Q.C-peptide of human insulin is:
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)
- Insulin (Humulin): First recombinant therapeutic. Used for diabetes.
- Human Growth Hormone: For children with growth deficiency.
- Erythropoietin (EPO): Stimulates red blood cell production; used for anaemia.
- Factor VIII: Clotting factor for haemophilia A.
- Monoclonal Antibodies: Used in diagnostics and targeted cancer therapy (e.g., Trastuzumab for breast cancer).
A quick mental model
Think of it like a custom bakery. Instead of hunting wild animals for a rare ingredient, you take the recipe (the gene) for the exact cake you want, give it to a baker (the host cell) that can make it perfectly every time, and then scale up production in a factory (the fermenter). The result is a consistent, safe, and abundant supply of the exact product you need.
In short: Recombinant protein therapeutics = using genetically modified microbes as living factories to produce human proteins as medicines. It is the foundation of modern biopharmaceuticals.
Recombinant protein therapeutics is part of the NCERT Class 12 Biology chapter on Biotechnology and its Applications, and is commonly searched as "recombinant protein therapeutics examples class 12" or "biotechnology applications in medicine important questions." This is also a favourite topic for NEET biology, since insulin and other recombinant drugs are asked about almost every year.
Human insulin is initially synthesized as proinsulin, a single-chain precursor that contains three segments: the A-chain, B-chain, and a connecting peptide called the C-peptide. The C-peptide links the A and B chains during the folding process, allowing the correct disulphide bridges to form between cysteine residues on the A and B chains.
Once the disulphide bonds are properly established and the molecule is correctly folded, the C-peptide is enzymatically cleaved and removed. What remains is the mature, biologically active insulin molecule consisting only of the A and B chains held together by disulphide bridges. The C-peptide itself does not appear in the final functional insulin and plays no role in insulin's biological activity—it is simply a structural aid during biosynthesis.
In recombinant insulin production, scientists often express the A and B chains separately in bacteria and then combine them chemically, bypassing the proinsulin stage altogether. This confirms that the C-peptide, while helpful in natural biosynthesis, is not part of the active hormone.
The C-peptide is removed during the maturation of proinsulin to insulin and is not part of the mature, biologically active molecule—(C) is correct.
The C-peptide is a connecting segment in pro-insulin that is cleaved off during maturation, leaving behind the functional two-chain insulin molecule held together by disulphide bridges.
When we talk about recombinant insulin production—one of the landmark achievements in biotechnology—we need to understand how insulin is naturally made in the human body. Insulin isn't synthesized directly as the active hormone we know. Instead, it goes through a precursor stage called pro-insulin, and this is where the C-peptide comes into the picture.
Pro-insulin is a single-chain polypeptide that contains three regions: the A-chain, the B-chain, and the C-peptide (the "C" stands for "connecting"). The C-peptide sits between the A and B chains, literally connecting them during the folding process. As pro-insulin folds inside the pancreatic beta cells, disulphide bridges form between specific cysteine residues—two bridges connect the A and B chains, and one bridge forms within the A-chain itself. These disulphide bonds are crucial because they stabilize the three-dimensional structure of the molecule.
Here's the key transformation: once the disulphide bridges are properly formed and the molecule is correctly folded, the C-peptide has done its job. It is then enzymatically removed by specific proteases. What remains is mature insulin—a two-chain structure (A-chain and B-chain) held together by those disulphide bridges. The C-peptide itself is released into the bloodstream along with insulin but has no role in insulin's biological activity of regulating blood glucose.
In clinical practice, measuring C-peptide levels helps doctors assess how much insulin a person's pancreas is still producing, since C-peptide and insulin are released in equimolar amounts.
So let's evaluate the options. The C-peptide is not part of the mature insulin molecule—it's removed before insulin becomes functional. It doesn't directly form the disulphide bridges; rather, it holds the chains in proximity while those bridges form spontaneously during folding. It certainly isn't responsible for biological activity—that belongs to the mature A-B chain structure. What the C-peptide does is get removed during the maturation process, which is exactly what option (C) states.
The C-peptide is removed during the maturation of pro-insulin to insulin, after it has served its purpose of keeping the A and B chains together while disulphide bridges form. The correct answer is (C).
Method — picture pro-insulin as three beads on a string
A-chain — C-peptide — B-chain, held by disulphide bonds forming between A and B during folding.
Maturation = cut out the middle bead (C-peptide) once A and B are correctly cross-linked.
So: C-peptide's job is purely structural/scaffolding during folding; it is removed, not part of the final hormone, and has no biological activity of its own → (c).
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.
ImportantA transgenic animal carries and expresses a deliberately introduced foreign gene; Rosie expressed the human alpha-lactalbumin gene in her mammary tissue, secreting the human protein into her milk.
✓Final answer(A) Both Assertion (A) and Reason (R) are true, and Reason (R) correctly explains Assertion (A). (The printed 'alpha lactaglobulin' is a misprint for alpha-lactalbumin and does not change the answer.)
- 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.
So the C-peptide is NOT part of mature insulin, is not itself what forms the disulphide bridges (those form between the A and B chains), and is not responsible for insulin's biological activity — its role is only in ensuring correct folding of pro-insulin before being cleaved away.
✓Final answer(c) Removed during maturation of pro-insulin to insulin.
- 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 held together by disulphide bonds. This detail was crucial for producing recombinant human insulin (Humulin) by expressing the A and B chains separately in E. coli and then joining them via disulphide bonds in vitro.
✓Final answer(c) by disulphide bonds.
- 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, leaving the mature A and B chains linked by disulphide bonds. This structure was important in genetically engineering human insulin (Humulin).
✓Final answerDisulphide (S-S) bonds.
- 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 other applications (fat digestion, fruit-juice clarification and protein breakdown respectively) and are not clot busters.
✓Final answer(d) Streptokinase
- 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 the human pancreas — a landmark example of biotechnology's use in medicine. (Gene therapy, e.g., for ADA deficiency, is another valid example.)
✓Final answerProduction of human insulin (Humulin) using genetically engineered bacteria.
- 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 efficiently or produces a biologically active protein in a heterologous host, which is why optimisation and downstream processing steps are needed before the protein can be used (e.g. as a biopharmaceutical such as insulin or growth hormone).
✓Final answerRecombinant protein.
- 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 recombinant-DNA-produced human insulin, e.g. Eli Lilly's Humulin, is made by separately synthesising the A and B chains in E. coli and then joining them via disulfide bonds — mimicking the natural C-peptide removal step.)
✓Final answer(b) C peptide is removed from proinsulin.
- 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 accomplished by Eli Lilly, and the product was marketed under the brand name Humulin — the first genetically engineered, man-made insulin approved for human use (1983).
✓Final answerHumulin — human insulin produced by recombinant DNA technology in E. coli.
- 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 functional human insulin (Humulin), the first recombinant pharmaceutical product approved for human use. DNA fingerprinting, PCR and gene therapy are related biotech tools but are not what is used to mass-produce insulin.
✓Final answer(d) Recombinant DNA technology.
- 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.
(A related, well-known Class-12 biotechnology application is the production of recombinant human insulin — Humulin — using genetically engineered E. coli, which produces the A and B chains of human insulin separately, which are then extracted and combined by disulphide bonds.)
✓Final answerInsulin controls blood sugar by converting glucose into glycogen (Option ii).
- 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 disorders are being corrected using genetically engineered protein therapy. NCERT lists it among proteins produced to treat such disorders.
✓Final answer(a) In treatment of emphysema.
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