Read the passage carefully to answer the questions given below.
Some strains of Bacillus thuringiensis produce proteins that kill certain insects such as lepidopterans (tobacco budworm, armyworm), coleopterans (beetles) and dipterans (flies, mosquitoes). In Bacillus thuringiensis the toxin is coded by a gene cryIAc named cry. There are a number of them, for example, the proteins encoded by the genes cryIAc and cryIIAb control the cotton bollworms, that of cryIAb controls corn borer. Using conventional methods of diagnosis (serum and urine analysis, etc.) early detection is not possible. Recombinant DNA technology, Polymerase Chain Reaction (PCR) and Enzyme Linked Immuno-sorbent Assay (ELISA) are some of the techniques that serve the purpose of early diagnosis. The first clinical gene therapy was given in 1990 to a 4-year old girl with adenosine deaminase (ADA) deficiency. This enzyme is crucial for the immune system to function. The disorder is caused due to the deletion of the gene for adenosine deaminase. RNAi takes place in all eukaryotic organisms as a method of cellular defense. This method involves silencing of a specific mRNA due to a complementary dsRNA molecule that binds to and prevents translation of the mRNA.
The first clinical gene therapy was given in 1990 to a 4-year old girl with adenosine deaminase (ADA) deficiency. This disorder is caused due to the deletion of the gene for -
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Adenosine deaminase
ADA deficiency is caused by the deletion of the gene for the enzyme adenosine deaminase. This enzyme is needed for the immune system to work, so the child cannot fight infections. In the first gene therapy (1990), a working ADA gene was put into the girl’s lymphocytes.
Option (1) Adenosine decarboxylase — Incorrect. ‘ADA’ stands for adenosine deaminase, an enzyme that removes an amino group, not a carboxyl group.
Option (2) Adenosine dehydrogenase — Incorrect. A dehydrogenase removes hydrogen; it is not the enzyme missing in ADA deficiency.
Option (3) Adenosine deaminase — Correct. ADA deficiency is caused by the deletion of the gene for the enzyme adenosine deaminase, which is needed for the immune system to work. The disorder is named after this missing enzyme.
Option (4) Adenosine deacetylase — Incorrect. A deacetylase removes an acetyl group; it does not expand ‘ADA’.
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.