Q.(a) 'Insertional inactivation' is a method to detect recombinant DNA. Explain the method.
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🔒 Start your 14-day free trial to unlock the full solution →Part (a)Concept understanding — Cloning Vectors and Selectable Markers (pBR322)
Cloning Vectors and Selectable Markers (pBR322)
A cloning vector is a DNA molecule that can carry a foreign DNA fragment into a host cell and replicate there. Plasmids such as pBR322, an early and widely used E. coli cloning vector, are drawn as circular DNA maps and have several essential features that a good vector must possess.
- Origin of replication (ori): the sequence at which replication starts; it controls copy number (how many copies of the plasmid are made per cell). In pBR322 the rop gene near the ori helps regulate this copy number.
- Selectable markers: genes that allow cells carrying the vector to be distinguished from those that do not, usually by giving antibiotic resistance. pBR322 carries two such genes — ampicillin resistance (ampR) and tetracycline resistance (tetR). …
Part (b)Concept understanding — Recombinant DNA Technology
Imagine you have a cookbook with recipes from all over the world. Normally, you can only cook what's in one book at a time. But what if you could cut out the best recipe from one book and paste it into another, so your new book has a dish that no single cuisine ever had before? That is the basic idea behind Recombinant DNA Technology.
At its simplest, this technology is a way to take a piece of DNA (the genetic instruction manual) from one organism and join it with the DNA of a completely different organism. The result is a new, "recombinant" DNA molecule — a hybrid that never existed in nature. Think of it as genetic tailoring: you cut a gene from a human, a bacterium, or a plant, and stitch it into the DNA of another organism, often a bacterium or yeast. That host organism then reads the new instructions and starts producing the protein the inserted gene codes for.
Why does this matter? Because it lets us manufacture things that living organisms naturally make, but in a controlled, large-scale way. For example, the human insulin gene can be inserted into E. coli bacteria. These bacteria then become tiny factories, churning out human insulin that can be purified and given to diabetic patients. Before this technology, insulin had to be extracted from the pancreases of cows and pigs — a slow, expensive, and sometimes allergenic process.
The NCERT textbook (Class 12 Biology, Chapter 11) defines it precisely: Recombinant DNA Technology is the technique of joining DNA from two different species and inserting it into a host organism to produce a new genetic combination. The textbook highlights three key tools that make this possible:
- Restriction Enzymes – These are the "molecular scissors" that cut DNA at specific, predictable points. They allow scientists to cut out a desired gene cleanly.
- Vectors – These are the "delivery vehicles," usually plasmids (small circular DNA in bacteria) or viruses, that carry the foreign DNA into the host cell.
- Host Organisms – The living factory (like bacteria, yeast, or plant cells) that will replicate the recombinant DNA and produce the desired protein.
The core principle is genetic recombination — creating a DNA molecule that contains sequences from two or more different sources. This is not the same as natural reproduction or mutation; it is a deliberate, laboratory-made hybrid.
The process itself follows a clear sequence:
- Isolation of the desired gene (say, the human insulin gene) from the donor organism's DNA.
- Cutting both the gene and the vector DNA with the same restriction enzyme, creating matching "sticky ends."
- Ligation — using an enzyme called DNA ligase to permanently join the gene and the vector, forming the recombinant DNA.
- Transformation — inserting this recombinant DNA into a host cell (like a bacterium).
- Selection — identifying and growing only those host cells that successfully took up the recombinant DNA.
- Expression — getting the host cells to produce the desired protein in large quantities.
A common confusion is thinking this technology creates "new life." It does not. It creates a new genetic combination inside an existing living cell. The host organism remains the same species, but it now carries an extra instruction — like a factory that gets a new blueprint for a product it never made before. …
Part (a)
Insertional inactivation identifies recombinant colonies by disrupting a marker gene. In a vector like pBR322, foreign DNA is inserted into a restriction site within an antibiotic-resistance gene (e.g., tetracycline resistance). Insertion inactivates that gene, so recombinants become sensitive to tetracycline while remaining resistant to the second antibiotic (ampicillin). Non-recombinants keep both resistances. Recombinants are thus recognised as Amp-resistant, Tet-sensitive colonies. (A faster version uses insertion into lacZ, giving colourless/white colonies instead of blue.) …
Part (a): Insertional inactivation clones foreign DNA into a marker gene so the insertion destroys that gene's function, letting recombinants be selected as Amp-resistant/Tet-sensitive (or white lacZ colonies).
