Everything Everywhere Daily: History, Science, Geography & More - The Discovery of DNA

Episode Date: March 6, 2024

One of the most important advancements in the 20th century was the identification of the structure of the DNA molecule. However, that discovery didn’t appear out of nowhere. It was part of a century-long process that included many advancements in biology, chemistry, and physics.  Solving the secret of the DNA molecule was a major accomplishment, but it wasn’t without controversy. Learn more about the discovery of DNA and how its structure was solved on this episode of Everything Everywhere Daily. Sponsors Sign up today at butcherbox.com/daily and use code daily to choose your free offer and get $20 off. Visit BetterHelp.com/everywhere today to get 10% off your first month. Use the code EverythingEverywhere for a 20% discount on a subscription at Newspapers.com. Subscribe to the podcast!  https://link.chtbl.com/EverythingEverywhere?sid=ShowNotes -------------------------------- Executive Producer: Charles Daniel Associate Producers: Peter Bennett & Cameron Kieffer   Become a supporter on Patreon: https://www.patreon.com/everythingeverywhere Update your podcast app at newpodcastapps.com Discord Server: https://discord.gg/UkRUJFh Instagram: https://www.instagram.com/everythingeverywhere/ Facebook Group: https://www.facebook.com/groups/everythingeverywheredaily Twitter: https://twitter.com/everywheretrip Website: https://everything-everywhere.com/ Learn more about your ad choices. Visit megaphone.fm/adchoices

One of the most important advancements in the 20th century was the identification of the structure of the DNA molecule. However, that discovery didn't appear out of nowhere. It was part of a century-long process that included many advancements in biology, chemistry, and physics. And while solving the secret of the DNA molecule was a major accomplishment, it wasn't without controversy. Learn more about the discovery of DNA and how its structure was solved on this episode of Everything Everywhere Daily.

What if your perceptions about the past were wrong? ThruLine is a podcast that takes you back in time to uncover the parts of the story that may have gone unnoticed. It effectively turned day into night. And how it shaped the world now. Time travel with us every week on the ThruLine podcast from NPR. It is hard to stress just how important DNA is. DNA stands for deoxyribonucleic acid, and it's the foundation of all life as we know it. You have DNA, your pets have DNA, trees have DNA, amoebas have DNA, and so do viruses.

DNA literally defines what life is on Earth. Analyzing DNA has been used to diagnose illnesses, solve crimes, and create new drugs. The discovery of DNA and how it functions is one of the most of the most of the most of the most important scientific discoveries of all time. Yet it wasn't discovered in an aha moment. It was a process that spanned over a century and in some respects is still going on today. There were two discoveries made in the 19th century that seemed to have nothing to do with each other at the time, but it later turned out that they were intimately related. The first discovery is one you might have heard of. It was made by an Austrian monk named

Grigor Mendel. He conducted exceptional. experiments with pea plants at his abbey in Bruno in what is today the Czech Republic. For centuries, humans have known that certain physical traits can be passed from one generation to the next, whether it's in humans, animals, or crops. Through the meticulous crossbreeding of 28,000 pea plants from 1856 to 1864, he observed how traits were passed down through generations, leading him to formulate the laws of inheritance, including the concepts of dominant and recessive traits, and the segregation of pairs of traits.

Mendel's work was largely ignored during his lifetime, but was rediscovered later when its importance was realized. The second 19th century discovery was made by a Swiss biochemist by the name of Friedrich Meisher. Mischer was investigating the nuclei of white blood cells when he isolated several chemical compounds found inside. The chemicals he isolated were rich in phosphates, and he dubbed them nucleic acids, because they came from the cell's nucleus. Meishur's process for collecting the cells and isolating the nucleus was very innovative, and it all actually began with collecting pus from discarded surgical bandages.

Meishir had no idea what nucleic acids did, and Gregor Mendel had no idea of the molecular process by which the traits he discovered were transmitted. In 1902, a Danish biologist by the name of Wilhelm Johansson demonstrated that discrete units of heredity determined inheritance through experiments he did on pure lines of beans. He showed that while environmental factors can influence the phenotype, in other words, the observable traits of an organism, the genotype or the genetic makeup remained unchanged and is responsible for the hereditary transmissions. Johansson's work helped to distinguish between the genetic constitution of an organism

and the expression of those genes, emphasizing the role of genetics in determining hereditary traits and laying the groundwork for the field of genetics as a scientific discipline. It was Johansen who coined the terms gene, phenotype, and genotype. In the 1910s and 1920s, Phoebus Levine, a researcher at the Rockefeller Institute in New York, identified the basic components of nucleic acids, like DNA, which he dubbed nucleotides, each one consisting of a sugar, a phosphate group, and a nitrogen base. In DNA, there are four known nucleotides, adenine, guanine, cytosine, and thymine. The next big advancement came in 1928.

