Q.The polypeptide chain-A and chain-B of insulin are joined to each other by which bond?
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🔒 Start your 14-day free trial to unlock the full solution →Concept understanding — Recombinant Protein Therapeutics
Imagine you need a specific medicine—say, insulin for diabetes—but the only way to get it used to be from the pancreas of cows or pigs. That was expensive, risky (animal proteins could trigger allergies), and never quite identical to human insulin. Now, we can take the human gene that makes insulin, put it into a harmless bacterium or yeast, and let that microbe churn out perfect human insulin in huge vats. That is the core idea of recombinant protein therapeutics.
Recombinant means "made by combining DNA from different sources." Protein therapeutics means "a protein used as a medicine." So, recombinant protein therapeutics are medicines that are proteins, made by genetically engineered living cells, to treat or prevent disease.
The NCERT textbook (Class 12 Biology, Chapter 12, Biotechnology and its Applications) introduces this under "Biotechnological Applications in Medicine." It specifically mentions human insulin (Humulin) as the first recombinant therapeutic approved for human use. The textbook explains that the human insulin gene was inserted into E. coli bacteria, which then produced insulin identical to our own.
How does it work, step by step?
- Identify the gene that codes for the therapeutic protein (e.g., the gene for human insulin, growth hormone, or clotting factor).
- Insert that gene into a "vector" (a carrier DNA, often a plasmid from a bacterium) using restriction enzymes and DNA ligase.
- Introduce the vector into a host cell (usually E. coli bacteria, yeast, or mammalian cells). This host cell is now "transformed" – it carries the human gene.
- Grow the host cells in large fermenters. As they multiply, they follow the human gene's instructions and produce the human protein.
- Purify the protein from the culture. The final product is a pure, human-identical therapeutic protein, free from animal contaminants.
Why does this matter? (The "why" for a commerce/humanities student)
- Safety and Efficacy: Because the protein is exactly human, the body rarely rejects it. No risk of animal viruses or allergic reactions to animal proteins.
- Scalability: You can produce massive quantities in a lab, independent of animal supply. One batch of engineered bacteria can make more insulin in a day than thousands of pig pancreases.
- Cost (eventually): While initial R&D is expensive, mass production drives down cost, making life-saving drugs accessible to more people.
- New Treatments: It enables therapies that were impossible before—like monoclonal antibodies for cancer, or erythropoietin for anaemia in kidney patients.
The NCERT textbook emphasises that recombinant therapeutics are "relatively free from risk of infection and immune response" compared to products extracted from animals or human cadavers. This is the single biggest advantage: purity and human compatibility.
Examples you should know (from NCERT and common knowledge) …
Mature insulin's A and B polypeptide chains, produced from a single precursor whose connecting peptide is later removed, remain joined to each other only by a particular sulfur-based …
Mature insulin consists of two polypeptide chains (A and B) held together by disulfide (–S–S–) bonds.
Insulin is synthesised as a single precursor, proinsulin, which contains a connecting (C) peptide. During maturation this C peptide is enzymatically excised, leaving two separate polypeptide chains, chain A (21 amino acids) and chain B (30 amino acids), which remain linked to each other by disulfide bonds formed between cysteine residues on the two chains. This is also why recombinant hum …
Showing the 12 most recent of 26 on this concept.
- CBSE 2026Set 57/1/11 markMCQQ.Assertion (A) : The milk produced by transgenic cow ‘Rosie’ was nutritionally more balanced product for human babies than natural cow milk. Reason (R) : It was human protein enriched milk containing human alpha lactaglobulin. (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation for Assertion (A). (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation for Assertion (A). (C) Assertion (A) is true, but Reason (R) is false. (D) Assertion (A) is false, but Reason (R) is true.
›Reveal solutionSolution
Rosie's milk was enriched with the human protein alpha-lactalbumin, which is precisely why it was more nutritionally balanced for human babies than natural cow milk. Both the assertion and the reason are true and the reason correctly explains the assertion - option (A).
