Tools of recombinant DNA technology Questions in English

(B) helper virus is a virus that provides the necessary functions or components that are missing in a defective virus,allowing the defective virus to replicate and produce progeny. Therefore,a helper virus is often required by a defective phage to complete its life cycle.

(C) Plasmids are small,circular,double-stranded $DNA$ molecules that are distinct from a cell's chromosomal $DNA$.
They are naturally found in bacterial cells and some eukaryotes like yeast.
Plasmids are considered extra-chromosomal genetic material because they replicate independently of the chromosomal $DNA$.
They often carry genes that provide advantages to the host,such as antibiotic resistance.

(B) genetic vector is a $DNA$ molecule used as a vehicle to artificially carry foreign genetic material into another cell,where it can be replicated and/or expressed.
Both $Phage$ (bacteriophage) and $Plasmid$ are commonly used as cloning vectors in genetic engineering.
However,in the context of standard biology multiple-choice questions where only one option is typically selected,both $A$ and $B$ are correct. If the question implies the most common laboratory tool,$Plasmid$ is frequently cited.

(B) The replication of plasmid $DNA$ is an autonomous process that occurs independently of the chromosomal $DNA$ replication of the host bacterium.
While the initiation of replication is often regulated by specific plasmid-encoded proteins (such as Rep proteins) that interact with the origin of replication $(oriV)$,the subsequent elongation and termination phases of plasmid $DNA$ replication are primarily mediated by the host cell's machinery.
Therefore,the host bacterial genes provide the necessary enzymes and factors (such as $DNA$ polymerase,helicase,and primase) to carry out the replication process.

(D) The correct answer is $(d)$.
Plasmids are small,circular,extrachromosomal $DNA$ molecules found in bacteria that are used as vectors in genetic engineering.
They are ideal carriers because they possess an origin of replication $(ori)$,which allows them to replicate independently within the host cell.
Furthermore,they have the capacity to integrate or bind with foreign $DNA$ (such as eukaryotic $DNA$) to form recombinant $DNA$,which can then be introduced into a host organism for cloning or expression.

(D) $Agrobacterium \text{ } tumefaciens$ is known as the natural genetic engineer of plants.
It is a soil-borne bacterium that naturally infects plants and transfers a specific segment of its $DNA$, known as $T-DNA$ (Transfer $DNA$), from its $Ti$ (Tumor inducing) plasmid into the host plant genome.
This ability to transfer genes into plants makes it a powerful tool in biotechnology for creating transgenic plants.

(A) The $K_{12}$ strain of $E. coli$ was the first to be studied for its genetic properties,notably by American scientists Joshua Lederberg and Edward Tatum in $1946$. This landmark study demonstrated bacterial conjugation,which is a process of genetic transfer mediated by plasmids.

(D) The interaction between $Agrobacterium$ $tumefaciens$ and plants is the most thoroughly studied bacteria-plant interaction.
$Agrobacterium$ $tumefaciens$ is a soil bacterium that causes crown gall disease in many dicotyledonous plants.
It is widely used in genetic engineering as a natural vector for gene transfer because it can transfer a segment of its $DNA$,known as $T$-$DNA$,into the host plant genome,causing the formation of galls (tumors).

(A) $W. Arber$ and $D. Nathans$ were awarded the Nobel Prize in $1978$ for the discovery of restriction endonucleases,which are enzymes that cleave $DNA$ at specific sites.

(A) Plasmids are small, circular, double-stranded $DNA$ molecules that are distinct from a cell's chromosomal $DNA$.
They are naturally found in bacteria and some eukaryotes.
Due to their ability to replicate independently and carry foreign genes, they are extensively used as vectors in genetic engineering to transfer genetic material into host cells.
Because of this versatile role in biotechnology, they are often referred to as "magic circles".

(C) plasmid is an extra-chromosomal,circular $DNA$ molecule found in bacteria and some eukaryotes.
It possesses its own origin of replication,which allows it to replicate independently of the host cell's chromosomal $DNA$.

(C) Plasmids are small,extrachromosomal,self-replicating,circular,double-stranded $DNA$ molecules found primarily in bacteria. They are distinct from the chromosomal $DNA$ of the cell and often carry genes that provide advantages such as antibiotic resistance.

