BIOTECHNOLOGY : PRINCIPLES AND PROCESSES
Read the following passage carefully and answer the given questions.
Biotechnology deals with large scale production and marketing of products and processes using live organisms, cells or enzymes. Modern biotechnology using genetically modified organisms was made possible only when man learnt to alter the chemistry of DNA and construct recombinant DNA. This key process is called recombinant DNA technology or genetic engineering. This process involves the use of enzymes, viral vectors to carry the foreign DNA into host organisms, expression of the foreign gene, purification of the gene product, and finally making a suitable formulation for marketing. Restriction endonucleases are used in genetic engineering to form ‘recombinant’ molecules of DNA, which are composed of DNA from different sources/genomes. Gene cloning allows us to isolate and introduce only one or a set of desirable genes without introducing undesirable genes into the target organism. The ability to multiply copies of antibiotic resistance gene in E. coli was called cloning of antibiotic resistance gene in E. coli. In PCR, multiple copies of the gene (or DNA) of interest is synthesised in vitro using two sets of primers (small chemically synthesised oligonucleotides that are complementary to the regions of DNA) and the enzyme DNA polymerase.
Which one of the followings is not a step involved in the process of polymerase chain reaction (PCR)?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Transcription
The polymerase chain reaction (PCR) makes many copies of a piece of DNA in a test tube. It uses two sets of primers and the enzyme DNA polymerase. Each cycle has three steps, and the cycle is repeated many times.
(1) Extension — A step of PCR. The enzyme extends the primers using the nucleotides in the reaction. The genomic DNA is the template.
(2) Denaturation — A step of PCR. The double-stranded DNA is heated, so that the two strands separate.
(3) Transcription — Not a step of PCR. Transcription is the making of RNA from DNA inside a cell. No RNA is made in PCR.
(4) Primer annealing — A step of PCR. The two primers bind to the matching regions of the separated strands.
Note: The passage is taken from NCERT. NTA has put lines of the NCERT text together to make it. Most CUET (UG) questions come straight from NCERT, so study the book line by line, including figures and their titles.