How Bacteria Became Factories for Human Insulin
See how human insulin is produced by genetic engineering, how gene therapy treats ADA deficiency, how PCR, ELISA and probes diagnose disease early, and why transgenic animals, GEAC regulation, biopiracy and patents matter.
How has biotechnology changed medicine?
Biotechnology has given doctors safer medicines, new ways to fix faulty genes, tests that catch diseases early, and animals that help study illness — while raising hard questions about safety, fairness and who owns nature's resources.
This part covers genetically engineered insulin, gene therapy, molecular diagnosis, and transgenic animals with the ethical issues around them.
This part covers genetically engineered insulin, gene therapy, molecular diagnosis, and transgenic animals with the ethical issues around them.
How is human insulin made by genetic engineering, and how was the problem of joining its chains solved?
Human insulin has two short polypeptide chains, A and B, linked by disulphide bridges; because the natural precursor, pro-insulin, carries an extra C-peptide that must be removed, DNA sequences for chains A and B were made separately, expressed in E. coli, and the purified chains were then joined by forming disulphide bonds.
Structure of insulin:
- Two polypeptide chains, A and B, linked by disulphide bridges
- In mammals it is made as pro-insulin, which contains an extra stretch, the C-peptide
- The C-peptide is removed during maturation into insulin
Why earlier insulin was a problem. Insulin extracted from the pancreas of slaughtered cattle and pigs caused allergies and other reactions in some patients.
The genetic engineering solution:
- Two DNA sequences corresponding to chains A and B were prepared
- Each was introduced into plasmids of E. coli, which produced the chains separately
- The chains were extracted and combined by creating disulphide bonds, giving human insulin
An everyday example. Insulin pens used by people with diabetes in India contain recombinant human insulin made by microbes.
The substance. Making chains A and B separately avoids the C-peptide problem — the challenge was assembling insulin into its mature form.
Structure of insulin:
- Two polypeptide chains, A and B, linked by disulphide bridges
- In mammals it is made as pro-insulin, which contains an extra stretch, the C-peptide
- The C-peptide is removed during maturation into insulin
Why earlier insulin was a problem. Insulin extracted from the pancreas of slaughtered cattle and pigs caused allergies and other reactions in some patients.
The genetic engineering solution:
- Two DNA sequences corresponding to chains A and B were prepared
- Each was introduced into plasmids of E. coli, which produced the chains separately
- The chains were extracted and combined by creating disulphide bonds, giving human insulin
An everyday example. Insulin pens used by people with diabetes in India contain recombinant human insulin made by microbes.
The substance. Making chains A and B separately avoids the C-peptide problem — the challenge was assembling insulin into its mature form.
How does gene therapy treat adenosine deaminase deficiency, and how does it compare with other treatments?
Gene therapy corrects a genetic defect by delivering a working gene into cells; for adenosine deaminase deficiency, lymphocytes from the patient's blood receive a functional ADA gene through a retroviral vector and are returned to the body, but because these cells do not live forever the treatment must be repeated — while enzyme replacement and bone marrow transplantation are not fully curative either.
ADA deficiency:
- Adenosine deaminase is an enzyme crucial for the immune system
- The disorder is caused by deletion of the ADA gene, leading to severe immunodeficiency
Alternative treatments:
- Bone marrow transplantation
- Enzyme replacement therapy — injecting functional ADA
- Neither is completely curative
Gene therapy:
- Lymphocytes from the patient's blood are grown in culture
- A functional ADA cDNA is introduced into them using a retroviral vector
- The engineered cells are returned to the patient
- Because these cells are not immortal, the patient needs periodic infusions
Towards a permanent cure. Introducing the ADA gene into cells at early embryonic stages could provide a permanent cure.
An everyday example. Replacing a faulty part in a machine rather than repeatedly topping up its fuel — gene therapy tackles the cause, while enzyme replacement only supplies the missing product.
The substance. Gene therapy in lymphocytes is not a one-time cure, because the engineered cells die and must be replaced.
ADA deficiency:
- Adenosine deaminase is an enzyme crucial for the immune system
- The disorder is caused by deletion of the ADA gene, leading to severe immunodeficiency
Alternative treatments:
- Bone marrow transplantation
- Enzyme replacement therapy — injecting functional ADA
- Neither is completely curative
Gene therapy:
- Lymphocytes from the patient's blood are grown in culture
- A functional ADA cDNA is introduced into them using a retroviral vector
- The engineered cells are returned to the patient
- Because these cells are not immortal, the patient needs periodic infusions
Towards a permanent cure. Introducing the ADA gene into cells at early embryonic stages could provide a permanent cure.