(C) $DNA$ ligase is known as the polynucleotide joining enzyme.
It catalyzes the formation of phosphodiester bonds between adjacent nucleotides.
This enzyme is essential for joining $DNA$ fragments,such as Okazaki fragments during replication,and for sealing nicks in the $DNA$ backbone during repair processes.

(C) Restriction enzymes are a class of enzymes that act as molecular scissors.
They recognize specific nucleotide sequences in a $DNA$ molecule,known as recognition sites,and cleave the phosphodiester backbone at these specific locations to produce $DNA$ segments.
$DNA$ polymerase is involved in $DNA$ replication,$DNA$ ligase acts as a molecular glue to join $DNA$ fragments,and $DNA$ gyrase is involved in relieving supercoiling during $DNA$ replication.

(D) Restriction endonucleases are enzymes that are specialized to cut $DNA$ at specific sites in regions having palindromic sequences. These enzymes act as molecular scissors to create recombinant $DNA$ molecules.

(C) The correct answer is $(c)$.
Endonucleases are enzymes that cut $DNA$ at specific,desired locations.
Because they act as molecular scissors to cleave the $DNA$ backbone,they are commonly referred to as the chemical knives of $DNA$.

(C) Restriction endonucleases are enzymes that cut $DNA$ at specific recognition sequences.
They are naturally produced by bacteria as a defense mechanism against bacteriophages.
In the field of biotechnology,they are essential tools used in genetic engineering to create recombinant $DNA$ molecules by cutting $DNA$ at precise locations.

(B) The restriction enzyme $Eco\ RI$ recognizes a specific palindromic nucleotide sequence in $DNA$ and cuts it.
The recognition sequence for $Eco\ RI$ is $5'-GAATTC-3'$ on one strand and $3'-CTTAAG-5'$ on the complementary strand.
Therefore,the correct sequence is:
$\mathop {{\text{GAATTC}}}\limits_{{\text{CTTAAG}}} $

(C) $c-DNA$ (complementary $DNA$) is synthesized from an $mRNA$ template.
This process is known as reverse transcription.
The enzyme responsible for this process is reverse transcriptase,which is also known as $RNA$ dependent $DNA$ polymerase.
Therefore,the correct option is $C$.

(C) The correct answer is $C$.
Endonucleases are enzymes that cleave the phosphodiester bonds within a polynucleotide chain.
Unlike exonucleases,which remove nucleotides from the ends of the chain,endonucleases act on internal sites.
Restriction endonucleases are a specific type of endonuclease that recognize and cut $DNA$ at specific internal sequences.

(D) $Taq$ polymerase is used to make numerous identical copies of a desired $DNA$ segment by polymerase chain reaction $(PCR)$.
It is a thermostable enzyme isolated from the bacterium $Thermus$ $aquaticus$, which can withstand high temperatures of $90^{\circ}C$ or more during the denaturation step of $PCR$.

(D) Transducing phages are bacteriophages that carry bacterial $DNA$ from one bacterium to another during the process of transduction.
Most bacteriophages,including those involved in generalized and specialized transduction (such as $T4$ or $Lambda$ phage),possess a double-stranded $DNA$ $(dsDNA)$ genome.
Therefore,the correct answer is double-stranded $DNA$.

(D) The interaction between $Agrobacterium$ $tumefaciens$ and plants is the most thoroughly studied bacteria-plant interaction. $Agrobacterium$ $tumefaciens$ is a soil pathogen that causes crown gall disease in many dicotyledonous plants. It is widely used in genetic engineering as a natural vector for gene transfer because it can transfer a specific segment of $DNA$, known as $T-DNA$, from its Ti plasmid into the host plant genome.

(C) $Agrobacterium \text{ } tumefaciens$ is a soil bacterium that naturally infects a wide variety of dicot plants.
It contains a $Ti$ (tumor-inducing) plasmid, which it uses to transfer a specific segment of $DNA$, known as $T-DNA$, into the host plant's genome.
Because of this unique ability to naturally transfer and integrate its own genes into the host plant's genome, it is widely referred to as a 'natural genetic engineer' in the field of biotechnology.

