Read the passage and answer the following questions:
In almost all recombinant technologies, the ultimate aim is to produce a desirable protein. Hence, there is a need for the recombinant DNA to be expressed. The foreign gene gets expressed under appropriate conditions. After having cloned the gene of interest and having optimised the conditions to induce the expression of the target protein, one has to consider producing it on a large scale. The cells harbouring cloned genes of interest may be grown on a small scale in the laboratory. The cultures may be used for extracting the desired protein and then purifying it by using different separation techniques. Small volume cultures cannot yield appreciable quantities of products. To produce in large quantities, the development of bioreactors, where large volumes of culture can be processed, was required. The most commonly used bioreactors are of stirring type.
A laboratory has cloned a gene of interest in bacterial cells and optimised the conditions for the expression of the protein. The cells are grown in a few small culture flasks, but the protein extracted from them is far too little for commercial use. Which of the following steps should be taken next?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Grow the cells on a large scale in a bioreactor
The gene is already cloned and its expression is already optimised. What is missing is quantity. The passage states that small volume cultures cannot yield appreciable quantities of products, and that bioreactors were developed so that large volumes of culture can be processed.
Option (1) Amplify the gene of interest many times using PCR — Incorrect. PCR makes more copies of the gene in a tube. It does not raise the amount of protein that a few small flasks of cells can make.
Option (2) Grow the cells on a large scale in a bioreactor — Correct. Large volumes of culture give large quantities of the protein, which is what commercial use needs.
Option (3) Send the extracted protein for downstream processing — Incorrect. Downstream processing separates and purifies the product. It does not increase the amount made, and here the amount itself is too small.
Option (4) Transfer the recombinant DNA again into fresh competent cells — Incorrect. The cells already carry the cloned gene and express it. Transforming fresh cells still leaves a small culture.