MCQ 23 Dec 2023

Daily practice questions for CLAT - (23 December 2023)

Can gene therapy substitute for surgery to remove a brain tumour? Clinical trials, involving 15 patients at the National Institute of Health in Bethesda, US point to a positive answer. A team led by Michael Blaese claims concrete proof of gene therapy being a practical approach to tackle cancer. Blaese, chief of the Clinical Gener Therapy Branch of the National Centre for Human Genome Research at the NIH, has used ‘suicide genes’ from the herpes simplex virus riding into brain tumour cells on retroviruses have RNA and DNA as their genetic material, but need an intermediate DNA for replication. The first trial was encouraging enough for us to continue with a large trial that addresses itself to patients suffering from high-grade brain cancer, people who do not have more than six months to live. His technique is based on exploiting a characteristic feature of the retroviruses – that they can transfer genes only into actively dividing cells. A cancerous cell or tumour divides prolifically whereas healthy brain cells do not divide at all. This means the retrovirus carrying the herpes simplex gene will enter only the abnormal brain cells. As the brain is more immunologically privileged than those other parts of the body, it allows these incompatible cells from the mouse to persist without any rejection or reaction. Once the HS-tk gene gets into the cancer cells of the tumour, it makes those cells behave just like virus cells. Blaese says, “We have used HS-tk in order to change the metabolism of the tumour cell so that it would mimic the cell of a virus. Then we can treat the tumour cell with an anti-viral drug.” After being treated with a retrovirus, patients are put on Ganciclovir. Ganciclovir, a common anti-herpes drug, kills the cancerous cells which appear like viral cells thanks to the HS-tk gene in them. This function of the HS-tk has earned it the name of a ‘suicide gene’. Though the suicide genes are not put into each cancerous cell in the procedure, tumour regression is almost complete after gene therapy. This, according to Blaese, is the result of the ‘bystander effect’ that is, the poison produced by the gene can spread to adjacent cells of the tumour through gap junctions. The first phase of the clinical trials was designed to test the efficiency of the method and to probe its possible toxic effects. From the target group of 15 patients, one survived for 25 months, increasing the expected life span of 19 months! I do not want to mislead people by saying this is the magic bullet that is going to cure brain cancer, but I do not hope this will be another tool that is effective in cancer treatment. What if the virus spreads to non-tumour tissues within or outside the central nervous system? What if the viral cells proliferate right where they are injected? And there is the possibility of the interaction between the Hs-tk and Ganciclovir this generating toxic by-products that might damage even healthy cells.

Question1:- What, according to the passage is the distinguishing trait of retrovirus?
  • (a) The presence of RNA in them.
  • (b) They act as vehicles to control and contain the growth of brain cancer.
  • (c) They can transfer genes only to actively dividing cells.
  • (d) They are easy targets for suicide genes.
Answer is C is correct. This is a fact-based question. The author has mentioned that the retroviruses have special characteristics of transferring genes to the actively dividing cells. Hence, option (c) is the correct answer. The presence of RNA is relevant for them. But it is not a distinguishing feature. So, option (a) is not the answer. Option (b) and (d) are not supported by the passage. Hence, option (c) is the correct answer.
Question2:- Which of the following is not an apprehension expressed in the passage regarding the effectiveness of gene therapy?
  • (a) The spreading of the virus to non-tumour tissues within or outside the central nervous system.
  • (b) Proliferation of the viral cells right where they are injected.
  • (c) Generation of toxic by-products as a result of interaction between HS-tk and Ganciclovir.
  • (d) The therapy is expensive and not effective for public use as the sample size is small.
Answer is D is correct. The therapy is effective and shows bright results but with some apprehensions. The apprehensions mentioned in the passage are – the effect of the suicide virus on the nervous system (Option a), the proliferation of cells (Option b) and the generation of harmful chemicals due to the mixing of viruses with the drugs. (Option c). But the option (d) seems not related to the passage. The author has not talked about the cost of the therapy and its application to the general public. Hence, option (d) is the correct answer.
Question3:- What is a conclusion based on the passage?
  • (a) The author is not so confident of the success of the therapy.
  • (b) The gene therapy can be successfully used for treating brain tumours.
  • (c) A large trial can only establish the utility of the therapy.
  • (d) The gene therapy has so many side effects that it is not useful.
Answer is A is correct. The passage does not conclude that gene therapy’s success in the gene therapy. It only says that results are encouraging. The author has expressed his reservations about the success of the theory in treating cancer right now. He says that it might be an effective tool in the future only. Option (a) is a conclusion based on the passage. Option (c) and (d) are fictitious and not based on the facts given in the passage. Side effects and trials are not discussed in relation to the failure or rejection of the theory. Hence, option (a) is the correct answer.
Question4:- What can be inferred about the ‘suicide gene’?
  • (a) It generates substances that kill it.
  • (b) They can change the identity of cancer cells into viral cells.
  • (c) Divides the viral cells without any hindrance.
  • (d) Attacks the tumour cells to destroy them at their own cost.
Answer is B is correct. Solution: HS- tk is called the suicide gene by the author. Suicide genes perform a specialised function to change the identity of the tumour cells and convert them into viral cells that can be treated by drugs. This function of the HS-tk has earned it the name of a ‘suicide gene’. Option (b) is the correct answer.
Question5:- What does the author imply by the term ‘bystander effect?
  • (a) Permeation of the poison produced by the suicide gene to adjacent cells.
  • (b) Impassive participation of genes in the growth of tumours in gap junctions.
  • (c) The gene gets killed in the process.
  • (d) The genetic modification of cancer cells.
Answer is A is correct. The suicide gene, HS-tk, is not applied to the target tumour cells directly. So, it can affect the adjacent areas. The poison produced by the gene can spread to adjacent cells of the tumour through gap junctions. So, the bystanders, though not genetically modified, can still be killed in the process. This is the bystander effect. Option (a) is the correct answer.