Author: chemistadmin

Rosalind Franklin’s role in the discovery of the structure of DNA may have been different than previously believed. Franklin wasn’t the victim of data theft at the hands of James Watson and Francis Crick, say biographers of the famous duo. Instead, she collaborated and shared data with Watson, Crick and Maurice Wilkins.

Seventy years ago, a trio of scientific papers announcing the discovery of DNA’s double helix was published. Watson, Crick and Wilkins won the Nobel Prize in physiology or medicine in 1962 for the finding. Franklin, a chemist and X-ray crystallographer, died of ovarian cancer before the prize was awarded and was not eligible to be included.

Many people have been outraged by accounts that Watson and Crick used Franklin’s unpublished data without her knowledge or consent in making their model of DNA’s molecular structure. What’s more, Franklin supposedly did not understand the significance of an X-ray diffraction image, taken by her graduate student, that came to be known as Photograph 51. Wilkins showed the image to Watson, who is said to have instantly recognized it as proof that DNA forms a double helix. And the rest is history.

Except that history is wrong, say Watson and Crick biographers Nathaniel Comfort and Matthew Cobb. Cobb is a zoologist at the University of Manchester in England, and Comfort, of Johns Hopkins University, is a historian of science and medicine. They uncovered historical documents among Franklin’s papers that they say should change the view of her contribution to the discovery.

Among the documents was an unpublished article from Time magazine depicting Watson and Crick as a team collaborating with Franklin and Wilkins, who were working as a pair. Overlooked letters and a program from a presentation to the United Kingdom’s Royal Society reinforced the idea that Franklin was a willing colleague who understood her data. The researchers laid out their findings in a commentary in the April 27 Nature.

Cobb and Comfort talked with Science News about their new view of Franklin’s contributions. The conversation has been edited for length and clarity.

SN: Why did you decide to go through these documents?

Comfort: Matthew’s writing this biography of Crick, and I am writing a biography of Watson…. And we decided as a kind of pilgrimage to go and see the Franklin papers in person….

We weren’t expecting really anything other than just sort of a perfunctory visit when we sat down in this archive room together, and they pulled out the folders. We started going over them together, bouncing ideas back and forth saying, “Hey, what’s this?”

The sparks started flying, and that was when we found this magazine article from Time that was never published. It was a very rough draft that the author, named Joan Bruce, had sent to Franklin for fact-checking to make sure she got the science right.

Cobb: So what Nathaniel immediately picked up on in the Bruce article was the way that she presented the discovery. She presents it as being an equal piece of work — that the two groups, at King’s [College with Franklin and Wilkins] and at the Cavendish [Laboratory with Watson and Crick] in Cambridge, are effectively collaborating….

It’s not [the story] we’re used to hearing because the version we have is the dramatic Jim Watson version from his book The Double Helix: “Ha-ha! I stole their data!… Little did they know but I had it in my hands.” This is dramatic reconstruction.

Comfort: If it were this way [as in Bruce’s article], it actually gives the lie to Watson’s sensational account. And we know why — or at least I think I know why — Watson gave that sensational account.

The audience for The Double Helix was intended to be high school and college students who he wanted to get excited about science.… And I have lots of examples from that book where he stretches the truth, where he takes liberties, where he takes literary license. And I can show that as a pattern through the entire book. So it also fits with the style and tone of The Double Helix.

SN: Is there other evidence that Watson and Crick didn’t steal her data?

Cobb:  What we have separately done by looking in real detail at the records — the interviews that Crick did in the ’60s and so on — is we’ve been able to reconstruct the process that [Watson and Crick] went through. Which, if you read their papers really carefully, actually says quite explicitly that they engaged in what they called a process of trial and error. So they knew roughly the size of the crystal of the DNA molecule. They knew the atoms that should be in there from the density. So they tried to fit this stuff into this size using chemical rules.

Then there’s this report [on X-ray diffraction data] that was written by the King’s researchers, Franklin and Wilkins, as part of their funding from the Medical Research Council. It was shared with other laboratories, including the head of the laboratory in Cambridge, Max Perutz [Crick’s boss]. And this is all known, so we haven’t discovered this. Watson and Crick used some of the numbers in there from Franklin and Wilkins as a kind of check on their random walk-through of possible structures….

This still looks like kind of underhand, right? Because they’ve been given this semi-official document. Then two things happened. Firstly, if you read their documents, it’s quite clear that they do explain that they had access to this document, and that they used it as a check on their models. So this fact is acknowledged at the time….

