Question

The construction of the first recombinant DNA was done by using the native plasmid of
A. Escherichia coli
B. Salmonella typhimurium
C. Bacillus thuringiensis
D. Yeast
E. Agrobacterium

Answer 1

Hint: Recombinant technology allows us to manipulate and duplicate the DNA or genes with desired characteristics. The first artificially constructed recombinant DNA was linked with the gene encoding for the antibiotic resistance in a host organism. The host organism used as E.coli.

Complete answer: Genetic engineering, also known as recombinant technology, also allows the study of genomes and has many applications that can benefit mankind. It also allows gene cloning where a whole new organism can be created from the existing one to maybe preserve their existence or to study an organism. Recombinant technology involved the use of plasmids, molecular scissors, and DNA ligase. Plasmids help in transferring the required DNA from the source to the host cell. Plasmids are self-replicating and show desirable results in the host cell once inserted. Molecular scissors or restriction endonucleases are scissors-like where they can cut at the desired position in a given genome. DNA ligases are the molecules that help in joining the created DNA fragments into one single plasmid and helps in transferring. In 1972, some scientists like Stanley Cohen and Herbert Boyer observed that an organism which shows antibiotic resistance because of a gene and that gene can be transferred to another organism so that they can acquire the resistance. They took the resistance plasmid from Salmonella typhimurium. They isolated the plasmid first. Then, they treated the plasmid with a restriction endonuclease which cut the resistance gene. This was transferred using vectors in the host cell. For E.coli, the vector used is pBR322. DNA ligase is used to join the fragments into a vector.
This newly formed circular recombinant DNA was transferred to E.coli. This was replicated in the host cell and the transformed cells were isolated using the marker on the transferred gene.
Thus, the correct answer is option B-Salmonella typhimurium.

Note: Though the most used organism in the recombinant technology is E.coli, the bacterial plasmid of S.typhimurium was used as it contained the antibiotic resistance. Agrobacterium is a gram negative bacterium which is also used in genetic transfer in plants.