You've probably heard of Watson and Crick. Maybe Rosalind Franklin. But if you ask a molecular biologist who actually settled the question of what genes are made of, they'll tell you about a blender, some radioactive soup, and two people working in a cold room at Cold Spring Harbor in 1952 Simple, but easy to overlook..
One of them was a graduate student named Martha Chase. The other was her boss, Alfred Hershey.
Their experiment didn't just answer a question. It changed how we think about life itself.
What Is the Hershey-Chase Experiment
At its core, the Hershey-Chase experiment was a beautifully simple test: when a virus infects a bacterium, what part of the virus enters the cell? Think about it: the protein coat? Or the DNA inside?
In 1952, that was still an open question. In real terms, seriously. Think about it: smart people argued about it. Protein was complex, versatile, seemed like the obvious candidate for genetic material. DNA? This leads to too simple. Just four bases repeating. How could that carry the instructions for an entire organism?
Quick note before moving on.
Hershey and Chase used bacteriophages — viruses that infect bacteria. It looks like a tiny lunar lander: a protein head packed with DNA, a tail, tail fibers. It lands on E. Specifically, T2 phage. coli, injects something, and hijacks the cell to make more phages No workaround needed..
The question was: what gets injected?
The Radioactive Labeling Trick
Here's the clever part. They grew phages in two separate batches.
One batch grew in medium with radioactive phosphorus-32. So the DNA glowed hot. Phosphorus is in DNA's backbone — not in protein. The protein stayed cold Worth keeping that in mind..
The other batch grew with radioactive sulfur-35. Sulfur shows up in certain amino acids (methionine, cysteine) — so the protein coat got labeled. DNA has no sulfur, so it stayed invisible.
Two populations of phages. Think about it: same shape. On the flip side, same behavior. But one had hot DNA, the other had hot protein.
The Blender Moment
They let the phages infect fresh E. coli. Gave them just enough time to attach and inject — but not enough to replicate Worth knowing..
Then they threw the mixture into a Waring blender. Think about it: literally a kitchen blender. And high speed. Thirty seconds.
The shear force ripped the empty phage coats off the bacterial cells. The coats — mostly protein — stayed in the supernatant. The bacteria, heavier, pelleted at the bottom when spun in a centrifuge.
Now they just had to measure radioactivity in each fraction.
Phages with labeled DNA? The radioactivity went into the pellet. Inside the bacteria.
Phages with labeled protein? The radioactivity stayed in the supernatant. The protein coats never entered.
DNA entered. Protein didn't.
That was it. The genetic material was DNA.
Why It Matters / Why People Care
You might think: okay, cool, a blender experiment. But this was the moment the field turned Turns out it matters..
Before 1952, the Avery-MacLeod-McCarty experiment (1944) had already shown DNA could transform bacteria. Because of that, critics — and there were many — said maybe a trace protein co-purified. But protein contamination couldn't be fully ruled out. Maybe DNA was just a scaffold Surprisingly effective..
Hershey-Chase killed that objection. No purification. No enzymes. Practically speaking, just physical separation. The blender didn't care about biochemistry. It just cared about mass and momentum Most people skip this — try not to..
And the result was unambiguous. Radioactivity doesn't lie It's one of those things that adds up..
The Nobel That Left Her Out
Alfred Hershey shared the 1969 Nobel Prize in Physiology or Medicine with Salvador Luria and Max Delbrück — for their work on phage genetics generally. The Hershey-Chase experiment was cited as a cornerstone And that's really what it comes down to. Turns out it matters..
Martha Chase wasn't included.
She was a research assistant. But she left science not long after, worked in a bakery, later returned to academia in a non-research role. Her name is on the paper — Hershey AD, Chase M — but the Nobel committee didn't recognize her. A technician, officially. She died in 2003 And that's really what it comes down to..
People still argue about it. The era's hierarchy? The fact that she was "just" a grad student? And was it sexism? Probably all of it.
But here's the thing: she did the work. She ran the blenders. That said, she counted the scintillation vials. She made the data.
How It Works — The Experimental Design in Detail
Let's slow down. The blender gets the glory, but the experimental design is what makes it hold up.
Choosing the Right System
T2 phage was perfect. But it has a clear life cycle: attach, inject, replicate, lyse. Plus, the injection step takes minutes. You can catch it mid-act Still holds up..
E. Still, easy to culture. coli grows fast. Easy to pellet.
And the phage structure? Protein outside, DNA inside. That's why no membrane. No lipids to confuse the labeling And that's really what it comes down to..
Why Phosphorus-32 and Sulfur-35
Phosphorus-32 is a beta emitter. Half-life: 14.3 days. Long enough to run the experiment, short enough to decay safely. Incorporates cleanly into DNA via phosphate groups.
Sulfur-35 is also a beta emitter. That said, half-life: 87 days. But gets into methionine and cysteine — amino acids abundant in phage coat proteins. Zero incorporation into DNA Turns out it matters..
Critical point: no crossover. The labeled phages had >99% of radioactivity in the expected macromolecule. On the flip side, they verified this. That purity matters It's one of those things that adds up. Turns out it matters..
The Infection Conditions
They used a high multiplicity of infection — lots of phages per bacterium. Plus, why? Practically speaking, synchrony. They wanted every cell infected at once, so the injection window was tight.
