NEET Biotechnology: Principles and Processes Previous Year Questions with Solutions

Annealing involves the hybridization of two sets of oligonucleotide primers to the single-stranded template DNA at an optimal temperature (typically 50–60°C).

• • Primers are small chemically synthesized oligonucleotides complementary to the regions of DNA.

Denaturation uses heat (~94°C) to break hydrogen bonds between complementary strands. Extension (~72°C) uses thermostable DNA polymerase (Taq polymerase isolated from Thermus aquaticus) and dNTPs to extend the primers.

• • Repeated cycles achieve billion-fold amplification (~10⁹ times).

Plasmids are naturally occurring, double-stranded, closed-circular, extrachromosomal DNA molecules found in bacteria and some yeasts that replicate autonomously independent of genomic DNA.

• • Statement I is completely correct.

Plasmids have the ability to replicate within bacterial cells independent of chromosomal DNA control. Because they can carry foreign passenger DNA linked to their origin of replication and selectable markers (e.g., antibiotic resistance genes), they are the most widely used cloning vectors in genetic engineering.

• • Statement II is completely correct.

To isolate pure DNA, the cell envelope must be broken open to release DNA along with other macromolecules. Since bacterial, plant, and fungal cells possess rigid cell walls of distinct chemical nature, specific hydrolytic enzymes are required.

• • Assertion (A) is completely true.

Lysozyme specifically hydrolyzes the β(1→4) glycosidic bonds between NAM and NAG in peptidoglycan, but cannot hydrolyze cellulose. Conversely, cellulase specifically cleaves β(1→4) glucan bonds in plant cellulose. Thus, Reason (R) is true and is the exact biochemical explanation for Assertion (A).

• • Subsequent treatment with ribonuclease removes RNA, and protease removes proteins, before ice-cold ethanol precipitates purified DNA.

NCERT defines the four indispensable features required to facilitate cloning into a vector:

• • Selectable markers typically include antibiotic resistance genes such as ampicillin, tetracycline, chloramphenicol, or kanamycin resistance.

Aligning all four pairs gives: A-II, B-I, C-IV, D-III, which uniquely corresponds to Option (1).

• • Completes the entire set of 180 questions for NEET 2026!

PCR involves three successive steps repeated over multiple thermal cycles: denaturation of double-stranded DNA (~94 °C), primer annealing (~54 °C), and primer extension by thermostable Taq DNA polymerase (~72 °C):

• • Because both strands of every double helix serve as templates in subsequent cycles, the population of target DNA molecules doubles in every completed cycle.

For an initial population of N₀ template DNA molecules amplified over n cycles:

• • For a single initial starting molecule (N₀ = 1), the number of amplified copies is given by the power equation 2ⁿ.
• • After 30 cycles, approximately 2³⁰ (over 1 billion) copies are generated.
• • Matches Option (2) 2ⁿ.

Selection of recombinants due to inactivation of antibiotics requires simultaneous replica plating on two different antibiotic plates, which is cumbersome:

• • Alternative selectable markers differentiate recombinants from non-recombinants on the basis of their ability to produce colour in the presence of a chromogenic substrate.
• • Here, a recombinant DNA is inserted within the coding sequence of the enzyme $\beta$-galactosidase (encoded by the *lacZ* gene).

Evaluating the two bacterial populations:

• • Non-recombinant colonies: The plasmid does not have an insert; the $\beta$-galactosidase gene remains intact and produces active enzyme, which hydrolyzes the chromogenic substrate X-gal (5-bromo-4-chloro-3-indolyl-$\beta$-D-galactopyranoside) to produce an insoluble blue dye -> Blue colonies.
• • Recombinant colonies: Insertion of alien DNA at the EcoRI site disrupts the $\beta$-galactosidase reading frame (insertional inactivation). No functional enzyme is made, so no blue pigment is formed -> White colonies.

Because recombinant bacteria fail to produce color due to insertional inactivation, researchers select the white-colored colonies.