An everyday example. Replacing a faulty part in a machine rather than repeatedly topping up its fuel — gene therapy tackles the cause, while enzyme replacement only supplies the missing product.
The substance. Gene therapy in lymphocytes is not a one-time cure, because the engineered cells die and must be replaced.
How do PCR, ELISA and nucleic acid probes help diagnose diseases early?
PCR detects a pathogen by amplifying tiny amounts of its nucleic acid before symptoms appear, a radioactively labelled single-stranded DNA or RNA probe reveals mutated genes by failing to hybridise with them, and ELISA detects antigens or antibodies through antigen–antibody binding.
Why conventional methods fall short. Serum and urine analysis usually detect a disease only after the pathogen has multiplied enough to cause symptoms.
PCR:
- Amplifies very low concentrations of a pathogen's nucleic acid
- Detects HIV in suspected AIDS patients and mutations in genes of suspected cancer patients
Probe hybridisation:
- A single-stranded DNA or RNA tagged with a radioactive molecule hybridises with its complementary DNA in a clone of cells
- The result is detected by autoradiography
- A clone carrying a mutated gene does not appear on the film, because the probe cannot pair with it
ELISA:
- Based on antigen–antibody interaction
- Detects infection through antigens of the pathogen, such as proteins or glycoproteins, or through antibodies made against it
An everyday example. HIV screening at testing centres commonly begins with an ELISA blood test.
The substance. In probe hybridisation, a missing signal is the result — the mutated gene is the one that fails to show up.
Why conventional methods fall short. Serum and urine analysis usually detect a disease only after the pathogen has multiplied enough to cause symptoms.
PCR:
- Amplifies very low concentrations of a pathogen's nucleic acid
- Detects HIV in suspected AIDS patients and mutations in genes of suspected cancer patients
Probe hybridisation:
- A single-stranded DNA or RNA tagged with a radioactive molecule hybridises with its complementary DNA in a clone of cells
- The result is detected by autoradiography
- A clone carrying a mutated gene does not appear on the film, because the probe cannot pair with it
ELISA:
- Based on antigen–antibody interaction
- Detects infection through antigens of the pathogen, such as proteins or glycoproteins, or through antibodies made against it
An everyday example. HIV screening at testing centres commonly begins with an ELISA blood test.
The substance. In probe hybridisation, a missing signal is the result — the mutated gene is the one that fails to show up.
Why are transgenic animals produced, and what ethical issues do GEAC, biopiracy and patents raise?
Transgenic animals, which carry manipulated foreign genes, are used to study normal physiology and disease, to produce biological products, and to test the safety of vaccines and chemicals, while India's GEAC regulates GM research and releases, and biopiracy and patents on traditional resources such as Basmati rice, turmeric and neem raise questions of fairness.
Purposes of transgenic animals:
- Normal physiology and development — how genes regulate body functions, such as growth factors
- Study of disease — models for human diseases such as cancer, cystic fibrosis, rheumatoid arthritis and Alzheimer's
- Biological products — the transgenic cow Rosie produced milk containing human alpha-lactalbumin, nutritionally more balanced for human babies
- Vaccine safety — for example, testing polio vaccine on transgenic mice
- Chemical safety — animals made more sensitive to toxic substances give faster results
Ethical issues:
- GEAC, the Genetic Engineering Approval Committee, judges the validity of GM research and the safety of releasing GM organisms
- Biopiracy — the use of bio-resources by companies without proper authorisation from, or compensation to, the countries and people concerned
- Patents have been sought on products and processes based on India's traditional resources, including Basmati rice, turmeric and neem
- Many nations are framing laws to prevent unauthorised exploitation and ensure fair benefit sharing
An everyday example. Turmeric, long used in Indian homes as a wound remedy, became the subject of a patent dispute — showing why traditional knowledge needs legal protection.
The substance. Biopiracy is about permission and payment, not the science — using bio-resources is fair only with consent and shared benefits.