Assertion (A): Rosie's milk was a nutritionally more balanced product for human babies than natural cow milk. This is true - it was the whole purpose of producing Rosie: ordinary cow milk has protein ratios unsuited to human infants, whereas Rosie's milk was engineered to be closer to human milk.
Reason (R): the milk was human-protein-enriched, containing human alpha-lactalbumin. This is also true (the protein named in the paper, written 'alpha lactaglobulin', is a misspelling of alpha-lactalbumin, the human milk protein Rosie's milk was enriched with). Adding this human protein is exactly what made the milk more balanced for babies - so the reason is the correct explanation of the assertion. …
- CBSE 2026Set ANNUAL1 markMCQQ.C-peptide of human insulin is(a) A part of mature insulin molecule(b) Responsible for disulphide bridge formation(c) Removed during maturation of pro-insulin to insulin(d) Responsible for biological activity
›Reveal solutionSolution
Pro-insulin contains an extra connecting (C) peptide that is enzymatically removed to yield mature, biologically active insulin made of the A and B chains.
Insulin is initially synthesised as a single polypeptide precursor called pro-insulin, which contains the A chain, the B chain, and a connecting segment called the C-peptide in between. During post-translational processing/maturation, the C-peptide is enzymatically cleaved off (removed), leaving only the A and B chains, which remain linked together by disulphide bridges to form mature, biologically active insulin.
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- CBSE 2026Set ANNUAL1 markMCQQ.Two polypeptide chains of human insulin are linked to each other :(a) by phosphodiester bonds(b) by convalent bonds(c) by disulphide bonds(d) by hydrogen bonds
›Reveal solutionSolution
The A and B polypeptide chains of mature human insulin are held together by disulphide (S–S) bonds.
Mature human insulin consists of two polypeptide chains — chain A (21 amino acids) and chain B (30 amino acids) — that are covalently linked together by two disulphide bridges (and chain A also has one intra-chain disulphide bond). In the body, insulin is initially synthesised as a single-chain precursor, proinsulin, which contains an extra connecting C-peptide; this C-peptide is enzymatically removed to give the mature, biologically active two-chain insulin he …
- CBSE 2026Set ANNUAL1 markQ.Fill in the blank: Insulin is made up of two short polypeptide chain 'A' and 'B' linked by ______ bonds.
›Reveal solutionSolution
The A and B chains of insulin are joined by disulphide bonds.
Human insulin is a small protein hormone made of two short polypeptide chains, chain A and chain B. These two chains are held together by inter-chain disulphide (S-S) bridges formed between cysteine residues. In the body, insulin is first made as a single chain pro-hormone (pro-insulin) with an extra C-peptide, which is removed during maturation, …
- CBSE 2025Set X11 markMCQQ.Which among the following is an enzyme modified by genetic engineering and used as “Clot buster”?(a) Lipase(b) Pectinase(c) Protease(d) Streptokinase
›Reveal solutionSolution
Streptokinase, a genetically engineered enzyme, is used as a clot buster.
Streptokinase, produced by the bacterium Streptococcus and modified by genetic engineering, is used as a 'clot buster' to dissolve blood clots, for example in patients who have had a myocardial infarction (heart attack). Lipase, pectinase and protease are enzymes used in …
- CBSE 2025Set ANNUAL1 markQ.Write any one example of use of biotechnology in medicine.
›Reveal solutionSolution
A key medical application of biotechnology is producing therapeutic proteins, such as human insulin, using genetically engineered microbes.
Before biotechnology, insulin for diabetics was extracted from the pancreas of slaughtered cattle/pigs, which could cause allergic reactions since it differed slightly from human insulin. Using recombinant DNA technology, the genes for the two insulin chains (A and B) were inserted into E. coli, which then produced human insulin (marketed as Humulin) directly, identical to that made by th …
- CBSE 2025Set ANNUAL1 markQ.If any protein coding gene is expressed in a heterologous host, the protein formed is called _____.
›Reveal solutionSolution
When a cloned, protein-coding gene is expressed in a host organism that is different from its natural source (a 'heterologous host', e.g. a human gene expressed in bacteria), the protein produced is called a recombinant protein.
