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Question

(a) What is plasmid ?
(b) What is meant by ADA deficiency?
(c) How is gene therapy a solution to this problem?
(d) Why is it not a permanent cure ?

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Solution

  1. Plasmid are the extra chromosomal small circular DNA molecules in addition to the chromosomal DNA. Plasmid capable of replicating independently of the chromosomal DNA. In some cases plasmid are circular and double stranded. plasmids usually occur naturally inn bacteria.
  2. Adenosine deaminase deficiency (also called ADA deficiency or ADA-SCID) is an autosomal recessive metabolic disorder that causes immuno-deficiency. ADA deficiency is due to a lack of the enzyme adenosine deaminase. This deficiency results in an accumulation of deoxyadenosine which, in turn, leads to buildup of the ATP in all cells, which inhibits ribonucleotide reductase and prevents DNA synthesis, so cells are unable to divide.
  3. This is often treated through gene therapy. Lymphocytes from the blood of patients are grown in-culture medium outside the body. A functional ADA DNA is then introduced to this lymphocytes, which are subsequently return to patients. How ever, as these cells are not immortal, patient require periodic infusion of such genetically engineered lymphocytes.



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