We then stumbled upon a letter from a Ph.D. student who was at King’s College, called Pauline Cowan, who was a friend of Crick’s…. So Cowan writes this letter asking him for help with something completely uninteresting. Then she says in passing, “Franklin and Gosling” — that’s Franklin’s Ph.D. student who took Photograph 51 — “are giving a seminar on their data.” This is in January 1953. “You can come along if you want. Here’s the details. But they say that they’re not really going to go into much detail. It’s for the general lab audience, and Perutz knows all the results anyway. So you might not want to bother coming.”

In other words, Franklin knows that Watson and Crick will have access to this informal report, and she doesn’t care. It’s all, “Hey, if you want it, that’s fine.” So that then shifts the optic away from they got this surreptitious access to this MRC report. So we’re back to this collaborative [picture]. Franklin doesn’t seem to be too bothered.

And then the final element … we found a program of a Royal Society exhibition…. This is two months after the publication of the papers. [In the program] is a brief summary of the structure of DNA signed by everybody, presented by Franklin.

It was like a school science fair. She’s standing there in front of a model explaining it to everybody, and all their names are on it. So this isn’t a race that’s been won by Watson and Crick. I mean, they did get there first, don’t get us wrong. But it wasn’t seen that way at the time. They could not have done it without the data from Franklin. And Wilkins. And everybody — at least at this stage in 1953 — is accepting that and seems okay with it.

Just like the Joan Bruce article said. So this changes the mood, right? We’re moving away from the Hollywood thriller that Watson wrote, where he’s sneaked some data. That version is really exciting. It’s just not true. [We’re moving] to something that’s much more collaborative, modern in some respects, about sharing data.

Today, we focus on Franklin because we’re currently interested in equality, women’s oppression, and so on. We’re also obsessed with DNA. But people weren’t back then. DNA wasn’t then what it is now. [People might think] how could Franklin not have been livid? This was the secret of life and she had had it taken away from her. But it wasn’t and she didn’t.

SN: Did Franklin understand the importance of her data?

Cobb: Franklin was very skilled at being able to move DNA between two forms; what’s called the A form, which is the crystalline form which gives really precise images, and what’s called the B form. That form is what you get if there’s much more water around the molecule kind of pulling it into a different shape. And it was very clear from her notes that she thought that the B form was basically the loss of order, that it was disintegrating….

If you study the double helix story, there’s this this kind of enigma, because there are these two forms, A and B.  Franklin studies the A form … [but] it’s never been clear to anybody why she chose that form. And then we realized it’s because she’s a crystallographer. She’s a chemist. And if you’re a chemist, and you’re trying to find the crystalline structure of something, what are you going to look at? The crystal.

It’s easy in retrospect to get in a time machine and go back and whisper in her ear, “Hey, but what’s the inside of the cell like? It’s not very dry, you know. Maybe think about the other form.” But … you can’t do that. That’s against the rules….

Everybody who wants to favor Rosalind Franklin thinks that Watson and Crick were kind of sexist pigs who stole her data. The first bit of that description is probably accurate. The second bit isn’t. They certainly were pretty rude. But they did not steal the data.

This is the popular version of the story which we wanted to undermine. That this Photograph 51, which is the B form, is so striking that Watson, when he’s given a glimpse of it, can instantly realize its significance. According to the story he tells and people who are in favor of Franklin tell, this is the moment he steals her data.

But if you think about it for a minute, you think, “Well, why didn’t Franklin get it if it’s so obvious? This really smart woman who’s much smarter than Watson is about this aspect of science, but she doesn’t get it?” And the answer is very clear when you read her notes. She did get it and she didn’t care. She knew it was some kind of helix, but that was not the structure that interested her.

What [the popular story] does is it removes any agency from Franklin. People are inadvertently presenting her as a negative version, the version that Watson presents. She’s the heroine, but she hasn’t gotten it yet. Why hasn’t she got it? Well, the only implication is what Wilkins says; that she was stubborn and blinkered, which is just not true. So we’re trying to put her back at the center of the story, make her much more human than this harridan that Watson presents her as.

SN: Do we know if Franklin complained at the time about her data being stolen?

So after the double helix [discovery], Franklin and Wilkins never question Watson and Crick, “How did you do this?” They never fall out with them. They never have a row. They never write anything. Either they were stupid and never asked the question, or they knew [that the data were shared fairly].