Part (b): PCR amplifies the suspect sequence and a labelled complementary DNA probe hybridises to it, revealing a mutation or low-level pathogen before symptoms appear.
Part (a)
Concept-first idea: After ligation we need to tell recombinant plasmids (carrying insert) from non-recombinant ones. Insertional inactivation does this by making a successful insertion destroy a detectable marker.
Method.
- Use a vector such as pBR322 carrying two antibiotic-resistance genes — e.g., ampicillin resistance (amp^R) and tetracycline resistance (tet^R).
- Insert foreign DNA at a restriction site located within one marker (say inside tet^R).
- The insertion interrupts and inactivates tet^R, so the recombinant cell can no longer make functional tetracycline-resistance protein, but amp^R stays intact.
- Select transformants on ampicillin (only cells with a plasmid survive), then replica-plate onto tetracycline:
- Non-recombinants (empty vector) grow on both antibiotics.
- Recombinants grow on ampicillin but not tetracycline.
- Colonies that are Amp-resistant, Tet-sensitive carry the recombinant DNA. …
Showing the 12 most recent of 20 on this concept.
- AP EAPCET 2026Set ap-2026-05-19-FN1 markMCQQ.DNA polymerase and deoxynucleotides helps this step in polymerase chain reaction (A) Denaturation (B) Annealing (C) Extension (D) Amplificating
›Reveal solutionSolution
DNA polymerase + dNTPs act specifically during PCR's extension step, synthesising new DNA from the annealed primers.
Concept and Intuition
PCR cycles through three temperature-defined steps: denaturation (heating to separate the double-stranded template into single strands), annealing (cooling to let short primers bind/hybridise to complementary sequences flanking the target region), and extension (an intermediate temperature at which a thermostable DNA polymerase, typically Taq polymerase from Thermus aquaticus, adds free deoxynucleotides one by one, extending each primer to synthesise a new complementary strand). It is specifically in this extension step that DNA polymerase and dNTPs do their work.
Step-by-Step Solution
- Recall the three PCR steps and what happens in each: denaturation (heat, strand separation), annealing (primer binding), extension (new strand synthesis). …
- AP EAPCET 2026Set ap-2026-05-20-AN1 markMCQQ.During the isolation of desired gene from the fungal cell which enzyme is not used? (A) Chitinase (B) RNase (C) Lysozyme (D) Protease
›Reveal solutionSolution
This tests knowledge of cell-lysis enzymes used in genetic-engineering protocols:
chitinase (fungal wall), cellulase (plant wall), lysozyme (bacterial wall) are each
matched to a specific cell type — lysozyme does not act on fungal cells.
Concept and Intuition
The first step of isolating a gene (or any DNA) from a cell is breaking open the
cell to release its DNA along with other biomolecules. Different organisms have
chemically different cell walls, so the enzyme used to breach the wall must match
the wall's composition:
- Bacterial cell walls are made of peptidoglycan → broken down by lysozyme.
- Fungal cell walls are made largely of chitin → broken down by chitinase.
- Plant cell walls are made of cellulose → broken down by cellulase. Once the cell is lysed, the crude extract (containing DNA, RNA, and protein) is treated with RNase to digest RNA and protease to digest protein, leaving purified DNA.
Step-by-Step Solution
- The question restricts the scenario to a fungal cell specifically.
- Chitinase: breaks down the chitin fungal cell wall — used here. ✓
- RNase: removes RNA contamination from the lysate regardless of source organism — used here. ✓
- Protease: removes protein contamination from the lysate regardless of source organism — used here. ✓ …
- AP EAPCET 2025Set ap-2025-05-19-FN1 markMCQQ.Methods which help in the insertion of recombinant DNA into the host I. Selectable marker II. Disarmed pathogen vector III. Boilistic method IV. Micro injection (A) I, II, III (B) II, III, IV (C) I, III, IV (D) I, II, IV
›Reveal solutionSolution
Selectable markers help identify transformed cells but do not insert DNA; disarmed pathogen vectors, biolistics, and microinjection are the actual DNA-delivery methods — II, III, IV. Answer: (B).