Purposes of transgenic animals:
- Normal physiology and development — how genes regulate body functions, such as growth factors
- Study of disease — models for human diseases such as cancer, cystic fibrosis, rheumatoid arthritis and Alzheimer's
- Biological products — the transgenic cow Rosie produced milk containing human alpha-lactalbumin, nutritionally more balanced for human babies
- Vaccine safety — for example, testing polio vaccine on transgenic mice
- Chemical safety — animals made more sensitive to toxic substances give faster results
Ethical issues:
- GEAC, the Genetic Engineering Approval Committee, judges the validity of GM research and the safety of releasing GM organisms
- Biopiracy — the use of bio-resources by companies without proper authorisation from, or compensation to, the countries and people concerned
- Patents have been sought on products and processes based on India's traditional resources, including Basmati rice, turmeric and neem
- Many nations are framing laws to prevent unauthorised exploitation and ensure fair benefit sharing
An everyday example. Turmeric, long used in Indian homes as a wound remedy, became the subject of a patent dispute — showing why traditional knowledge needs legal protection.
The substance. Biopiracy is about permission and payment, not the science — using bio-resources is fair only with consent and shared benefits.
Exam tip
What earns full marks on medical applications of biotechnology?
For each application, state the problem, the biotechnology solution and its limitation — for example, repeated infusions in ADA gene therapy.
- Insulin: chains A and B made separately in E. coli and joined by disulphide bonds
- Gene therapy: ADA cDNA placed in lymphocytes with a retroviral vector; not permanent
- Diagnosis: PCR for tiny pathogen amounts, radioactive probes with autoradiography, ELISA
- Ethics: GEAC, biopiracy, patents on Basmati, turmeric and neem
The trap. Calling lymphocyte-based ADA gene therapy a permanent cure. The engineered cells die, so infusions must be repeated.
- Insulin: chains A and B made separately in E. coli and joined by disulphide bonds
- Gene therapy: ADA cDNA placed in lymphocytes with a retroviral vector; not permanent
- Diagnosis: PCR for tiny pathogen amounts, radioactive probes with autoradiography, ELISA
- Ethics: GEAC, biopiracy, patents on Basmati, turmeric and neem
The trap. Calling lymphocyte-based ADA gene therapy a permanent cure. The engineered cells die, so infusions must be repeated.
Did you know
What is a knockout mouse, and why is it so useful?
Scientists can create mice in which one chosen gene has been switched off. These are called knockout mice.
By comparing them with normal mice, researchers see exactly what that gene does — for instance, whether losing it causes obesity, a weak immune system or a condition resembling a human disease.
Because mice share many genes with humans, knockout mice have become powerful tools for understanding human illness and testing possible treatments.
By comparing them with normal mice, researchers see exactly what that gene does — for instance, whether losing it causes obesity, a weak immune system or a condition resembling a human disease.
Because mice share many genes with humans, knockout mice have become powerful tools for understanding human illness and testing possible treatments.
Exam relevance
How are insulin, gene therapy and transgenic animals tested in NEET?
Medical applications of biotechnology complete Biotechnology and its Applications, a recurring NEET Biology chapter.
What gets asked. Why chains A and B were made separately and the role of the C-peptide, the steps and limitation of ADA gene therapy, which technique suits early diagnosis, and uses of transgenic animals such as Rosie.
Question types. Statement-based and assertion-reason questions, and match-the-column questions pairing techniques or products with their uses.
The trap that costs marks. Thinking the C-peptide is part of mature insulin — it is removed from pro-insulin.
What gets asked. Why chains A and B were made separately and the role of the C-peptide, the steps and limitation of ADA gene therapy, which technique suits early diagnosis, and uses of transgenic animals such as Rosie.
Question types. Statement-based and assertion-reason questions, and match-the-column questions pairing techniques or products with their uses.
The trap that costs marks. Thinking the C-peptide is part of mature insulin — it is removed from pro-insulin.
Key takeaways
What must you be able to do from this part?
- Insulin: chains A and B produced separately in E. coli and joined by disulphide bonds, avoiding the C-peptide of pro-insulin
- Gene therapy: a functional ADA gene placed in lymphocytes with a retroviral vector; repeated infusions are needed
- Early diagnosis: PCR, radioactive probes with autoradiography, and ELISA
- Transgenic animals and ethics: disease models, alpha-lactalbumin in milk, vaccine and chemical testing; GEAC, biopiracy and patents
Why must lymphocyte-based ADA gene therapy be repeated, and what could make it permanent?
- Gene therapy: a functional ADA gene placed in lymphocytes with a retroviral vector; repeated infusions are needed
- Early diagnosis: PCR, radioactive probes with autoradiography, and ELISA
- Transgenic animals and ethics: disease models, alpha-lactalbumin in milk, vaccine and chemical testing; GEAC, biopiracy and patents
Why must lymphocyte-based ADA gene therapy be repeated, and what could make it permanent?