After a gene of interest has been cloned into a suitable vector and introduced into a host cell for large-scale production (e.g. bacteria or yeast growing in a bioreactor), the host's own transcription and translation machinery is used to express that foreign gene. Because the gene did not originate in that host organism, the protein product is termed a recombinant protein. Not every gene expresses ef …
- CBSE 2025Set ANNUAL1 markMCQQ.During the processing of proinsulin into mature insulin :(a) C peptide is added to proinsulin(b) C peptide is removed from proinsulin(c) B peptide is added to proinsulin(d) B peptide is removed from proinsulin
›Reveal solutionSolution
Proinsulin has an extra connecting (C) peptide that must be enzymatically excised to yield biologically active, two-chain insulin.
Insulin is synthesised as a single inactive polypeptide precursor called proinsulin, which contains the A chain and B chain of mature insulin joined together by an intervening C (connecting) peptide. During post-translational processing, the C peptide is enzymatically cleaved out and removed, leaving the A chain and B chain, which remain linked to each other by disulfide bonds. This two-chain molecule is the mature, biologically active form of insulin. (This is also why recombin …
- CBSE 2025Set ANNUAL1 markQ.What is the name of man-made insulin?
›Reveal solutionSolution
Human insulin produced through genetic engineering (rDNA technology) is marketed as Humulin.
Earlier, insulin used for treating diabetes was extracted from the pancreas of slaughtered cattle and pigs, which sometimes caused allergic reactions in patients because it was not identical to human insulin. Using recombinant DNA technology, the two polypeptide chains of human insulin (chains A and B) were produced separately in E. coli by inserting their respective genes, then extracted and combined by creating disulphide bonds to form active, mature human insulin. This was accom …
- CBSE 2025Set ANNUAL1 markMCQQ.Which biotechnological application is used to produce large quantities of insulin for medicinal purpose ?(a) DNA fingerprinting(b) Gene therapy(c) Polymerase Chain Reaction(d) Recombinant DNA technology
›Reveal solutionSolution
Human insulin (e.g., Humulin) is mass-produced using recombinant DNA technology.
Before biotechnology, insulin was extracted from the pancreas of slaughtered cattle and pigs, causing allergic reactions since it differed slightly from human insulin. Recombinant DNA technology solved this: the human insulin gene (coding for the A and B polypeptide chains) was cloned and inserted into plasmid vectors, which were introduced into Escherichia coli. The bacteria were then cultured in bioreactors to produce the A and B chains separately, which were extracted and combined by forming disulfide bonds to yield …
- CBSE 2025Set ANNUAL1 markMCQQ.Insulin is a hormone produced by beta cell of pancreas. It controls the blood sugar level in the blood by -(i) Converting glycogen into glucose(ii) Converting glucose into glycogen(iii) Converting glucose into galactose(iv) Excretion of sugar by kidneys
›Reveal solutionSolution
Insulin lowers blood glucose mainly by stimulating cells (especially liver and muscle) to convert excess glucose into glycogen for storage (glycogenesis).
Insulin, secreted by the beta cells of the islets of Langerhans in the pancreas, is the principal hormone that lowers blood glucose level. When blood glucose rises (e.g. after a meal), insulin promotes the uptake of glucose by cells and stimulates the liver and muscle cells to convert the excess glucose into glycogen, a storage form of carbohydrate — this process is called glycogenesis. It also promotes glucose utilisation by cells for energy and inhibits glucose production by the liver. This lowers the circulating blood glucose level back towards normal.
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- CBSE 2024Set E1 markMCQQ.What is the use of alpha-1-antitrypsin?(a) In treatment of emphysema(b) In treatment of asthma(c) As insecticidal protein(d) In treatment of diabetes
›Reveal solutionSolution
Alpha-1-antitrypsin is a protein product of biotechnology used in the treatment of emphysema.
Alpha-1-antitrypsin is a protease inhibitor that protects lung tissue from being broken down by the enzyme elastase. A deficiency of this protein leads to emphysema, a chronic lung disease in which the alveolar walls are destroyed. It is one of the products (like insulin) whose deficiency-related disorder …
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