Biotechnology in medicines:

• The recombinant DNA technology is used in the production of therapeutic drugs and these drugs are safe and more effective.
• It avoids unwanted immunological responses common in case of similar products isolated from non-human sources.

Genetically engineered insulin:

• Insulin consists of two short polypeptide chains: chain A and chain B, that are linked together by
  di-sulphide bridges.
•  In mammals, including humans, insulin is synthesized as a pro-hormone (like a pro-enzyme, the pro-hormone also needs to be processed before it becomes a fully mature and functional hormone) which contains an extra stretch called the C peptide.
• This C peptide is not present in the mature insulin and is removed during maturation into insulin. Earlier, insulin was extracted from pancreas of cattle and pigs but these found to be allergic.
• In 1983, Eli Lilly an American company prepared two DNA sequences corresponding to A and B, chains of human insulin and introduced them in plasmids of E. coli to produce insulin chains. Chains A and B were produced separately, extracted and combined by creating disulfide bonds
  to form human insulin.

Gene therapy:

• Gene therapy is a collection of methods that allows correction of a gene defect that has been diagnosed in a child/embryo.
• Correction of a genetic defect involves delivery of a normal gene into the individual or embryo to take over the function of and compensate for the non-functional gene.
• The first clinical gene therapy was given to a 4-year old girl who was suffering from adenosine de-aminase (ADA) deficiency. This enzyme is crucial for the immune system to function and caused by the deletion of the gene for adenosine de-aminase.
• In some cases ADA deficiency can be cured by bone marrow transplantation or enzyme replacement therapy but the problem with both of these approaches that they are not completely curative.
• In much better cure of this deficiency, lymphocytes from the blood of the patient are grown in a culture plate.
• A functional ADA cDNA (using a retroviral vector) is then introduced into these lymphocytes, which are subsequently returned to the patient. But these cells are not immortal so the patient requires periodic infusion of such genetically engineered lymphocytes.
• If gene isolated from marrow cells producing ADA is introduced into cells at early embryonic stages, it could be a permanent cure.

Molecular diagnosis:

Some techniques for early diagnosis of disease:

1. Recombinant DNA technology:

• Very low concentration of a bacteria or virus can be detected by amplification of their nucleic acid by PCR.
•  PCR is now routinely used to detect HIV in suspected AIDS patients.
•  It is being used to detect mutations in genes in suspected cancer patients too.  
• It is a powerful technique to identify many other genetic disorders.

2. Polymerase Chain Reaction (PCR):

• A single stranded DNA or RNA, tagged with a radioactive molecule is called probe.
•  A probe is allowed to hybridize to its complementary DNA in a clone of cells.
• Then they get detected by using autoradiography.
• The clone having the mutated gene will hence not appear on the photographic film, because the probe has no complementary sequence with the mutated gene.

3. Enzyme Linked Immuno-sorbent Assay (ELISA):

• ELISA is based on the principle of antigen-antibody interaction.
• Infection by pathogen can be detected by the presence of antigens (proteins, glycol-proteins, etc.) or by detecting the antibodies synthesized against the pathogen.