Then in [19]54, for example, Franklin’s going to the East Coast to go to this meeting on the West Coast that Watson’s going to as well. And so she writes to Watson, “Dear Jim, I gather you’re getting a car across the states. Can I come with you?” So she tried to hitch a ride on a transcontinental car journey with this man who supposedly had stolen life’s secret from under her nose. That doesn’t make sense.

She was on collegial terms — I don’t think she liked him — but she was on collegial terms with Jim…. They had extensive correspondence because they were in the same area of viral structure.

In the last two or three years of her life, she became very good friends with Crick and with his wife. They went on holiday together in Spain after a conference. After she had her first two operations for ovarian cancer, she went to the Cricks to convalesce. She would send Crick her draft articles and ask his advice. So she clearly didn’t think he was a pig who was going to steal all of that data.

SN: So they were just much more chill about the whole thing?

Cobb: They were all much more chill. We look at this, one, through a feminist optic. We being the world. It’s an inverse version of The Double Helix. And, two, through the optic of what would it be like today to discover this? Clearly, you’d have competing labs, they would not talk to each other, and if one of them had these data, then they would behave exactly like Watson describes it.

But that was not the world of the 1950s. Partly because DNA was not DNA. It wasn’t clear that it was the genetic material [of life]. So it wasn’t a big deal.

On Franklin’s tomb there is no mention of DNA. What there is mention of is viruses.  Because that’s the practical work that she was engaged in when she died. She had worked out the structure of the polio virus. DNA wasn’t a practical thing for another 20 years. Whereas the structure the polio virus, maybe that could save lives.

The way we see her is not how she was seen at the time. She was very famous. She got a page obituary in Nature, obituaries in Britain’s the Times and the New York Times. So many of her American colleagues were utterly distraught when they discovered that she died [in 1958]. So you know, she was a very significant person, not just for DNA.

SN: Dr. Watson is still living. Have you spoken with him or anyone else who’s still around that could offer some insight?

Comfort: I’ve spoken with him many times, and he knows about this project. But he’s not in any [physical] shape right now to be able to comment on something like this. Believe me, I would love to, but it’s just not possible.

Art historians often wish that Renaissance painters could shell out secrets of the craft. Now, scientists may have cracked one using chemistry and physics.

Around the turn of the 15th century in Italy, oil-based paints replaced egg-based tempera paints as the dominant medium. During this transition, artists including Leonardo da Vinci and Sandro Botticelli also experimented with paints made from oil and egg (SN: 4/30/14). But it has been unclear how adding egg to oil paints may have affected the artwork.  

“Usually, when we think about art, not everybody thinks about the science which is behind it,” says chemical engineer Ophélie Ranquet of the Karlsruhe Institute of Technology in Germany.

In the lab, Ranquet and colleagues whipped up two oil-egg recipes to compare with plain oil paint. One mixture contained fresh egg yolk mixed into oil paint, and had a similar consistency to mayonnaise. For the other blend, the scientists ground pigment into the yolk, dried it and mixed it with oil — a process the old masters might have used, according to the scant historical records that exist today. Each medium was subjected to a battery of tests that analyzed its mass, moisture, oxidation, heat capacity, drying time and more.

In both concoctions, the yolk’s proteins, phospholipids and antioxidants helped slow paint oxidation, which can cause paint to turn yellow over time, the team reports March 28 in Nature Communications. 

In the mayolike blend, the yolk created sturdy links between pigment particles, resulting in stiffer paint. Such consistency would have been ideal for techniques like impasto, a raised, thick style that adds texture to art. Egg additions also could have reduced wrinkling by creating a firmer paint consistency. Wrinkling sometimes happens with oil paints when the top layer dries faster than the paint underneath, and the dried film buckles over looser, still-wet paint.

The hybrid mediums have some less than eggs-ellent qualities, though. For instance, the eggy oil paint can take longer to dry. If paints were too yolky, Renaissance artists would have had to wait a long time to add the next layer, Ranquet says.

“The more we understand how artists select and manipulate their materials, the more we can appreciate what they’re doing, the creative process and the final product,” says Ken Sutherland, director of scientific research at the Art Institute of Chicago, who was not involved with the work.

Research on historical art mediums can not only aid art preservation efforts, Sutherland says, but also help people gain a deeper understanding of the artworks themselves.

In August 2021 on a lonely crater floor, the newest Mars rover dug into one of its first rocks.

