Tools of recombinant DNA technology Questions in English

(D) The correct answer is $D$.
Restriction enzymes are named based on the genus and species of the bacterium from which they are isolated.
The first letter of the genus is written in capital letters,followed by the first two letters of the species name.
For $Sal I$,'$S$' comes from the genus $Streptomyces$ and '$al$' comes from the species $albus$.
Therefore,$Sal I$ is isolated from $Streptomyces albus$.

(A) The correct answer is $A$.
Restriction endonucleases are enzymes produced by bacteria as a defense mechanism against bacteriophages (viruses that infect bacteria).
These enzymes recognize specific $DNA$ sequences and cleave the viral $DNA$,thereby preventing the infection and replication of the virus within the bacterial cell.

(D) The correct answer is $D$.
Plasmids are small,circular,double-stranded $DNA$ molecules that are distinct from a cell's chromosomal $DNA$.
They are found primarily in bacteria and are much smaller in size compared to the chromosomal $DNA$ of the host cell.
Therefore,the statement that plasmid $DNA$ is as long as chromosomal $DNA$ is incorrect.

(A) The correct answer is $A$.
Biolistics,also known as the gene gun method,is the most suitable technique for introducing foreign $DNA$ into plant cells.
In this method,cells are bombarded with high-velocity micro-particles of gold or tungsten coated with $DNA$.
Microinjection is typically used for animal cells,lipofection is used for animal cells,and the heat shock method is primarily used for bacterial transformation.

(A) Plasmid.
Plasmids are extra-chromosomal,self-replicating,circular,$dsDNA$ molecules.
Plasmid vectors are typically used to clone small $DNA$ fragments,usually ranging from $100$ to $1000$ $bp$.

(A) palindromic $DNA$ sequence is a sequence of base pairs that reads the same when the orientation of reading is the same,i.e.,$5'$ to $3'$ on both strands.
Let's analyze the options:
$A$: $5'-GGATCC-3'$ and $3'-GGTACC-5'$. The complementary strand of $5'-GGATCC-3'$ is $3'-CCTAGG-5'$. Since $3'-GGTACC-5'$ does not match $3'-CCTAGG-5'$,this is not a palindrome.
$B$: $5'-GAATTC-3'$ and $3'-CTTAAG-5'$. This is a palindrome (EcoRI site).
$C$: $5'-GCGGCCGC-3'$ and $3'-CGCCGGCG-5'$. This is a palindrome (NotI site).
$D$: $5'-CCCGGG-3'$ and $3'-GGGCCC-5'$. This is a palindrome (SmaI site).
Therefore,option $A$ is the correct answer.

(C) The desirable characteristics for a cloning vector (plasmid) are:
$1$. Origin of replication $(ori)$: $A$ site at which replication can be initiated $(C)$.
$2$. Selectable markers: One or more identifiable marker genes $(D)$ to identify and eliminate non-transformants.
$3$. Cloning sites: One or more unique restriction sites $(E)$ for the insertion of foreign $DNA$.
Therefore,the correct characteristics are $C, D,$ and $E$. Option $A$ is incorrect because plasmids must replicate inside the host cell. Option $B$ is a feature of expression vectors,not necessarily cloning vectors.

(B) $EcoRI$ is a restriction endonuclease enzyme that cuts $DNA$ between $G$ and $A$ in the base sequence $5'-GAATTC-3'$.

(B) $EcoRI$ is a restriction enzyme isolated from the bacterium $Escherichia$ $coli$. It cuts $DNA$ at the palindromic sequence $5'-GAATTC-3'$,specifically between the $G$ and $A$ on each strand. This staggered cleavage produces single-stranded overhangs known as sticky ends,which facilitate the joining of $DNA$ fragments.

(C) restriction endonucleases and ligases.
The enzymes absolutely necessary for recombinant $DNA$ technology are restriction endonucleases and ligases.
$1$. Restriction endonucleases act as molecular scissors that cut $DNA$ at specific recognition sequences.
$2$. Ligases act as molecular glue that joins $DNA$ fragments together to form recombinant $DNA$ molecules.
$3$. Topoisomerases are involved in relieving $DNA$ supercoiling but are not the primary tools for recombination.
$4$. Polymerases are used for $DNA$ amplification $(PCR)$ but are distinct from the cutting and joining enzymes required for basic recombinant construction.
$5$. Peptidases are enzymes that break down proteins and have no role in $DNA$ manipulation.

(D) The convention for naming restriction enzymes involves using the first letter of the genus and the first two letters of the species of the prokaryotic cell.
Thus,$Bacillus$ $amyloliquefaciens$ gives '$Bam$'.
The strain is indicated by the following letter ('$H$'),and the Roman numeral indicates the order of discovery.
Therefore,it is named $Bam$ $HI$.

(D) In the $PCR$ (Polymerase Chain Reaction) method,$Taq$ polymerase is the heat-stable $DNA$ polymerase enzyme used in the extension phase to synthesize $DNA$ strands. It is derived from the bacterium $Thermus$ $aquaticus$ and can withstand the high temperatures required for denaturing $DNA$.

(A) Statement $A$ is true: Restriction endonucleases are known as molecular scissors.
Statement $B$ is true: They were discovered in $E. coli$ as a mechanism to restrict bacteriophage growth.
Statement $C$ is false: Restriction enzymes do not always cut at the exact center of palindromic sites; they often create staggered cuts.
Statement $D$ is false: Restriction endonucleases cut $DNA$ at specific internal positions,whereas exonucleases remove nucleotides from the ends.
Statement $E$ is true: They recognize specific palindromic sequences.
Therefore,statements $C$ and $D$ are not true.

(C) The cloning vector $pBR322$ contains two antibiotic resistance genes: one for ampicillin $(amp^R)$ and one for tetracycline $(tet^R)$.
In $pBR322$,the $BamHI$ restriction site is specifically located within the tetracycline resistance $(tet^R)$ gene.
When a foreign $DNA$ fragment is inserted at the $BamHI$ site,it disrupts the coding sequence of the $tet^R$ gene.
As a result,the bacteria containing this recombinant plasmid lose their ability to survive in the presence of tetracycline,a phenomenon known as insertional inactivation.