Concept and Intuition
Introducing foreign/recombinant DNA into a host cell requires an actual delivery mechanism. Several established methods exist: (i) using a disarmed pathogen (vector), such as a modified, non-pathogenic strain of Agrobacterium tumefaciens, which naturally transfers a piece of its DNA (T-DNA) into plant cells — this can be re-engineered to carry genes of interest instead;
(ii) the biolistic (particle bombardment / "gene gun") method, in which DNA-coated metal particles are physically shot into cells;
(iii) microinjection, in which DNA is directly injected into a cell (or its nucleus) using a fine glass needle. In contrast, a selectable marker (e.g., an antibiotic-resistance gene included alongside the gene of interest) is used AFTER the transformation attempt, to distinguish and select the (typically rare) cells that successfully took up the foreign DNA from those that did not — it is a screening/selection tool, not a delivery mechanism.
Step-by-Step Solution
- (I) Selectable marker — this helps select successfully transformed cells; it does not insert DNA into the host. EXCLUDE. …
- AP EAPCET 2025Set ap-2025-05-20-AN1 markMCQQ.Bond formed by DNA ligase (A) Hydrogen bond (B) Glycosidic bond (C) Phosphodiester bond (D) Peptide bond
›Reveal solutionSolution
DNA ligase seals nicks in the sugar-phosphate backbone by forming a phosphodiester bond.
Concept and Intuition
DNA ligase catalyses the formation of a phosphodiester bond between the 3'-OH end of one DNA strand and the 5'-phosphate end of the adjacent strand, sealing nicks in the backbone — this is essential both in DNA replication and in recombinant DNA technology for joining a vector and a foreign DNA fragment.
Step-by-Step Solution
- DNA ligase's job is to seal breaks in the DNA backbone.
- This sealing is chemically the formation of a phosphodiester bond linking adjacent nucleotides.
- Answer: (C) Phosphodiester bond. …
- AP EAPCET 2025Set ap-2025-05-20-FN1 markMCQQ.It helps in identifying and eliminating non transformants (A) Restriction enzyme (B) Antibiotic (C) Selectable marker (D) Plasmid
›Reveal solutionSolution
Selectable markers are genes (often for antibiotic resistance) included in a vector so that only successfully transformed cells survive a selective condition, letting non-transformants be identified and eliminated — option (C).
Concept and Intuition
When host cells are exposed to foreign DNA, only a fraction actually take it up and express it (transformants); a selectable marker gene, co-transferred with the gene of interest, provides a survival advantage (or detectable trait) only in successfully transformed cells, letting the rest be weeded out.
Step-by-Step Solution
- Restriction enzymes are used to cut DNA at specific sites — not for identifying transformants.
- An antibiotic by itself is simply the selective agent applied; the actual genetic feature that confers resistance (and thus distinguishes transformants) is the selectable marker gene. …
- AP EAPCET 2024Set ap-2024-05-16-AN1 markMCQQ.Assertion (A): DNA fragments are positively charged. Reason (R): DNA fragments are separated by gel electrophoresis technique. (A) A and R are correct. R is the correct explanation of A (B) A and R are correct. R is not the correct explanation of A (C) A is correct but R is incorrect (D) A is incorrect but R is correct
›Reveal solutionSolution
DNA fragments are negatively (not positively) charged, making the Assertion false, while the Reason - that gel electrophoresis separates DNA fragments - is a true, independent statement.
Concept and Intuition
DNA's backbone is built from alternating deoxyribose sugar units and phosphate groups, and at physiological/typical experimental pH, each phosphate group carries a negative charge (from its ionised oxygen atoms). This makes the entire DNA molecule strongly negatively charged, not positively charged. This negative charge is in fact the very property exploited in agarose gel electrophoresis: when an electric field is applied across the gel, negatively charged DNA fragments migrate toward the positive electrode (anode), with smaller fragments moving faster through the gel matrix than larger ones, allowing size-based separation.
Step-by-Step Solution
- Evaluate Assertion: DNA fragments are positively charged - false; DNA is negatively charged due to its phosphate backbone.
