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Your body makes urea every day using a cycle of reactions in the liver, and NEET biology asks you to know its steps. Darshan Ranganathan wanted to do the same chemistry in a flask, with no enzymes, using the same trick nature uses: a carrier molecule that is regenerated at the end of every turn. She managed it, then moved on to designing molecules that build themselves into larger shapes. This post covers her life and science, works through a urea calculation, and ends with what students can learn from her.
Who was Darshan Ranganathan?
The main source here is the tribute to Darshan Ranganathan by D. Balasubramanian in Current Science (2001). She was born in Delhi to Shanti Swarup and Vidyawati Markan and went to school and college there. After a PhD in organic chemistry in T. R. Seshadri's group at Delhi University in 1966, she won a Senior Research Scholarship of the Royal Commission for the Exhibition of 1851 to work with Derek Barton at Imperial College, London.
In London she worked on natural products, including the structure of cycloartenol from jackfruit. Jackfruit was hard to find in London, so her mother shipped it to her from Delhi by the bagful, in dry form. She returned to Delhi in 1969 to teach at a college of Delhi University. In 1970 she married the chemist Subramania Ranganathan and moved to the Indian Institute of Technology, Kanpur, as his research associate.
Why did she work without a faculty post?
Balasubramanian writes that, despite her record, she was never considered for a faculty position at IIT Kanpur. There was no written rule against appointing spouses in the same department, but such a practice was followed implicitly in several Indian institutions. He adds his own view that she would have flowered much earlier had she been given a faculty position. She became a regular staff scientist only later, at the Regional Research Laboratory, Thiruvananthapuram, from 1993 to 1997, and then moved to the Indian Institute of Chemical Technology, Hyderabad, in 1998.
How did she copy the urea cycle in a flask?
The tribute describes two biological processes she simulated chemically. The first was the ATP–imidazole cycle, in which a daughter imidazole molecule was made from a parent imidazole template. The second was the urea cycle, published in 1990 as Urea cycle: chemical simulation of arginine biosynthesis in the Journal of Organic Chemistry.
In her version, a suitably protected ornithine was turned into citrulline using a new amide-transfer reagent. The citrulline was converted into argininosuccinate by an activation method she devised, and that compound was broken down to give urea and regenerate ornithine, the carrier. In other words, she used template and carrier molecules for repeated synthesis, just as cells do. Our guide to excretory products for NEET covers the biological cycle.
Worked example: how much nitrogen does urea carry?
Urea is CO(NH₂)₂, one carbon, one oxygen, two nitrogen and four hydrogen atoms. Using atomic masses C = 12.01, O = 16.00, N = 14.01 and H = 1.008:
Molar mass = 12.01 + 16.00 + 2(14.01) + 4(1.008) = 12.01 + 16.00 + 28.02 + 4.03 = 60.06 g/mol.
Mass of nitrogen per mole = 28.02 g.
Percentage of nitrogen = 28.02 / 60.06 × 100 = 46.7%.
Almost half of urea's mass is nitrogen, which is part of why it works well as a way to get rid of excess nitrogen. Common mistakes. Counting only two hydrogens instead of four, which gives 58.05 g/mol and 48.3%. And forgetting that the formula has two nitrogen atoms, which gives 23.3%, half the right value. Urea also has a famous place in chemistry history; see our profile of Friedrich Wöhler and the synthesis of urea.
What did she build with peptides?
At Thiruvananthapuram and Hyderabad, the tribute says, she turned to designing self-assembling molecular systems. She used rigid building blocks such as norbornene and adamantane, cyclic peptides to fix shape, and residues chosen for hydrogen bonding, so that the molecules arranged themselves into larger structures. She built peptide hairpins, double helices, two-helix bundles, parallel sheets, figure-eight shapes, channel-formers and nanotubes. One example is a 1999 paper in the Journal of the American Chemical Society on hydrogen-bonded peptide nanotubes from cystine-based macrocycles. Hydrogen bonding is the key force, as our guide to hydrogen bonding and intermolecular forces explains.
Her main collaborator was the crystallographer Isabella Karle of the US Naval Research Laboratory. They published about two dozen papers together over more than seven years and, the tribute notes, never met face to face.
She was elected a fellow of the Indian Academy of Sciences in 1991 and of the Indian National Science Academy in 1996, and received the Third World Academy of Sciences Award in Chemistry in 1999. She had been treated for breast cancer in 1997 and 1998; it returned, and she died on 4 June 2001, her sixtieth birthday.
What can a student take from how she worked?
Learn from nature's designs. She took cycles from your biology textbook and asked whether plain chemistry could do the same job.
Keep working when the system is unfair. She did important research for years without a permanent post.
Collaborate generously. Her partnership with Karle produced two dozen papers across continents without the two ever meeting in person.
Know the forces. Hydrogen bonds, which you study in Class 11, were the tools she used to make molecules assemble.
If reaction steps in a cycle are hard to follow, the Fermi Concept Library covers every concept in physics, chemistry, biology, mathematics and computing.
Your next step: draw the urea cycle from your NCERT biology book and mark the one molecule that comes out unchanged at the end.