The percussive drill attached to the arm of the Perseverance rover scraped the dust and top several millimeters off a rocky outcrop in a 5-centimeter-wide circle. From just above, one of the rover’s cameras captured what looked like broken shards wedged against one another. The presence of interlocking crystal textures became obvious. Those textures were not what most of the scientists who had spent years preparing for the mission expected.

Then the scientists watched on a video conference as the rover’s two spectrometers revealed the chemistry of those meshed textures. The visible shapes along with the chemical compositions showed that this rock, dubbed Rochette, was volcanic in origin. It was not made up of the layers of clay and silt that would be found at a former lake bed.

Nicknamed Percy, the rover arrived at the Jezero crater two years ago, on February 18, 2021, with its sidekick helicopter, Ingenuity. The most complex spacecraft to explore the Martian surface, Percy builds on the work of the Curiosity rover, which has been on Mars since 2012, the twin Spirit and Opportunity rovers, the Sojourner rover and other landers.

But Perseverance’s main purpose is different. While the earlier rovers focused on Martian geology and understanding the planet’s environment, Percy is looking for signs of past life. Jezero was picked for the Mars 2020 mission because it appears from orbit to be a former lake environment where microbes could have thrived, and its large delta would likely preserve any signs of them. Drilling, scraping and collecting pieces of the Red Planet, the rover is using its seven science instruments to analyze the bits for any hint of ancient life. It’s also collecting samples to return to Earth.

Since landing, “we’ve been able to start putting together the story of what has happened in Jezero, and it’s pretty complex,” says Briony Horgan, a planetary scientist at Purdue University in West Lafayette, Ind., who helps plan Percy’s day-to-day and long-term operations.

Volcanic rock is just one of the surprises the rover has uncovered. Hundreds of researchers scouring the data Perseverance has sent back so far now have some clues to how the crater has evolved over time. This basin has witnessed flowing lava, at least one lake that lasted perhaps tens of thousands of years, running rivers that created a mud-and-sand delta and heavy flooding that brought rocks from faraway locales.

Jezero has a more dynamic past than scientists had anticipated. That volatility has slowed the search for sedimentary rocks, but it has also pointed to new alcoves where ancient life could have taken hold.

Perseverance has turned up carbon-bearing materials — the basis of life on Earth — in every sample it has abraded, Horgan says. “We’re seeing that everywhere.” And the rover still has much more to explore.

Perseverance finds unexpected rocks

Jezero is a shallow impact crater about 45 kilo­meters in diameter just north of the planet’s equator. The crater formed sometime between 3.7 billion and 4.1 billion years ago, in the solar system’s first billion years. It sits in an older and much larger impact basin known as Isidis. At Jezero’s western curve, an etched ancient riverbed gives way to a dried-out, fan-shaped delta on the crater floor.

That delta “is like this flashing signpost beautifully visible from orbit that tells us there was a standing body of water here,” says astrobiologist Ken Williford of Blue Marble Space Institute of Science in Seattle.

Perseverance landed on the crater floor about two kilometers from the front of the delta. Scientists thought they’d find compacted layers of soil and sand there, at the base of what they dubbed Lake Jezero. But the landscape immediately looked different than expected, says planetary geologist Kathryn Stack Morgan of NASA’s Jet Propulsion Laboratory in Pasadena, Calif. Stack Morgan is deputy project scientist for Perseverance.

For the first several months after the landing, the Mars 2020 mission team tested the rover’s movements and instruments, slowly, carefully. But from the first real science drilling near the landing location, researchers back on Earth realized what they had found. The texture of the rock, Stack Morgan says, was “a textbook igneous volcanic rock texture.” It looked like volcanic lava flows.

Over the next six months, several more rocks on the crater floor revealed igneous texture. Some of the most exciting rocks, including Rochette, showed olivine crystals throughout. “The crystal fabric was obviously cooled from a melt, not transported grains,” as would be the case if it were a sedimentary sample, says Abigail Allwood of the Jet Propulsion Lab. She leads the rover’s PIXL instrument, which uses an X-ray beam to identify each sample’s composition.

Mission scientists now think the crater floor is filled with igneous rocks from two separate events — both after the crater was created, so more recently than the 3.7 billion to 4.1 billion years ago time frame. In one, magma from deep within the planet pushed toward the surface, cooled and solidified, and was later exposed by erosion. In the other, smaller lava flows streamed at the surface.

