allows researchers to clone and study only the expressed (exon) regions of a gene.
A 'Shuttle Vector' is unique because it:
- A Is able to replicate in two different host species
- B Moves rapidly between the nucleus and cytoplasm
- C Can only replicate in the presence of a helper virus
- D Changes its DNA sequence to avoid host immunity
Correct answer: Is able to replicate in two different host species
Shuttle vectors contain origins of replication and selectable markers for two different organisms, such as E. coli and yeast. This allows researchers to manipulate DNA in one host and study its expression in another.
During agarose gel electrophoresis, DNA molecules migrate towards the anode because:
- A DNA is negatively charged due to its phosphate backbone
- B DNA is positively charged due to its nitrogenous bases
- C The anode is at the top of the gel
- D Ethidium bromide adds a negative charge to the DNA
Correct answer: DNA is negatively charged due to its phosphate backbone
The phosphate groups in the DNA backbone give the molecule a net negative charge. Therefore, when an electric field is applied, DNA moves toward the positive electrode (anode).
Which of the following is NOT a requirement for a standard cloning vector?
- A Origin of replication (ori)
- B A selectable marker gene
- C Multiple cloning site (MCS)
- D High intron concentration
Correct answer: High intron concentration
Cloning vectors are designed to be compact and efficient; they do not require introns, which are non-coding regions. The ori, selectable marker, and MCS are the functional essentials for DNA manipulation.
The first restriction endonuclease to be discovered and isolated was:
- A EcoRI
- B BamHI
- C HindIII
- D HindII
Correct answer: HindII
HindII was the first restriction enzyme characterized that cut DNA at a specific sequence. While EcoRI is more famous, HindII set the foundation for the field of recombinant DNA technology.