Process of Recombinant DNA technology Questions in English

(C) In the replica plating experiment,the master plate contains a mixture of different bacterial colonies,including both drug-resistant and non-resistant strains.
This plate serves as the original source from which replicas are made onto other plates containing specific selective media (e.g.,media with antibiotics).
By comparing the growth on the selective plates with the master plate,researchers can identify specific colonies that possess the trait of drug resistance.

(C) The first recombinant $DNA$ molecule was constructed in $1973$ by Stanley Cohen and Herbert Boyer. They accomplished this by isolating an antibiotic resistance gene and linking it with a native plasmid of $Salmonella$ $typhimurium$. This recombinant plasmid was then successfully introduced (inoculated) into $E. coli$ using transformation techniques,marking the birth of modern biotechnology.

(B) The technique of inserting a desired gene into the $DNA$ of a plasmid vector is called gene cloning or recombinant $DNA$ technology.
In this process,the target gene is inserted into a vector (like a plasmid) to create a recombinant $DNA$ molecule,which is then introduced into a host organism for replication and expression.
Therefore,the correct term among the given options is cloning.

(D) The biotechnological production of antibiotics involves several critical steps.
First,it is essential to identify and screen for microorganisms that naturally produce antibiotic compounds.
Second,the specific gene responsible for the synthesis of the antibiotic must be isolated from the organism.
Third,this gene is inserted into a vector,such as an $E. coli$ plasmid,to create recombinant $DNA$,which is then introduced into a host cell for large-scale production.
Therefore,all the listed options are necessary prerequisites for this process.

(C) The process of joining different $DNA$ fragments together is known as gene splicing. This is a fundamental step in recombinant $DNA$ technology,where specific $DNA$ sequences are linked to a vector or another $DNA$ molecule using enzymes like $DNA$ ligase.

(C) The transfer of proteins from a polyacrylamide gel electrophoresis $(PAGE)$ onto a nitrocellulose or nylon membrane is known as Western blotting.
Northern blotting is a technique used for the transfer and detection of $RNA$ molecules.
Southern blotting is a technique used for the transfer and detection of $DNA$ molecules.

(D) The Southern Blot technique is a method used for detection of a specific $DNA$ sequence in $DNA$ samples.
$1$. The first step in this process is the isolation of $DNA$ from a nucleated cell (e.g.,blood,hair follicle,or skin cells).
$2$. Once isolated,the $DNA$ is digested using restriction endonucleases.
$3$. The resulting fragments are separated by gel electrophoresis.
$4$. The separated $DNA$ fragments are then denatured and transferred onto a nylon or nitrocellulose membrane.
$5$. Finally,the membrane is hybridized with a labeled probe to detect the target sequence.

(A) Southern blotting is a molecular biology technique used for the detection of specific $DNA$ sequences in $DNA$ samples.
In this process,$DNA$ fragments are separated by gel electrophoresis and then transferred to a membrane (blotting) to be identified using a labeled probe.
Therefore,the correct option is $A$.

(B) $PCR$ (Polymerase Chain Reaction) is a laboratory technique used to amplify a specific segment of $DNA$ molecule.
It allows for the generation of millions of copies of a target $DNA$ sequence from a very small sample.
This process eliminates the need for time-consuming cloning procedures in bacteria.

(C) The Hepatitis $B$ vaccine is a recombinant vaccine produced using recombinant $DNA$ technology.
It is classified as a second-generation vaccine because it is produced by expressing the viral antigen (surface antigen of the Hepatitis $B$ virus) in a host organism like yeast ($Saccharomyces$ $cerevisiae$).
First-generation vaccines are typically whole-pathogen vaccines (inactivated or attenuated),whereas second-generation vaccines use specific subunits or recombinant proteins.

(D) The Southern Blotting technique is a method used for detection of specific $DNA$ sequences in $DNA$ samples.
The steps involved are:
$1$. Isolation of $DNA$ from the sample (e.g., blood, hair, or crime scene evidence).
$2$. Digestion of $DNA$ using restriction endonucleases.
$3$. Separation of $DNA$ fragments by gel electrophoresis.
$4$. Transfer (blotting) of separated $DNA$ fragments to a synthetic membrane (nitrocellulose or nylon).
$5$. Hybridization using a labeled probe.
$6$. Detection of hybridized fragments using autoradiography.
Therefore, the first step is the isolation of $DNA$ from the source.