Bioreactors provide optimal conditions for achieving desired products (temperature, pH, substrate, salts, vitamins, oxygen). A simple stirred-tank bioreactor has specific essential subsystems:

• • Agitator system: Includes an overhead motor (B) driving a central shaft with flat-bladed impellers (A) to ensure uniform mixing and oxygen availability throughout the vessel.
• • Foam control system: Microbial fermentation with aeration creates violent bubbling and vigorous froth/foam at the liquid-air interface, which can clog exhaust filters and cause contamination. A rotating foam breaker (C) mounted near the liquid surface mechanically disintegrates this foam.
• • Aeration system: Injects sterile air via a sparger (D) at the base of the vessel.
• • Temperature, pH control systems, and sampling ports.

Matching the labels:

• • B -> Motor.
• • C -> Foam breaker.
• • A -> Flat bladed impeller (agitator).
• • D -> Sterile air sparger / line.

Part C is explicitly identified as the foam breaker. This corresponds to Option (4).

Separation of restriction enzyme-digested DNA fragments relies on charge-to-mass uniformity and size-dependent molecular sieving:

• • DNA fragments carry uniform negative charges along their phosphate backbones and migrate towards the positive electrode (anode) when an electric field is applied.
• • The matrix (agarose gel) acts as a molecular sieve: smaller fragments experience less frictional resistance and travel farther towards the anode.
• • Larger fragments encounter high hydrodynamic drag and remain near the loading wells at the cathodic end.
• • Hence, Statement II is completely CORRECT.

Post-electrophoretic utilization of resolved DNA fragments in genetic engineering:

• • DNA bands are visualized by staining with ethidium bromide (EtBr) under ultraviolet (UV) light as bright orange-colored bands.
• • The desired DNA band is excised from the agarose gel and extracted/purified via elution.
• • The purified fragment of interest is subsequently ligated into a linearized cloning vector using DNA ligase to produce recombinant DNA (rDNA).
• • Hence, Statement I is completely CORRECT.

Both Statement I and Statement II are factually and conceptually correct, matching Option (1).

Construction of a recombinant DNA molecule involves a defined set of biochemical catalytic tools:

• • Restriction Endonucleases (A): Molecular scissors that cleave phosphodiester backbones at specific palindromic recognition sites to yield compatible fragments.
• • DNA Ligase (B): Molecular glue that joins the vector DNA and source insert DNA by synthesizing covalent phosphodiester bonds between adjacent 3'-OH and 5'-phosphate termini.
• • DNA Polymerase (E): Enzymes like thermostable *Taq* polymerase essential for *in vitro* exponential amplification of the target gene via Polymerase Chain Reaction (PCR).

Analyzing candidates C and D in the context of gene cloning:

• • C. DNA mutase: A non-existent or irrelevant enzyme class in recombinant DNA technology. Gene cloning aims to preserve high-fidelity replication of unmutated genes, making mutases completely antithetical and non-essential.
• • D. DNA recombinase: Endogenous cellular enzymes (e.g. Cre, FLP, RecA) that catalyze somatic or homologous crossing over in living cells. They are not part of the standard core tools required for *in vitro* cutting, ligating, and cloning target genes into plasmids.

DNA mutase (C) and DNA recombinase (D) are NOT essential for gene cloning, matching Option (1).

Blue-white screening is an elegant single-step chromogenic method to identify bacterial transformants carrying recombinant plasmids:

• • Cloning vectors (e.g. pUC19) contain a multiple cloning site (MCS) embedded inside the coding region of the *lacZ* gene, which codes for the $\beta$-galactosidase enzyme.
• • When foreign DNA is successfully ligated into this MCS, it interrupts the open reading frame of *lacZ*, abolishing functional enzyme production (insertional inactivation).

Bacterial colonies grown in the presence of IPTG (inducer) and X-gal (chromogenic substrate):

• • Non-recombinant colonies (no insert): The *lacZ* gene remains intact and expresses active $\beta$-galactosidase. The enzyme hydrolyzes colorless X-gal into 5-bromo-4-chloro-indigo, giving rise to BLUE colonies.
• • Recombinant colonies (with insert): Due to insertional inactivation, no active $\beta$-galactosidase is produced. The substrate is not cleaved, so colonies appear WHITE (colonies without blue colour).

Correlating with the test propositions:

• • Statement I claims blue colonies have the DNA insert. This is completely FALSE because blue colonies lack inserts.
• • Statement II claims colonies without blue colour (white colonies) have the DNA insert and are recombinants. This is completely TRUE.
• • Thus, Statement I is incorrect but Statement II is correct.