- Evaluate Reason: DNA fragments are separated by gel electrophoresis technique - true, this is a standard, independently valid fact. …
- AP EAPCET 2024Set ap-2024-05-17-AN1 markMCQQ.While isolating DNA from bacteria the following enzyme is not used. (A) Lysozyme (B) Ribonuclease (C) Deoxyribonuclease (D) Protease
›Reveal solutionSolution
This tests the standard DNA-isolation protocol. Every enzyme used in the protocol removes something OTHER than DNA (wall, RNA, protein) — an enzyme that degrades DNA itself can never be part of the process.
Concept and Intuition
To isolate DNA in pure form we must strip away everything else in the cell — the wall/membrane, the RNA, and the proteins bound to DNA (histones etc.) — while leaving the DNA itself completely intact. So every enzyme deliberately chosen for the protocol must act on a non-DNA target.
Step-by-Step Solution
- Cell lysis: bacterial cells are treated with lysozyme, which hydrolyses the peptidoglycan cell wall, releasing the cell contents.
- Removing RNA: ribonuclease (RNase) is added to degrade contaminating RNA, since RNA would otherwise co-precipitate with DNA.
- Removing protein: protease digests proteins (including histones and enzymes) bound to the DNA, freeing the nucleic acid. …
- AP EAPCET 2024Set ap-2024-05-17-FN1 markMCQQ.Assertion [A] : In general Gene gun method is used to insert DNA into the competent host Reason [R] : In biolistic method, cells are bombarded with DNA coated with micro particles of gold. (A) A and R are correct. R is the correct explanation of A (B) A and R are correct. R is not the correct explanation of A (C) A is correct but R is incorrect (D) A is incorrect but R is correct
›Reveal solutionSolution
Tests whether the gene gun (biolistic) method is correctly linked to the concept of a 'competent host'. It is not — that term belongs to chemical bacterial transformation. Answer: (D).
Concept and Intuition
There are several distinct ways to introduce foreign DNA into a cell:
- Chemical-mediated transformation of bacteria: cells are first made 'competent' to take up DNA (e.g., treated with a divalent cation like CaCl₂ and given a heat shock).
- Micro-injection: DNA is injected directly into the nucleus of an animal cell.
- Biolistics / Gene gun: cells (typically plant cells) are physically bombarded with high-velocity micro-particles of gold or tungsten coated with DNA — the particle's velocity, not any chemical 'competence', is what gets the DNA inside.
- Disarmed pathogen vectors (e.g., Agrobacterium) that naturally infect and transfer DNA. The assertion conflates the gene-gun method with the specific 'competent host' terminology that belongs to the chemical transformation route.
Step-by-Step Solution
- Read Reason R: it accurately restates the biolistic method — cells bombarded with DNA-coated gold micro-particles. This is textbook-correct. R is TRUE.
- Read Assertion A: it claims gene gun is used to insert DNA 'into the competent host'. But 'competent' cells are specifically bacterial cells chemically prepared for DNA uptake — an entirely different technique from the physical force used in biolistics. …
- AP EAPCET 2023Set ap-2023-05-22-FN1 markMCQQ.Choose the wrong pair corresponding to selection of transformed cells (A) BamH I site – tetracycline resistance (B) β galactosidase – inactivation of the enzyme (C) Ampicillin resistance – selectable marker (D) Insertional inactivation – Development of blue color
›Reveal solutionSolution
Insertional inactivation of beta-galactosidase produces WHITE (not blue) colonies — recombinants lose colour, they do not gain it — making (D) the wrong pair.
Concept and Intuition
Cloning vectors like pBR322 carry unique restriction sites inside their antibiotic-resistance genes (e.g., BamHI within the tetracycline-resistance gene, PstI within the ampicillin-resistance gene), so inserting foreign DNA there destroys that resistance — a way to screen for successful inserts by loss of a phenotype (insertional inactivation). A cleaner version of the same idea uses the lacZ (beta-galactosidase) gene: an intact lacZ gene hydrolyses the substrate X-gal to produce a blue product, so vector-only (non-recombinant) colonies turn BLUE. When foreign DNA is inserted inside lacZ, it disrupts (inactivates) the gene, beta-galactosidase is not made, X-gal is not cleaved, and recombinant colonies stay WHITE.