(C) The basic steps in creating a Genetically Modified Organism $(GMO)$ or recombinant $DNA$ technology are:
$1$. Identification of $DNA$ with desirable genes.
$2$. Introduction of the identified $DNA$ into the host.
$3$. Maintenance of introduced $DNA$ in the host and transfer of the $DNA$ to its progeny.
Amplification of $DNA$ using $PCR$ is a technique used to increase the number of copies of a specific $DNA$ segment,but it is not a mandatory step in the general process of creating a $GMO$,as the gene can be isolated and inserted directly if sufficient quantity is available.

(D) Gel electrophoresis is a technique used to separate $DNA$ fragments based on their size.
$DNA$ molecules are negatively charged due to the phosphate groups in their sugar-phosphate backbone.
When an electric field is applied,the $DNA$ fragments move towards the positive electrode (anode).
Therefore,the samples are loaded into the wells located at the negative electrode (cathode) end so that they can migrate through the gel matrix towards the positive end.

(D) $PCR$ (Polymerase Chain Reaction) is a technique used to amplify specific $DNA$ sequences.
It is widely used in forensic science to identify criminals by amplifying $DNA$ samples found at crime scenes.
It is also essential in the production of transgenic organisms and genetically modified food by allowing researchers to isolate and amplify specific genes of interest for insertion into host genomes.
Therefore,$PCR$ is useful in all the mentioned fields.

(C) $PCR$ (Polymerase Chain Reaction) is a technique used to amplify a specific segment of $DNA$.
The essential components required for $PCR$ are:
$1$. $DNA$ template: The target $DNA$ sequence to be amplified.
$2$. Primers: These are small,chemically synthesized oligonucleotides that are complementary to the regions of $DNA$. In $PCR$,$DNA$ primers are used,not $RNA$ primers (which are used in natural $DNA$ replication).
$3$. $Taq$ polymerase: $A$ thermostable $DNA$ polymerase enzyme that synthesizes the new $DNA$ strand.
$4$. Deoxynucleotide triphosphates $(dNTPs)$: Building blocks for the new $DNA$ strand.
Therefore,$RNA$ primer is not required for $PCR$.

(C) Electroporation is a technique used in genetic engineering.
In this process,cells are exposed to a short,high-voltage electrical pulse.
This creates temporary pores in the cell membrane,through which foreign $DNA$ or other molecules can easily enter the cell.
Therefore,the correct option is $C$.

(B) In a continuous culture system,the cells are maintained in the log phase (exponential phase) of growth,not the lag phase.
In this system,the used medium is drained out from one side while fresh medium is added from the other to maintain the cells in their physiologically most active phase.
This type of culture system produces a larger biomass and leads to higher yields of the desired protein or product.

(D) Direct gene transfer,also known as physical gene transfer,involves introducing foreign $DNA$ directly into the host cell without the use of a vector.
$1$. Microinjection: $DNA$ is directly injected into the nucleus of an animal cell using a fine glass needle.
$2$. Electroporation: High-voltage electrical pulses are used to create temporary pores in the cell membrane,allowing $DNA$ to enter.
$3$. Biolistics (Gene gun): Microscopic particles of gold or tungsten coated with $DNA$ are bombarded into target cells.
Since all three methods are techniques for direct gene transfer,the correct answer is $D$.

(B) In $r-DNA$ technology,various methods are used to introduce recombinant $DNA$ into host cells.
$1$. Transformation: The process by which a cell takes up naked $DNA$ from the environment.
$2$. Electroporation: $A$ technique that uses electrical pulses to create temporary pores in the cell membrane to allow $DNA$ entry.
$3$. Transduction: The process by which foreign $DNA$ is introduced into a cell by a virus or viral vector.
$4$. Conjugation is a natural process of genetic transfer between bacteria through direct cell-to-cell contact,which is not a standard laboratory technique used for introducing engineered $r-DNA$ into a host cell in the context of $r-DNA$ technology protocols.
Therefore,the correct answer is $B$.

(B) In a sparged stirred-tank bioreactor,sterile air is bubbled through the reactor.
These air bubbles not only provide oxygen to the culture but also increase the oxygen transfer surface area,which enhances the growth and metabolic activity of the microorganisms.