Sometime after these events, water flowed from the nearby highlands into the crater to form a lake tens of meters deep and lasting tens of thousands of years at least, according to some team members. Percy’s instruments have revealed the ways that water altered the igneous rocks: For example, scientists have found sulfates and other minerals that require water to form, and they’ve seen empty pits within the rocks’ cracks, where water would have washed away material. As that water flowed down the rivers into the lake, it deposited silt and mud, forming the delta. Flooding delivered 1.5-meter-wide boulders from that distant terrain. All of these events preceded the drying of the lake, which might have happened about 3 billion years ago.

Core samples, which Perseverance is collecting and storing on board for eventual return to Earth, could provide dates for when the igneous rocks formed, as well as when the Martian surface became parched. During the time between, Lake Jezero and other wet environments may have been stable enough for microbial life to start and survive.

“Nailing down the geologic time scale is of critical importance for us understanding Mars as a habitable world,” Stack Morgan says. “And we can’t do that without samples to date.”

About a year after landing on Mars, Perseverance rolled several kilometers across the crater floor to the delta front — where it encountered a very different geology.

The delta might hold signs of ancient life

Deltas mark standing, lasting bodies of water — stable locales that could support life. Plus, as a delta grows over time, it traps and preserves organic matter.

Sand and silt deposited where a river hits a lake get layered into sedimentary material, building up a fan-shaped delta. “If you have any biological material that is trapped between that sediment, it gets buried very quickly,” says Mars geologist Eva Scheller of MIT, a researcher with the Percy team. “It creates this environment that is very, very good for preserving the organic matter.”

While exploring the delta front between April 2022 and December 2022, Perseverance found some of the sedimentary rocks it was after.

Several of the rover’s instruments zoomed in on the textures and shapes of the rocks, while other instruments collected detailed spectral information, revealing the elements present in those rocks. By combining the data, researchers can piece together what the rocks are made of and what processes might have changed them over the eons. It’s this chemistry that could reveal signs of ancient Martian life — biosignatures. Scientists are still in the early stages of these analyses.

There won’t be one clear-cut sign of life, Allwood says. Instead, the rover would more likely reveal “an assemblage of characteristics,” with evidence slowly building that life once existed there.

Chemical characteristics suggestive of life are most likely to hide in sedimentary rocks, like those Perseverance has studied at the delta front. Especially interesting are rocks with extremely fine-grained mud. Such mud sediments, Horgan says, are where — in deltas on Earth, at least — organic matter is concentrated. So far, though, the rover hasn’t found those muddy materials.

But the sedimentary rocks studied have revealed carbonates, sulfates and unexpected salts — all materials indicating interaction with water and important for life as we know it. Percy has found carbon-based matter in every rock it has abraded, Horgan says.

“We’ve had some really interesting results that we’re pretty excited to share with the community,” Horgan says about the exploration of the delta front. Some of those details may be revealed in March at the Lunar and Planetary Science Conference.

Perseverance leaves samples for a future mission

As of early February, Perseverance has collected 18 samples, including bits of Mars debris and cores from rocks, and stored them on board in sealed capsules for eventual return to Earth. The samples come from the crater floor, delta front rocks and even the thin Martian atmosphere.

In the final weeks of 2022 and the first weeks of 2023, the rover dropped — or rather, carefully set down — half of the collected samples, as well as a tube that would reveal whether samples contained any earthly contaminants. These captured pieces of Mars are now sitting at the front of the delta, at a predetermined spot called the Three Forks region.

If Perseverance isn’t functioning well enough to hand over its onboard samples when a future sample-return spacecraft arrives, that mission will collect these samples from the drop site to bring back to Earth.

Researchers are currently working on designs for a joint Mars mission between NASA and the European Space Agency that could retrieve the samples. Launching in the late 2020s, it would land near the Perseverance rover. Percy would transfer the samples to a small rocket to be launched from Mars and returned to Earth in the 2030s. Lab tests could then confirm what Perseverance is already uncovering and discover much more.

Meanwhile, Percy is climbing up the delta to explore its top, where muddy sedimentary rocks may still be found. The next target is the edge of the once-lake, where shallow water long ago stood. This is the site Williford is most excited about. Much of what we know about the history of how life has evolved on Earth comes from environments with shallow water, he says. “That’s where really rich, underwater ecosystems start to form,” he says. “There’s so much going on there chemically.”