Biotechnology: Principles and Processes MCQs

Identify the gene of interest that confers the desired trait.

Insert the isolated DNA into the host cell using vectors or physical methods.

Ensure the introduced DNA is maintained and passed to progeny cells.

Denaturation of all host proteins by heat is not a required step, so it is not part of the basic process.

Sticky ends are short single‑stranded overhangs left after a restriction enzyme cuts DNA.

These complementary overhangs can anneal with matching sequences on another DNA fragment.

DNA ligase then forms phosphodiester bonds between the adjacent nucleotides, sealing the nicks.

Thus the enzyme that acts on sticky ends during rDNA formation is DNA ligase.

Beta‑galactosidase cleaves a colourless chromogenic substrate (X‑gal) to release a blue product. In blue‑white screening, colonies with an intact lacZ gene turn blue, while disrupted lacZ gives white colonies. The blue colour therefore comes from the chromogenic substrate acted on by the enzyme. Chromogenic substrate.

A disarmed pathogen vector is a virus whose disease‑causing genes have been removed but retains its natural ability to enter host cells.

When it infects a cell, the viral coat delivers the recombinant DNA carried inside the vector into the host cytoplasm or nucleus.

Thus DNA transfer occurs through infection rather than chemical or physical methods.

Denaturation: heat the DNA to separate the double strands into single strands.

Annealing: cool the reaction so primers can bind (anneal) to their complementary sequences on the single‑stranded templates.

Extension: raise the temperature to the optimal level for DNA polymerase to synthesize new DNA strands from the primers.

Thus the cycle proceeds as denaturation, annealing, extension.

Restriction enzymes cut DNA at specific sites; some cleave both strands at different positions.

When the cuts are offset, each strand leaves a short unpaired segment.

These unpaired segments can anneal with complementary sequences, so they are called sticky ends.

During blue‑white screening the host strain has a functional lacZ gene that produces β‑galactosidase, turning X‑gal blue.

Insertion of a DNA fragment into the multiple‑cloning site disrupts lacZ, so the recombinant plasmid cannot cleave X‑gal.

Thus colonies with recombinant plasmids remain colourless (white) while non‑recombinants turn blue.

Answer: White.

Microinjection involves using a fine glass needle to introduce DNA directly into a cell.

The needle can be positioned to penetrate the plasma membrane and reach the nucleus, ensuring the recombinant DNA reaches the nuclear compartment.

Because the DNA is physically delivered into the nucleus, it bypasses the need for vectors or membrane permeabilization.

Thus the method is “Directly injected into the nucleus of an animal cell.”

DNA is amplified by repeatedly heating and cooling the sample.

A thermostable DNA polymerase extends primers that flank the target region.

The process is called the polymerase chain reaction.

Agarose forms a porous gel when dissolved in buffer and solidified, allowing DNA fragments to migrate according to size. Its pore size can be adjusted for the range of fragment lengths typically analyzed. Unlike cellulose or starch, agarose does not interact with DNA and provides clear bands. Hence the matrix commonly used is agarose.

The first recombinant DNA was created by inserting the tetracycline resistance gene into a plasmid vector.

The plasmid used was pBR322, which was originally isolated from a strain of Salmonella typhimurium.

Joining the resistance gene with this Salmonella‑derived plasmid allowed replication in E. coli hosts.

Thus the correct bacterium is Salmonella typhimurium.

Both vector and foreign DNA are cut to produce compatible sticky ends.

Using the same restriction enzyme generates identical over‑hangs that can anneal correctly.

These complementary ends allow the DNA ligase to join the fragments efficiently.

Therefore the vector and foreign DNA must be cut with the same restriction enzyme.

Agrobacterium tumefaciens transfers a segment of its Ti (tumour‑inducing) plasmid into plant cells, causing crown‑gall disease.

The T‑DNA region of the Ti plasmid can be engineered to carry foreign genes while retaining the plant‑integration machinery.

Thus the modified Ti plasmid serves as a vector for stable gene transfer and expression in plants.

First isolate the gene of interest from the source organism.

Then use restriction enzymes to cut both the gene and the plasmid vector at matching sites.

Next ligate the gene into the opened vector forming recombinant DNA.

Finally introduce the recombinant plasmid into host cells by transformation. Isolation of DNA → cutting with restriction enzymes → ligation into vector → transformation

In PCR the DNA region to be amplified is flanked by short single‑stranded DNA pieces that bind (anneal) to the target sequence.

These synthetic oligonucleotides provide a free 3′‑OH for DNA polymerase to extend the new strand.

Since they are designed to be complementary to the template regions, they are called primers.

Recombinant DNA involves cutting DNA with restriction enzymes and joining it to a plasmid vector.

Cohen demonstrated the transfer of a gene from one bacterium to another using plasmids, and Boyer developed the method to splice DNA fragments and clone them in E. coli.

Their 1973 experiments created the first genetically engineered bacteria, establishing recombinant DNA technology.

Thus the correct pair is Stanley Cohen and Herbert Boyer.

Restriction enzymes cut only unmethylated DNA; the host bacterium methylates its own recognition sites.

The enzyme that adds methyl groups to specific bases is modification methylase.

Methylated host DNA is not recognized as foreign, so it is protected from cleavage.

Hence the correct answer is Modification methylase.

Agrobacterium tumefaciens carries a Ti plasmid whose T‑DNA segment integrates into the host genome.

During infection the bacterium injects this T‑DNA into a wounded plant cell through a type‑IV secretion system.

The transferred genes encode enzymes for auxin and cytokinin synthesis, causing uncontrolled cell division and crown‑gall formation.

Thus the bacterium naturally transforms normal plant cells into a tumour.

Lysozyme hydrolyzes the β‑1,4‑glycosidic bonds in peptidoglycan, the main component of bacterial cell walls.

Breaking the peptidoglycan layer weakens the wall, allowing the membrane to rupture and release DNA.

Thus lysozyme is the enzyme used with a lysis buffer for bacterial DNA isolation. Lysozyme.

DNA polymerase that can withstand the high denaturation temperature (~95 °C) is required for PCR cycles.

Thermostable enzymes are isolated from thermophilic bacteria that live at high temperatures.

The bacterium *Thermus aquaticus* yields a DNA polymerase that remains active after repeated heating.

Thus the heat‑stable enzyme used in PCR is Taq polymerase.