Statement I is incorrect but Statement II is correct, which corresponds to Option (4).

An alien piece of DNA transferred into an alien organism cannot replicate by itself unless it is part of a chromosome or vector having a specific sequence known as the "origin of replication" (ori).

If the alien DNA gets integrated into the recipient genome (host chromosome), it becomes part of the chromosome and gains the ability to replicate during host cell division, multiplying and segregating along with the host DNA.

Statements B (it may get integrated into the genome of the recipient) and C (it may multiply and be inherited along with host DNA) represent biologically sound outcomes described in NCERT.

Plant tissue culture is based on the cellular phenomenon that whole plants can be regenerated from explants (any part of a plant taken out and grown in a test tube under sterile conditions in a special nutrient medium).

This capacity to generate a whole plant from any cell or explant is termed totipotency, first experimentally demonstrated by Gottlieb Haberlandt and perfected by F.C. Steward using carrot phloem explants.

The first restriction endonuclease was Hind II, whose functioning depended on a specific DNA nucleotide sequence.

NCERT states: "It was found that Hind II always cut DNA molecules at a particular point by recognizing a specific sequence of six base pairs. This specific base sequence is known as the recognition sequence for Hind II."

Scientists have isolated single cells from plants and after digesting their cell walls have been able to isolate naked protoplasts (surrounded only by plasma membranes).

Isolated protoplasts from two different varieties of plants—each having a desirable character—can be fused to get hybrid protoplasts, which can be further grown to form a new plant. These hybrids are called somatic hybrids and the process is called somatic hybridization.

A classic example cited in NCERT is the fusion of a tomato protoplast with a potato protoplast to create a pomato.

Agrobacterium tumefaciens, a pathogen of several dicotyledonous plants, is able to deliver a piece of DNA (known as 'T-DNA') to transform normal plant cells into a tumor and direct these tumor cells to produce the chemicals required by the pathogen.

The extra-chromosomal DNA element responsible for this oncogenic transformation is the tumor-inducing plasmid (Ti plasmid). In genetic engineering, this plasmid has been disarmed and modified into a non-pathogenic cloning vector.

Small volume cultures cannot yield appreciable quantities of products. To produce in large quantities, the development of bioreactors, where large volumes ($100-1000$ litres) of culture can be processed, was required. Thus, bioreactors are specifically built for large-scale production, not small-scale cultures.

A bioreactor provides optimal conditions for achieving the desired product by providing optimum growth conditions (temperature, pH, substrate, salts, vitamins, oxygen). A stirred-tank reactor is usually cylindrical or with a curved base to facilitate the mixing of the reactor contents. The stirrer facilitates even mixing and oxygen availability throughout the bioreactor. Bioreactors have an agitator system, an oxygen delivery system, a foam control system, a temperature control system, pH control system and sampling ports.

Statement (1) incorrectly states that bioreactors are used for small scale cultures.

In the standard genetic map of E. coli cloning vector pBR322 illustrated in NCERT Figure 11.4: - Position X marks the 'ori' (Origin of replication). - Position Y marks the 'rop' (Repressor of primer) gene located between the tetracycline resistance cassette and the Pvu II site.

This is a sequence from where replication starts and any piece of DNA when linked to this sequence can be made to replicate within the host cells. This sequence is also responsible for controlling the copy number of the linked DNA.

The rop codes for the proteins involved in the replication of the plasmid (acting as a regulator to modulate copy number).

Option (4) provides the precise verbatim NCERT functional definitions.

Ethidium bromide ($EtBr$) is a planar polycyclic aromatic cation that slips between adjacent stacked nitrogenous base pairs of double-stranded DNA:

Intercalation isolates the ethidium fluorophore from water molecules that would otherwise quench its fluorescence. When irradiated with UV light, the complex emits intense visible fluorescence:

The separated orange DNA bands are excised from the agarose gel slab and extracted into buffer in a technique known as elution.

To obtain pure genetic material, bacterial/plant cells are digested with lysozyme/cellulase, followed by selective enzyme treatments:

Because DNA is a polyanionic macromolecule surrounded by a hydration shell of water molecules, adding cold ethanol lowers the dielectric constant, allowing monovalent cations ($Na^+$) to neutralize the phosphate backbone, precipitating DNA out of solution:

The precipitated DNA is visible as a tangle of fine white threads and is collected onto a glass rod by spooling.