Step-by-Step Solution
- (A) BamHI site lies within the tetracycline-resistance gene of pBR322 — a standard, correctly stated fact.
- (B) Beta-galactosidase's role in screening is exactly "inactivation of the enzyme" upon insertion — correctly stated.
- (C) Ampicillin resistance is a textbook example of a selectable marker gene — correctly stated. …
- AP EAPCET 2023Set ap-2023-05-23-AN1 markMCQQ.Name and arrange the following in the order of technique and steps for separation and isolation of DNA fragments I. DNA fragments moved towards anode under electric field. II. Exposure to UV radiation. III. DNA fragments stained with EBr. IV. Gel electrophoresis. V. Elution. (A) V II III I IV (B) IV V I III II (C) III II I V IV (D) IV I III II V
›Reveal solutionSolution
This tests the correct sequence of steps in agarose gel electrophoresis used to separate and isolate DNA fragments. The order is: set up gel electrophoresis, fragments migrate to the anode, stain with EtBr, view under UV, then elute — i.e. IV, I, III, II, V.
Concept and Intuition
DNA is negatively charged (due to its phosphate backbone), so when placed in an agarose gel and subjected to an electric field, it moves towards the positive electrode (anode). Smaller fragments move faster/further than larger ones, separating them by size. Because DNA itself is not visible to the naked eye, the gel is stained with a fluorescent dye, ethidium bromide (EtBr), which intercalates into the DNA. Only after staining can the bands be visualised — and this is done by exposing the gel to UV light, under which the DNA-EtBr complex fluoresces orange. Once a band of interest is located, that portion of the gel is cut out and the DNA is recovered from the gel piece by elution.
Step-by-Step Solution
- Gel electrophoresis (IV) — the DNA sample (a mixture of fragments) is loaded into wells of an agarose gel and an electric field is applied.
- DNA fragments move towards the anode (I) — being negatively charged, the fragments migrate through the gel matrix towards the positive electrode, separating by size.
- DNA fragments stained with EtBr (III) — the gel is soaked in/pre-mixed with ethidium bromide so that DNA becomes visualisable. …
- AP EAPCET 2022Set ap-2022-07-11-AN1 markMCQQ.A technique to alter the chemistry of the Genetic material DNA and RNA is (A) Bio chemistry (B) Genetic engineering (C) Bio science (D) Microbiology
›Reveal solutionSolution
Genetic engineering is defined as the deliberate alteration of the chemical/molecular structure of DNA and RNA to achieve a desired genetic outcome.
Concept and Intuition
Genetic engineering (recombinant DNA technology) refers to the set of techniques by which genetic material (DNA or RNA) is directly manipulated — cut, modified, recombined, and introduced into a host organism. This differs from general biochemistry (which studies the chemistry of all biomolecules), bioscience (a broad umbrella term), and microbiology (the study of microorganisms), none of which specifically denote altering genetic material's chemistry.
Step-by-Step Solution
- Parse the question: it seeks the specific technique for altering the chemistry of DNA/RNA (the genetic material).
- Genetic engineering is precisely this: using enzymes (restriction endonucleases, ligases, polymerases) to cut, modify, and recombine DNA/RNA sequences. …
- AP EAPCET 2022Set ap-2022-07-12-FN1 markMCQQ.The enzyme helpful in joining the DNA fragments. (A) Exo-nuclease (B) Nuclease (C) DNA ligase (D) Polymerase
›Reveal solutionSolution
DNA ligase seals the sugar-phosphate backbone nicks between adjacent DNA fragments, joining them into a continuous strand — essential in both DNA replication (joining Okazaki fragments) and recombinant DNA technology.
Concept and Intuition
DNA ligase catalyses the formation of a phosphodiester bond between the 3'-OH end of one DNA fragment and the 5'-phosphate end of the adjacent fragment, effectively 'sealing' nicks in the DNA backbone. This is essential both during normal replication (to join Okazaki fragments on the lagging strand) and in genetic engineering (to join a foreign DNA insert to a vector). Exonucleases and nucleases cut/degrade DNA rather than join it, and polymerases synthesize new strands by adding nucleotides but do not seal existing nicks between two separate fragments.
Step-by-Step Solution
- Joining two DNA fragments requires sealing the nick in the sugar-phosphate backbone. …
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