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Your NCERT Class 11 chapter on the cell gives the Na+/K+ pump as the standard example of active transport: moving ions against their concentration gradient using ATP. Someone had to find the molecule that does it. That was Jens Skou, a surgeon-in-training who started out studying local anaesthetics. This post covers how he found the pump, how it works and a calculation that shows why it makes the inside of a cell lose positive charge.
Who was Jens Skou?
His Nobel Prize facts page gives his dates: born on 8 October 1918 in Lemvig, Denmark, and died on 28 May 2018 in Aarhus. He shared the 1997 Nobel Prize in Chemistry "for the first discovery of an ion-transporting enzyme, Na+, K+ -ATPase".
In his Nobel autobiography, Skou describes studying medicine in Copenhagen during the German occupation and qualifying in 1944. In hospital he became interested in how local anaesthetics act, and in 1947 he moved to the Institute of Medical Physiology at Aarhus University to write a thesis on it. "I had no scientific training when I started at the Institute of Physiology in 1947," he wrote. The anaesthetic work led him to the pump, and his paper on it appeared in 1957.
How did he find the pump?
The Nobel press release sets out the background. In the early 1950s Alan Hodgkin and Richard Keynes had shown that sodium ions pour into a nerve cell when it fires, and that the cell then transports the sodium back out. Blocking ATP production stopped that transport, so ATP was probably the fuel.
Skou went looking for an ATP-splitting enzyme in nerve membranes that could be linked to this transport. He used finely ground crab nerve membranes. The enzyme he found:
needed magnesium ions;
was stimulated by sodium ions, up to a limit;
was stimulated further when a little potassium was added;
worked fastest at the sodium and potassium levels normally found in nerve.
That last point suggested the enzyme was the pump itself. He published it as The influence of some cations on an adenosine triphosphatase from peripheral nerves in Biochimica et Biophysica Acta. The press release calls it the first enzyme shown to drive directed transport of a substance across a cell membrane.
How does the pump work?
The press release describes the cycle that later work established:
Three sodium ions and one ATP bind on the inside face of the enzyme.
A phosphate group moves from ATP onto an aspartic acid in the enzyme, and ADP leaves.
The enzyme changes shape and releases the sodium ions outside.
Two potassium ions bind from outside.
The phosphate is removed and the potassium ions are carried inside.
The same release says that at rest this one enzyme uses about a third of all the ATP the body makes. Digitalis-type drugs such as ouabain block it.
A worked example: counting ions and charge
Take sample numbers: suppose the pumps in one cell together split 1.0 × 10⁶ ATP molecules per second.
Sodium out: 3 × 1.0 × 10⁶ = 3.0 × 10⁶ ions per second.
Potassium in: 2 × 1.0 × 10⁶ = 2.0 × 10⁶ ions per second.
Net positive charges out: 3.0 × 10⁶ − 2.0 × 10⁶ = 1.0 × 10⁶ per second.
Current: 1.0 × 10⁶ × 1.6 × 10⁻¹⁹ C = 1.6 × 10⁻¹³ A.
Reverse question: how many ATP are needed to move 6.0 × 10⁶ sodium ions out? 6.0 × 10⁶ ÷ 3 = 2.0 × 10⁶ ATP, which also brings 4.0 × 10⁶ potassium ions in.
Common mistakes to avoid:
Writing 1:1 or 2:3. It is 3 Na+ out and 2 K+ in per ATP.
Calling the pump a channel. Channels let ions flow down a gradient; the pump uses ATP to push them up one.
Saying the pump alone makes the negative inside. The press release explains that potassium leaking out through the membrane leaves negative charges behind; the pump keeps the high potassium inside that makes this possible.
Why does it matter for nerves and cells?
The press release explains that the voltage across the membrane is needed for impulses to travel along nerve and muscle cells. If oxygen or nutrients run out in the brain, ATP production stops, the pump stops and a person quickly loses consciousness. Without the pump a cell swells. The sodium gradient it builds also powers uptake of glucose and amino acids. For how nerves use these gradients to fire, read our post on Hodgkin, Huxley and the action potential.
Related pumps were found later, including the H+,K+-ATPase that makes stomach acid. Together they are called P-type ATPases because they are phosphorylated during each cycle.
What can a student take from Skou's way of working?
Skou followed a question from his clinical work into a field he had no training in, and chose a tissue, crab nerve, that made the experiment possible. He also kept firm hours: "I am a family man, I restricted my work at the Institute to 8 hours a day," he wrote, and he "worked concentratedly" while he was there.
Short, focused sessions work for revision too. If the steps of active and passive transport blur together, the Fermi Concept Library covers every concept in biology and chemistry, one idea at a time. Our guide to transport across the cell membrane covers the NCERT side.
Next step: draw the five-step pump cycle from memory, then check the number of ions and the charge moved in each step.
