Test: Principles of Biotechnology (NCERT) - NEET MCQ

The first recombinant DNA was constructed by Stanley Cohen and Herbert Boyer in 1972. They cut the piece of DNA from a plasmid carrying antibiotic resistance gene in the bacterium Salmonella typhimurium and linked it to the plasmid of Escherichia coil.

NCERT Topic: Plasmid used to construct recombinant DNA

NCERT Line: "DNA emerged from the possibility of linking a gene encoding antibiotic resistance with a native plasmid (autonomously replicating circular extra-chromosomal DNA) of Salmonella typhimurium."

The restriction endonuclease enzyme inspects the length of a DNA sequence. Once it recongnises specific sequence, it binds to the DNA and cuts each of the two strands of the double helix at specific points in their sugar phosphate back bone. Special sequence in the DNA recongnised by restriction endonuclease is called palindromic nucleotide sequence. Restriction endonuclease enzymes are also known as molecular scissors or biological scissors or chemical knives or chemical scalpels.

NCERT Topic: Restriction enzymes

NCERT Line: "Restriction enzymes belong to a larger class of enzymes called nucleases."

After cutting the source DNA and the vector DNA with a specific restriction enzyme, the cut out 'gene of interest' from the source DNA and the cut vector with space are mixed and ligase enzyme is added. This results in the formation of rDNA or hybrid DNA or chimeric DNA.

NCERT Topic: Recombinant DNA technology

NCERT Line: "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°C (heat shock), and then putting them back on ice."

The statement that is not correct is:

3. Log phase does not show any significant increase in the number of cells whereas the lag phase shows rapid multiplication of cells.

Here's why:

• Log phase (or exponential phase) is actually characterized by a rapid and significant increase in the number of cells. During this phase, cells are dividing at an exponential rate.

• Lag phase is the initial phase where cells are adapting to new conditions and preparing for growth. During this phase, there is little to no significant increase in cell number as the cells are not yet dividing rapidly.

To summarize, the log phase is when cell multiplication is most rapid, not the lag phase.

In 1972, genetic engineering was started by Paul Berg. He was able to introduce a gene of the SV-40 virus into a bacterium with the help of lambda phage. Berg is often considered as "Father of genetic engineering". He was awarded Nobel Prize in 1980.

The restriction endonuclease enzyme inspects the length of a DNA sequence. Once it recognises specific sequence, it binds to the DNA and cuts each of the two strands of the double helix at specific points in their sugar phosphate back bone. Special sequence in the DNA recognised by restriction endonuclease is called palindromic nucleotide sequence. Restriction endonuclease enzymes are also known as molecular scissors or biological scissors or chemical knives or chemical scalpels.

NCERT Topic: Restriction enzymes

NCERT Line: "Restriction enzymes belong to a larger class of enzymes called nucleases. These are of two kinds; exonucleases and endonucleases."

Plasmids are extra-chromosomal, self-replicating, usually circular, double-stranded DNA molecules found naturally in many bacteria and also in some yeasts. Plasmids are usually not essential for normal cell growth and division, they often confer some traits to the host organism e.g., resistance to certain antibiotics. The plasmid that is used as a carrier for transferring a fragment of foreign DNA into a suitable host is called vehicle DNA or cloning vector or gene carrier.

NCERT Topic: Plasmid as a vector

NCERT Line: "In the same way, a plasmid can be used as vector to deliver an alien piece of DNA into the host organism."

Genetic engineering is the artificail synthesis, isolation modification, cimbination, addition and repaor of the genetic material (DNA) to alter the phenotype of the host organism to suit human needs. It is the manipulation of genes by man in vitro. Restriction endonucleases play major role in gentic engineering as they can cut DNA at specific sites.

NCERT Topic: Cutting of DNA at specific locations

NCERT Line: "Restriction endonucleases are used in genetic engineering to form 'recombinant' molecules of DNA, which are composed of DNA from different sources/genomes."

Biotechnology deals with techniques of using live micro-organisms, plant or animal cells or their components or enzymes from organisms to produce products and processes (service) useful to human beings. In vitro fertilisation, synthesis of recombinant gene, correcting a defective gene and developing a DNA vaccine are all parts of biotechnology.

NCERT Topic: Processes included under biotechnology

NCERT Line: "Further, many other processes/techniques are also included under biotechnology. For example, in vitro fertilisation leading to a 'test-tube' baby, synthesising a gene and using it, developing a DNA vaccine or correcting a defective gene, are all part of biotechnology."

• The father of genetic engineering is Paul Berg. He creates the recombinant DNA technology in 1972.
• Kary Mullis invents the polymerase chain reaction in 1993. Arber, Smith and Nathan discovered the restriction endonuclease enzymes in 1978.
• Stanley Cohen and Herbert Boyer constructed artificial recombinant DNA for the first time. They got the idea of linking a gene encoding for antibiotic resistance with a native plasmid of Salmonella typhinurium.