(C) Plasmids are small,circular,double-stranded $DNA$ molecules that are distinct from a cell's chromosomal $DNA$.
They are naturally found in bacteria and are widely used as cloning vectors in genetic engineering because they can replicate independently within the host cell and carry foreign $DNA$ fragments.

(A) In genetic engineering,foreign $DNA$ and plasmid $DNA$ are joined with the help of the $DNA$ ligase enzyme to form recombinant $DNA$. This enzyme acts as a molecular glue,making it indispensable for the construction of recombinant $DNA$ molecules.

(B) The $R$-factor (Resistance factor) is a type of plasmid found in bacteria that carries genes responsible for resistance to antibiotics or other toxic substances.
It is often referred to as the resistance transfer factor $(RTF)$ because it can be transferred between bacterial cells,typically through the process of conjugation,thereby spreading antibiotic resistance within a population.

(A) Restriction endonucleases are enzymes that cut $DNA$ at specific recognition sequences.
Because of this ability to cut $DNA$ molecules,they are commonly referred to as 'molecular scissors' or 'bioscissors'.
Therefore,the correct option is $A$.

(D) Plasmids are small,circular,double-stranded $DNA$ molecules that are distinct from a cell's chromosomal $DNA$.
They are extranuclear genetic elements found primarily in bacteria.
These plasmids often carry genes that provide advantages to the bacteria,such as antibiotic resistance.
Therefore,the correct option is $D$.

(B) The restriction endonuclease enzyme was discovered by $Hamilton \ Smith$ and $Daniel \ Nathans$ in the early $1970s$.
These enzymes are known as molecular scissors because they cut $DNA$ at specific recognition sequences.
They play a crucial role in genetic engineering and recombinant $DNA$ technology.

(B) Restriction endonucleases are essential tools in genetic engineering,often referred to as 'molecular scissors'.
They recognize specific nucleotide sequences in $DNA$ molecules and cut the $DNA$ at these specific sites.
This property allows scientists to isolate specific genes or $DNA$ fragments to create recombinant $DNA$ molecules,which is the fundamental basis of genetic engineering.

(A) $Ti-$ plasmid (Tumor-inducing plasmid) is naturally found in the soil bacterium $Agrobacterium \text{ } tumefaciens$.
This bacterium is widely used in genetic engineering as a vector to transfer foreign genes into host plants because it can naturally infect plant cells and integrate its $T-DNA$ into the plant genome.

(B) The correct answer is $B$.
$Escherichia coli$ $(E. coli)$ is widely used in genetic engineering as a host organism for cloning and the production of recombinant proteins like insulin (humulin) and growth hormones.
$Agrobacterium tumefaciens$ is a soil bacterium that contains the $Ti$ (Tumor-inducing) plasmid,which is extensively used as a vector for gene transfer in plants.

(D) Restriction endonucleases are enzymes that cut $DNA$ at specific recognition sequences.
Because they act like scissors to cut $DNA$ molecules at precise locations, they are commonly referred to as "molecular scissors" or "biological scissors" in genetic engineering.

(B) Restriction endonucleases are enzymes that recognize specific nucleotide sequences in $DNA$ and cleave both strands of the $DNA$ molecule at or near these recognition sites. They are essential tools in recombinant $DNA$ technology.

(C) Genetic engineering,also known as recombinant $DNA$ technology,involves the manipulation of $DNA$ to create new combinations of genetic material. $A$ $Plasmid$ is a small,circular,extrachromosomal $DNA$ molecule found in bacteria that is widely used as a vector to carry foreign $DNA$ into a host cell. Therefore,it is an essential tool in genetic engineering.

(A) The correct answer is $A$.
$Agrobacterium$ $tumefaciens$ is a soil bacterium that acts as a natural genetic engineer.
It is widely used for gene transfer in higher plants because it possesses a $Ti$ (Tumour inducing) plasmid.
This plasmid can integrate a piece of its own $DNA$,known as $T-DNA$,into the host plant genome,causing the formation of crown gall tumors.
Scientists have modified this $Ti$ plasmid to act as a vector for delivering genes of interest into plant cells.

(B) The enzyme used for the separation or cutting of genetic material $(DNA)$ at specific sites is known as a restriction endonuclease.
These enzymes are often referred to as 'molecular scissors' because they recognize specific nucleotide sequences and cleave the $DNA$ backbone.