Temperature: 37°C. Standard for E. coli.
Time: 8–10 minutes. Long enough for injection. Short enough that no new phage particles had assembled.
The Blender — Not a Metaphor
A Waring blender. Still, model 31BL91. Still, stainless steel cup. 10,000 rpm.
Why a blender? French press. Even so, hershey had tried other things. Ultrasonic oscillation. They either didn't strip the coats cleanly or they damaged the bacteria Simple, but easy to overlook..
The blender worked. Violent, yes. But the bacteria survived. The phage ghosts — empty protein shells — sheared off clean.
They ran controls. Blended uninfected bacteria? No lysis. Still, blended phages alone? No pellet. The radioactivity distribution only made sense if injection had occurred before blending Easy to understand, harder to ignore..
The Centrifugation Step
Low speed. 10,000 × g for 10 minutes. In real terms, bacteria pellet. Phage coats stay suspended.
They washed the pellet
They washed the pellet three times with a buffered saline solution to strip away any lingering extracellular phage coats. Here's the thing — after the final wash, the bacterial cells were gently resuspended in a low‑salt buffer, then lysed with a detergent that selectively solubilized the proteinaceous cell wall while leaving the nucleic acid intact. The lysate was then centrifuged at a higher speed (30 000 × g, 20 minutes) to separate the soluble DNA from the insoluble protein debris Worth keeping that in mind. Which is the point..
The supernatant, now enriched for DNA, was transferred to a clean tube and its radioactivity measured in a Geiger counter equipped with a thin‑window detector. Think about it: the pellet, containing the residual protein coats, was likewise counted. The results were unambiguous: the majority of the ^32P signal—representing phosphorus‑labeled DNA—resided in the soluble fraction, whereas the ^35S signal—representing sulfur‑labeled protein—remained almost entirely with the pellet Easy to understand, harder to ignore..
When the experiment was repeated with the reverse labeling (i.e., ^35S‑DNA and ^32P‑protein), the pattern flipped: most of the radioactivity was found in the pellet, confirming that the labeling schemes were specific and that no crossover had compromised the assay. The quantitative separation of the two macromolecules provided the decisive evidence that the genetic material of the T2 phage was DNA, not protein.
Why the Design Worked
The brilliance of the Hershey–Chase protocol lay in its simplicity and rigor. Still, by exploiting the distinct chemical compositions of DNA (phosphorus) and protein (sulfur), they created a binary read‑out that could not be easily misinterpreted. The high multiplicity of infection ensured that each bacterium received a phage genome at roughly the same moment, minimizing the confounding effect of asynchronous infection cycles. The blender, far from being a crude kitchen appliance, delivered a precisely controlled shear force that stripped away the protein coat without destroying the bacterial cell, a feat that earlier mechanical methods could not achieve.
The official docs gloss over this. That's a mistake.
On top of that, the experiment was designed with built‑in controls. So naturally, uninfected bacterial pellets showed no ^32P signal, while phage‑only samples yielded no ^35S signal after centrifugation, confirming that the radioactivity measured originated from the infection process itself. The lack of crossover—verified by chemical analysis of the labeled phages—guaranteed that each isotope tracked the intended macromolecule Still holds up..
Impact and Legacy
The 1952 paper, published in the Journal of Experimental Biology, did not immediately overturn the prevailing view that proteins were the carriers of genetic information. C. Miller for their discoveries concerning the genetic material. In 1962, Alfred Hershey shared the Nobel Prize in Physiology or Medicine with Marcel E. At the time, the notion that DNA could be the hereditary molecule was still contested, and the Hershey–Chase work was one of several converging lines of evidence that eventually led to the acceptance of DNA as the genetic material. M. So nobel laureate Marvin C. The omission of Martha Chase from the award remains a point of discussion among historians of science, emblematic of the broader challenges faced by women in mid‑century research laboratories.
Modern Reflections
Contemporary molecular biology owes a debt to the experimental ingenuity of Hershey and Chase. Because of that, their use of radioactive isotopes foreshadowed the power of tracer studies that now dominate fields from virology to genome editing. Modern adaptations of their approach—using fluorescent tags, CRISPR‑based reporters, and high‑throughput sequencing—still rely on the same principle: distinguishing nucleic acids from proteins to answer fundamental biological questions Small thing, real impact..
The story of Martha Chase also serves as a reminder that scientific progress is rarely a linear narrative. Her contributions, though central, were obscured by institutional biases and the hierarchical structures of the era. Revisiting her role enriches our understanding of how collaborative and diverse scientific teams shape discovery.
Conclusion
Hershey and Chase’s meticulous experiment—blending, centrifuging, and counting radioisotopes—delivered a clean, quantitative answer to one of biology’s most profound questions: what transmits hereditary information? In real terms, by demonstrating that DNA, not protein, entered the bacterial cell during infection, they provided the final piece of evidence that cemented DNA’s status as the molecule of inheritance. Their work not only transformed our conceptual framework but also set a standard for experimental rigor that continues to guide research today. In the end, the legacy of that 1952 laboratory is measured not only in Nobel Prizes but in the very DNA that encodes life itself.
This is where a lot of people lose the thread And that's really what it comes down to..