(B) In $r-DNA$ technology,specifically during gel electrophoresis,the separated $DNA$ fragments are visualized under $UV$ light after staining with ethidium bromide.
The process of cutting out the desired $DNA$ band from the agarose gel and extracting the $DNA$ from the gel piece is known as 'elution'.
This purified $DNA$ is then used in constructing recombinant $DNA$ by joining it with cloning vectors.

(A) Transformation is a fundamental process in biotechnology where a host organism,typically a bacterium,takes up foreign genetic material $(DNA)$ from its surroundings.
This process allows the host cell to express the genes present on the introduced $DNA$ molecule.
Therefore,the correct definition is that a piece of $DNA$ is introduced into a host bacterium.

(B) Gel electrophoresis is a technique used to separate $DNA$ fragments based on their size.
When $DNA$ is treated with restriction enzymes,it is cut into fragments of different lengths.
To verify whether the digestion process has occurred successfully and to check the size of the resulting $DNA$ fragments,the sample is loaded onto an agarose gel and subjected to an electric field.
This allows the separation of $DNA$ fragments,which can then be visualized to confirm the completion of the digestion.

(C) The ampicillin resistance gene acts as a selectable marker in recombinant $DNA$ technology.
When a recombinant $DNA$ molecule carrying this gene is introduced into $E. coli$ cells,the cells that successfully take up the $DNA$ become 'transformed'.
These transformed cells acquire resistance to the antibiotic ampicillin.
When these cells are plated on an agar medium containing ampicillin,only the transformed cells can survive and form colonies,while the untransformed cells (which lack the resistance gene) are killed by the antibiotic.

(C) $PCR$ stands for Polymerase Chain Reaction.
It is a laboratory technique used to amplify specific segments of $DNA$.
Through multiple cycles of denaturation,annealing,and extension,$PCR$ produces millions of copies of a target $DNA$ sequence from a small initial sample.

(D) Biolistics or gene gun method is a direct gene transfer technique.
In this method,cells are bombarded with high-velocity micro-particles of gold or tungsten coated with $DNA$.
This technique is specifically used for the transformation of plant cells,where the cell wall acts as a barrier to other methods of gene transfer.

(B) $Polyethylene \text{ } Glycol$ $(PEG)$ is a chemical agent used in plant tissue culture and biotechnology to facilitate the direct uptake of foreign $DNA$ into protoplasts. This process is known as direct gene transfer or vectorless gene transfer, as it does not require a biological vector like $Agrobacterium \text{ } tumefaciens$ to introduce the genetic material into the host cell.

(B) The process of insertional inactivation is used to distinguish recombinant from non-recombinant colonies.
When the $lacZ$ gene is inserted with a foreign $DNA$ sequence,the enzyme $\beta$-galactosidase is not produced.
In the presence of a chromogenic substrate,non-recombinant bacteria produce blue-colored colonies because the $\beta$-galactosidase enzyme is functional.
However,in recombinant bacteria,the $lacZ$ gene is inactivated,so the enzyme is not produced,and the colonies appear colorless (white).

(A) $PCR$ (Polymerase Chain Reaction) involves three main steps:
$1$. Denaturation: The double-stranded $DNA$ is heated to a high temperature (approx. $94-98^{\circ}C$) to separate the strands.
$2$. Annealing: The temperature is lowered (approx. $50-65^{\circ}C$) to allow primers to bind to the single-stranded $DNA$ templates.
$3$. Extension: The temperature is adjusted (approx. $72^{\circ}C$) for the $Taq$ $DNA$ polymerase to synthesize the new $DNA$ strand by adding nucleotides.
Therefore,the correct sequence is Denaturation,Annealing,and Extension.

(C) The Polymerase Chain Reaction $(PCR)$ is a laboratory technique used to make multiple copies of a specific segment of $DNA$.
It allows scientists to take a very small sample of $DNA$ and amplify it to a large enough amount to study in detail.
Therefore,the primary purpose of $PCR$ is $DNA$ amplification.

(C) The number of $DNA$ copies produced in $PCR$ after $n$ cycles is given by the formula $2^n$,where $n$ is the number of cycles.
Given that the number of cycles $n = 6$.
Therefore,the number of $DNA$ copies = $2^6 = 2 \times 2 \times 2 \times 2 \times 2 \times 2 = 64$.
Thus,after $6$ cycles,$64$ copies of the $DNA$ sample will be obtained.