(D) Genetic engineering involves the manipulation of the genetic material of an organism using specific enzymes.
Restriction endonucleases are enzymes that cut $DNA$ at specific recognition sequences.
These enzymes were discovered in bacteria,where they serve as a defense mechanism against viral infection.
By purifying these enzymes,scientists can use them in vitro to cut and join $DNA$ fragments,which is the foundation of recombinant $DNA$ technology.
$Nathans$ and $Smith$ $(1970)$ isolated the first restriction endonuclease.
$Jackson$,$Symons$,and $Paul$ $Berg$ $(1972)$ successfully generated recombinant $DNA$ molecules in vitro.

(B) Crown gall disease is a plant disease caused by the soil-borne bacterium $Agrobacterium \text{ tumefaciens}$.
This bacterium transfers a piece of its $DNA$, known as $T-DNA$, into the plant cell, which integrates into the plant genome and causes the formation of tumors or galls.
Therefore, $Agrobacterium$ is the correct answer.

(D) Plasmids are extrachromosomal,covalently closed,circular,double-stranded $DNA$ molecules present in most prokaryotes.
Because of their ability to replicate independently,they are widely used as vectors in genetic engineering to transfer foreign genes into host cells.

(A) Restriction endonucleases are enzymes that cut $DNA$ at specific recognition sequences. They are essential tools in recombinant $DNA$ technology,which is a core component of genetic engineering. These enzymes allow scientists to isolate specific genes and insert them into vectors to create recombinant $DNA$ molecules.

(B) Restriction endonucleases are enzymes that cut $DNA$ at specific recognition sequences.
They are naturally produced by bacteria as a defense mechanism to protect themselves against invading viral $DNA$ (bacteriophages).
For example,the restriction endonuclease $EcoRI$ is produced by the bacterium $Escherichia$ $coli$ strain $RY13$.

(B) Restriction endonucleases are enzymes that recognize specific nucleotide sequences in $DNA$ and cleave the phosphodiester bonds within the double-stranded $DNA$ molecule.
These enzymes act as 'molecular scissors' and are essential tools in genetic engineering for creating recombinant $DNA$ molecules.
They typically cut the $DNA$ double helix at specific recognition sites,often resulting in single-stranded free ends known as 'sticky ends' or sometimes 'blunt ends'.

(D) $pBR 322$ is a well-known engineered plasmid used as a cloning vector in biotechnology.
$Alu I$,$Hind III$,and $Eco RI$ are all restriction endonucleases (enzymes),not plasmids.

(B) The process of synthesizing $DNA$ from an $RNA$ template is known as reverse transcription. The enzyme responsible for this process is reverse transcriptase. $cDNA$ (complementary $DNA$) is synthesized in the laboratory using $mRNA$ as a template and the enzyme reverse transcriptase. Therefore,the correct option is $B$.

(B) recombination vector is a $DNA$ molecule used as a vehicle to artificially carry foreign genetic material into another cell,where it can be replicated and/or expressed.
$Agrobacterium$ $tumefaciens$ is a soil bacterium that naturally transfers a segment of its $DNA$,known as $T$-$DNA$,into the plant genome.
In biotechnology,the Ti plasmid of $Agrobacterium$ $tumefaciens$ is modified to serve as a cloning vector for the delivery of genes of interest into plants.

(A) Crown gall disease in plants is caused by the bacterium $Agrobacterium$ $tumefaciens$.
This bacterium contains a specific plasmid known as the tumour-inducing or $Ti-$ plasmid.
The $Ti-$ plasmid is responsible for transferring a segment of $DNA$, known as $T-DNA$, into the plant genome, which leads to the formation of crown galls (tumours).

(A) $E. coli$ (Escherichia coli) is the most commonly used bacterium in genetic engineering.
It is widely used as a host organism for cloning and expression of recombinant $DNA$ because it has a well-characterized genome,grows rapidly,and is easy to manipulate in the laboratory.
Other options like $Diplococcus$,$Rhizobium$,and $Spirillum$ are not standard model organisms for routine genetic engineering procedures compared to $E. coli$.