Plant cells possess thick, cellulose-rich walls that resist chemical transformation (such as $CaCl_2$ heat shock). The biolistic method achieves direct physical penetration by bombarding target cells with high-momentum microprojectiles:

NCERT states verbatim: "In a method known as biolistics or gene gun, cells are bombarded with high velocity micro-particles of gold or tungsten coated with DNA."

Silver, copper, and zinc are cytotoxic heavy metals that induce oxidative stress and cell death. Gold and tungsten are biochemically inert and high-density, making them ideal carriers.

In standard molecular cloning protocols described in NCERT Section "Processes of Recombinant DNA Technology": 1. Genomic/vector DNA is cleaved with restriction endonucleases (Step B). 2. The digested mixture is resolved on agarose gel electrophoresis, and the specific desired band is isolated via elution (Step C). 3. The isolated gene of interest is amplified to billions of copies using Polymerase Chain Reaction (Step D). 4. The recombinant construct is inserted into a competent recipient host cell (Step A):

If Step C ("Isolation of desired DNA fragment") is construed broadly as the initial extraction and purification of donor cellular DNA containing the target gene: 1. Total cellular DNA containing the gene of interest is isolated (Step C). 2. DNA is subjected to restriction enzyme digestion (Step B). 3. Target gene is amplified via PCR (Step D). 4. Recombinant DNA is introduced into the host (Step A):

Because both interpretations are scientifically valid and represent sequential steps defined across different subsections of NCERT Biotechnology, NTA officially designated both Option (2) and Option (4) as correct answers in the final answer key.

A cloning vector is a self-replicating DNA molecule engineered with an origin of replication (ori), selectable markers, and unique cloning restriction sites to ferry foreign DNA into a recipient host cell:

In molecular genetics, a probe is a single-stranded stretch of DNA or RNA tagged with a radioactive molecule ($^{32}\text{P}$) or fluorophore. It is allowed to hybridize to its complementary DNA in a clone of cells followed by detection using autoradiography:

NCERT states under Molecular Diagnosis: "A single stranded DNA or RNA, tagged with a radioactive molecule (probe) is allowed to hybridise to its complementary DNA in a clone of cells followed by detection using autoradiography."

Ethidium bromide ($EtBr$) is a planar, polycyclic aromatic fluorophore that inserts (intercalates) between stacked hydrophobic nitrogenous base pairs of double-stranded DNA:

Upon intercalation into DNA's hydrophobic interior, EtBr fluorescence increases nearly 20-fold compared to free dye in aqueous solution. When irradiated with UV light, the separated DNA fragments shine distinctly as bright orange bands.

In vitro enzymatic gene amplification relies on cyclic repetition of three thermal phases:

- Denaturation: Thermal disruption converts double-stranded target DNA into two separate single strands. - Annealing: Two sets of oligonucleotide primers hybridize to their complementary flanking sequences at the $3'$ ends of each template strand. - Extension: The thermostable enzyme *Taq* DNA polymerase (isolated from *Thermus aquaticus*) extends primers along the templates in the $5' \to 3'$ direction by adding deoxynucleotides ($dNTPs$).

To obtain pure genetic material, bacterial, fungal, or plant cells are treated with specific lytic enzymes (cellulase/chitinase/lysozyme), followed by enzymatic degradation of all non-DNA polymers:

Because DNA is a highly charged polyanion with a negatively charged phosphodiester backbone, it is soluble in water. Addition of ice-cold ethanol significantly lowers the dielectric constant of the solvent, causing sodium ions to neutralize phosphate charges and forcing DNA out of aqueous solution:

The precipitated DNA aggregates into visible fine fibrous white threads that can be wound up around a glass rod in a procedure termed spooling.

Polymerase Chain Reaction (PCR) is exclusively an enzymatic DNA polymerization assay utilizing thermostable DNA polymerase, oligonucleotide primers, and deoxynucleoside triphosphates ($dNTPs$):

- Molecular diagnosis: Enables ultrasensitive early detection of infectious agents (e.g., HIV, Mycobacterium, viral hepatitis) before clinical symptoms appear. - Gene amplification: Yields microgram quantities of DNA from infinitesimal traces. - Detection of mutations: Identifies deletions, point mutations, and SNPs in suspected cancer patients and hereditary disorders.