(B) Thermal cycling is the fundamental process used in the Polymerase Chain Reaction $(PCR)$.
It involves repeated cycles of heating and cooling the reaction mixture to specific temperatures.
These cycles consist of three main steps: $1.$ Denaturation (at high temperature,$\approx 94-98^{\circ}C$),$2.$ Annealing (at lower temperature,$\approx 50-65^{\circ}C$),and $3.$ Extension (at optimal temperature for $DNA$ polymerase,$\approx 72^{\circ}C$).
This process allows for the exponential amplification of a specific $DNA$ segment.

(C) The $PCR$ (Polymerase Chain Reaction) process consists of three main steps:
$1$. $Denaturation$: The double-stranded $DNA$ is heated to a high temperature (approx. $94-98^{\circ}C$) to separate the strands.
$2$. $Annealing$: The temperature is lowered (approx. $50-65^{\circ}C$) to allow primers to bind to the single-stranded $DNA$ templates.
$3$. $Extension$: The temperature is adjusted (approx. $72^{\circ}C$) for the $Taq$ polymerase enzyme to synthesize the new $DNA$ strand by adding nucleotides.
Therefore, the correct sequence is $Denaturation \rightarrow Annealing \rightarrow Extension$.

(C) In biotechnology,specifically during the process of microbial culture or fermentation,the inoculum requires a constant temperature to ensure optimal growth and metabolic activity of the microorganisms. The standard temperature maintained for most mesophilic microorganisms,such as $E. coli$,is $37^oC$. This temperature mimics the physiological conditions of the host environment,allowing for efficient protein expression and cellular replication.

(B) Micro-injection is a technique used to introduce foreign $DNA$ directly into the nucleus of an animal cell using a fine glass micropipette. This method is commonly used in animal cells because they lack a rigid cell wall,making them suitable for direct injection. In contrast,the gene gun method is primarily used for plant cells.

(C) Downstream processing is a critical stage in biotechnology that occurs after the biosynthesis phase (the fermentation or bioreactor process).
It involves the processes required to prepare the biosynthetic products for marketing.
The two primary steps involved in downstream processing are:
$1$. Separation: Isolating the product from the culture medium or cells.
$2$. Purification: Removing impurities to obtain the final product in a pure form.
Therefore,separation and purification are collectively referred to as downstream processing.

(B) In agarose gel electrophoresis,$DNA$ fragments are separated based on their size.
$DNA$ molecules are negatively charged and are not visible under normal visible light.
To visualize the $DNA$ fragments,the gel must be stained with a fluorescent dye such as ethidium bromide $(EtBr)$.
Once stained,the $DNA$ can be observed as bright orange-colored bands when exposed to $U.V.$ radiation.
Therefore,the correct statement is that $DNA$ can be seen with staining in $U.V.$ radiation.

(B) In recombinant $DNA$ technology,the selection of recombinants is often done using the principle of insertional inactivation.
When a recombinant $DNA$ is inserted into the coding sequence of an enzyme,such as $\beta$-galactosidase,the enzyme becomes inactivated.
This is known as insertional inactivation.
When a chromogenic substrate is added to the medium,non-recombinant colonies (containing the functional enzyme) produce a blue colour.
In contrast,recombinant colonies (where the enzyme is inactivated) do not produce the enzyme,and therefore,they appear white.

(D) Restriction endonucleases cut $DNA$ at specific recognition sequences,resulting in fragments of varying lengths.
These $DNA$ fragments are negatively charged due to the phosphate backbone.
They can be separated based on their size by a technique called gel electrophoresis.
In this technique,the $DNA$ fragments are forced to move towards the anode under an electric field through a matrix (usually agarose gel).
The smaller fragments move faster and travel further through the gel matrix compared to larger fragments.

(C) Gel electrophoresis is a technique used to separate $DNA$ fragments based on their size.
In this process,$DNA$ fragments are loaded into an agarose gel matrix.
When an electric current is applied,the negatively charged $DNA$ molecules move towards the anode.
The gel acts as a molecular sieve,where smaller fragments move faster and travel further through the pores of the gel,while larger fragments move more slowly.
Therefore,the separation is primarily based on the molecular size of the $DNA$ fragments.

(D) The gene gun method,also known as biolistics or microprojectile bombardment,is a technique used to introduce foreign $DNA$ into plant cells.
In this method,cells are bombarded with high-velocity micro-particles of gold or tungsten coated with $DNA$.
These heavy metal particles are used because they are inert and do not cause toxicity to the plant cells.
Therefore,the correct option is $D$.

(C) The technique used to amplify a specific segment of $DNA$ in vitro is known as the Polymerase Chain Reaction $(PCR)$.
In this process,multiple copies of the gene of interest are synthesized in vitro using two sets of primers and the enzyme $DNA$ polymerase.
The enzyme extends the primers using the nucleotides provided in the reaction and the genomic $DNA$ as a template.
If the process of replication is repeated many times,the segment of $DNA$ can be amplified to approximately billion times.

(C) Bioreactors are vessels in which raw materials are biologically converted into specific products by microbes,plant,animal,or human cells.
They are designed to provide optimal conditions for achieving the desired product by providing optimum growth conditions such as temperature,$pH$,substrate,salts,vitamins,and oxygen.
Bioreactors are essential for the processing of large volumes of culture to produce large quantities of products like enzymes,antibiotics,or recombinant proteins on an industrial scale.

(C) To make a bacterium competent to take up recombinant $DNA$,it is treated with a specific concentration of a divalent cation,such as calcium $(Ca^{2+})$.
This treatment increases the efficiency with which $DNA$ enters the bacterium through pores in its cell wall.
Therefore,the correct option is $C$.

(C) $DNA$ molecules are negatively charged due to the presence of phosphate groups in their sugar-phosphate backbone.
During the process of gel electrophoresis,$DNA$ fragments are placed in an electric field.
Because $DNA$ is negatively charged,it is attracted towards the anode,which is the positively charged electrode.
Therefore,$DNA$ molecules are translocated towards the positive charge.

(A) In gel electrophoresis,$DNA$ fragments are separated based on their size through an agarose gel matrix.
Once the separation is complete,the $DNA$ bands are visualized under $UV$ light.
The specific $DNA$ fragments of interest are then cut out from the agarose gel.
The process of extracting these $DNA$ fragments from the gel piece is known as $Elution$.

(C) Bacterial cells do not take up recombinant $DNA$ easily because $DNA$ is a hydrophilic molecule and cannot pass through cell membranes.
To force bacteria to take up the $DNA$,they are first treated with a specific concentration of a divalent cation,such as calcium $(Ca^{2+})$,which increases the efficiency with which $DNA$ enters the bacterium through pores in its cell wall.
Recombinant $DNA$ can then be forced into such cells by incubating the cells with recombinant $DNA$ on ice,followed by placing them briefly at $42^{\circ}C$ (heat shock),and then putting them back on ice.
This heat shock enables the bacteria to take up the recombinant $DNA$ through transient pores created in the cell wall.

(C) $DNA$ is a negatively charged,hydrophilic molecule,which prevents it from passing through the hydrophobic lipid bilayer of the cell membrane.
To facilitate the uptake of recombinant $DNA$ by host cells like bacteria,they must be made 'competent'.
Competency is achieved through various methods,such as treatment with divalent cations (e.g.,$Ca^{2+}$) or heat shock,which increases the efficiency with which $DNA$ enters the bacterium through pores in its cell wall.
Therefore,both statements $I$ and $II$ are scientifically correct.

(D) Gel electrophoresis is a technique used to separate $DNA$ fragments based on their size.
$I.$ Ethidium bromide $(EtBr)$ is used to stain $DNA$ fragments so they can be visualized under $UV$ light.
$II.$ Restriction endonucleases are used to cut $DNA$ into fragments before electrophoresis.
$III.$ Agarose is a natural polymer extracted from seaweeds that forms the gel matrix used for separation.
$IV.$ $UV$ radiation is used to visualize the $DNA$ bands stained with ethidium bromide.
Since all these components are essential parts of the process of gel electrophoresis and $DNA$ visualization,the correct option is $I, II, III$ and $IV$.

(B) The $PCR$ ($Polymerase$ $Chain$ $Reaction$) technique requires a thermostable $DNA$ polymerase enzyme to withstand the high temperatures used during the denaturation step.
$Taq$ $DNA$ polymerase is derived from the thermophilic bacterium $Thermus$ $aquaticus$,which makes it highly thermostable.
Therefore,the statement that '$Taq$ $DNA$ polymerase is not thermostable' is incorrect.