PCR neither interacts with nor purifies proteins. Protein isolation and purification constitute downstream processing involving cell lysis, fractional centrifugation, filtration, and liquid chromatography (e.g., affinity chromatography).

Plasmid $pBR322$ has distinct unique restriction endonuclease recognition sites within selectable marker genes:

When the foreign gene encoding $\beta$-galactoside is ligated at the $PstI$ site, foreign DNA is inserted directly into the coding sequence of the $amp^R$ gene. This interruption destroys the integrity of the open reading frame, inactivating the production of functional $\beta$-lactamase enzyme:

The host *E. coli* cells transformed with the recombinant plasmid will produce $\beta$-galactoside, but will not be able to confer ampicillin resistance; they become sensitive to ampicillin and will fail to grow on medium containing ampicillin.

In vitro enzymatic gene amplification relies on cyclic repetition of three sequential, temperature-dependent stages: 1. Denaturation (approx. 94–96 °C): High thermal energy disrupts the weak hydrogen bonds holding complementary purine-pyrimidine base pairs together, unzipping double-stranded DNA (dsDNA) into two single-stranded DNA (ssDNA) templates. 2. Annealing (approx. 50–60 °C): Temperature is lowered to enable synthetic oligonucleotide primers to hybridize specifically to complementary flanking sequences at the $3'$ ends of ssDNA. 3. Extension (approx. 72 °C): Thermostable *Taq* DNA polymerase (isolated from thermophilic bacterium *Thermus aquaticus*) adds deoxynucleotide triphosphates (dNTPs) onto the $3'\text{-OH}$ primer ends in the $5' \to 3'$ direction.

Because denaturation is the initial gatekeeper step requiring maximum thermal energy (~94 °C), failure to reach or maintain high temperature prevents the separation of double-stranded DNA into single strands. Consequently, the primer target sites remain buried within duplex DNA. Hence, Denaturation is the very first step affected.

Restriction endonucleases (Type II restriction enzymes) serve as precision "molecular scissors" in genetic engineering: - The enzyme scans duplex DNA until it locates its specific recognition sequence (typically 4 to 8 base pairs in length). - These recognition sequences are palindromes with rotational dyad symmetry: the sequence of base pairs reads identical when reading both antiparallel strands in the same orientation (either $5' \to 3'$ or $3' \to 5'$). - For example, the restriction endonuclease *Eco*RI recognizes the 6-base pair palindrome: $$\begin{aligned} 5'-\text{G A A T T C}-3' \\ 3'-\text{C T T A A G}-5' \end{aligned}$$ - *Eco*RI cuts both strands between the G and A bases, generating overhanging, complementary single-stranded ends termed sticky ends.

- Degenerate primer sequence: Oligonucleotide primer mixtures used in PCR when target sequences exhibit codon redundancy, not restriction sites. - Okazaki fragments / sequences: Short lagging-strand DNA segments synthesized discontinuously during semi-conservative DNA replication. - Poly(A) tail sequences: A stretch of 200–300 adenylate residues added post-transcriptionally to the $3'$ end of eukaryotic pre-mRNA for stability and nuclear export.

Genetic engineering utilizes precision biocatalysts with specific substrates and chemical actions: - DNA Ligases: Catalyze the formation of a covalent phosphodiester bond between the $3'\text{-OH}$ end of one DNA strand and the $5'\text{-phosphate}$ group of another, effectively joining/sealing two DNA molecules together. - DNA Polymerases: Catalyze the $5' \to 3'$ template-dependent condensation of deoxynucleoside triphosphates (dNTPs) to synthesize new complementary strands (not breaking DNA). - Helicases: Unwind and separate the complementary base-paired strands of duplex DNA by breaking hydrogen bonds (not nucleases). - Exonucleases: Hydrolyze phosphodiester bonds at the terminal ends ($5'$ or $3'$) of a polynucleotide chain, removing one nucleotide at a time. - Endonucleases (Restriction Enzymes): Cleave phosphodiester bonds at specific internal recognition sites within the DNA molecule.

Only pair (1) matches the enzyme with its genuine biochemical function.