Frederick Griffith, a British bacteriologist, made a groundbreaking discovery in the field of genetics through his experiment on Streptococcus pneumonia, the bacteria responsible for pneumonia. Griffith conducted what is now known as the Griffith experiment, where he demonstrated the phenomenon of transformation. He found that a harmless strain of the bacteria could be transformed into a virulent one when mixed with heat-killed virulent bacteria. This transformation was due to the transfer of genetic materials from the dead bacteria to the living ones, making them virulent. Griffith's work provided the first evidence of horizontal gene transfer and suggested that some transforming principle was responsible for heredity. That transformers,

principle had to be a molecule. In 1927, Russian biologist Nikolai Koltsov proposed that whatever transmitted hereditary information had to be transmitted via a very large molecule using, quote, two mere strands that would replicate in a semi-conservative fashion using each strand as a template. So at this point, on the one side, there were researchers who had identified DNA and even figured out what it was composed of. And on the other side, other researchers identified how heredity worked and how heredity had to be transvited via some molecule. What was needed was someone to tie these two things together. That happened in 1944. A team of researchers who worked at the

Rockefeller Institute, Oswald Avery, Colin McLeod, and Macklein McCarty made the leap that put everything together. They set out to find the molecule that was responsible for encoding and passing heredity. They did something similar to Frederick Griffith's experiments almost 20 years earlier. In their experiment, they extracted various biochemical components from the virulent strain of streptococcus pneumonia and treated non-verulent bacteria with these components. They discovered that only the purified DNA from the virulent bacteria could transform the non-veralant strain into a virulent form.

This transformation demonstrated that DNA, and not protein or some other molecule was the substance carrying genetic information. Their work marked a pivotal moment in biology by providing the first clear evidence that DNA was the molecule of heredity, setting the stage for the future discoveries of the structure of DNA and the development of molecular genetics. In fact, many people believe that this discovery is one of the most important discoveries of the 20th century that was never awarded a Nobel Prize. In 1952, Alfred Hershey and Martha Chase conducted a different experiment that confirmed the findings of Avery McLeod and McCarty, that DNA is indeed the genetic molecule.

Also, in the late 40s and early 50s, Erwin Chargaff, working at Columbia University, developed a series of rules for how the components of DNA all fit together. He found that in any given DNA molecule, the amount of adenine always equals the amount of thymine, and the amount of guanine. and the amount of guanine always equals the amount of cytosine. This one-to-one ratio held true across various species and became a crucial piece of evidence for the structure of DNA. Charghoff's rule suggests that A pairs with T and G pairs with C,

which helped explain how genetic information is stored and replicated in living organisms, contributing to the understanding of DNA's roles in heredity. So by the early 1950s, a big part of the mystery of heredity had, had been solved. Deoxyribonucleic acid had been identified as the molecule that transmitted genetic information. Many of the laws of heredity had been figured out, and even the chemical components of DNA were now known. However, there was still much that they didn't understand, such as how exactly did DNA transmit genetic information? If it was indeed a large molecule that replicated itself using two identical strands, how did that work? To understand all of this,

it was necessary to determine the shape and structure of the DNA molecule. One team that took this problem on were two researchers at Cambridge University, Englishman Francis Crick and American James Watson. They developed a model for the structure of DNA that involved a double helix shape. They used the rules developed by Chargaff to build physical models of the molecule that would fit the known rules of how the molecule was built and worked. On February 28, 1953, Crick got up at a positive, in Cambridge and announced to all of the patrons and attendance that he and Watson had discovered

the secret to life. On April 8th, they made the first public presentation in Belgium at a conference where they announced their findings. However, their discovery did not warrant a mention in the press anywhere. It wasn't until an article was published in the journal Nature on April 25th that attention was finally given to their discovery. At the top of the show, I mentioned that the discovery of DNA had controversy, and it was in Watson and Crick's announcement that the controversy set in. Perhaps the key single piece of evidence used by Watson and Crick was a photograph taken by another Cambridge researcher, Rosalind Franklin, using X-ray spectography. The historic photo became known as Photograph 51.

The image was able to put Watson and Crick on the right path in creating a DNA model, and by their own later admission, it probably wouldn't have been possible without it. However, they didn't get Franklin's permission to use her research, nor did they even notify her that they had used it. The photograph was given to them by Maurice Wilkins, another researcher in the same lab, who was doing X-ray spectrography on DNA. Rosalind Franklin died in 1958, and Watson, Crick, and Wilkins were awarded the Nobel Prize in physiology in 1962. The Nobel Prize Committee doesn't award prizes posthumously, so Franklin couldn't have gotten the award, but her contributions to the discovery of the discovery of the, shape of DNA wasn't made public until well after her death. The discovery of the double helix wasn't the end of DNA discoveries.

In fact, it really just marked the beginning of an entire new field of study. In 1958, American molecular biologist Matthew Messelson and Franklin Stahl conducted an experiment that confirmed DNA could replicate via a process known as semi-conservative replication. They showed that each strand in double helix DNA could split, split and be paired with a new strand, thus replicating into two new DNA molecules. The first full DNA sequence was performed by the British biochemist Frederick Sanger in 1977. Sequencing is when the complete ordering of all of the AT, C, and G nucleotides is recorded.

Sanger did a DNA sequence for a simple bacteria and was awarded his second Nobel Prize in 1980. His first Nobel Prize came in 1958 for determining the amino acid sequence of of insulin. It wasn't until 2003 that the first human genome sequence was finally conducted. It took 13 years from 1990 to 2003 to sequence most of the human genome, and it was one of the largest collaborative science projects in history. The very last gaps in the genome weren't completed, however, until January 2022, 32 years after the project started. In 2012, a technique was developed for editing and changing DNA molecules. Known as CRISPR, it's a technique taken from the immune system of bacteria. CRISPR stands for the clustered, regularly interspaced, short palindromic

repeats. The name was created in 2001 to make it easier to understand. Jennifer Dowdna of the United States and Emmanuel Charpentier of France were awarded the 2020 Nobel Prize for the development of CRISPR technology. In many ways, DNA research and technology are really really. just getting started. The techniques for manipulating and editing DNA are still recent developments, and there are plenty of discoveries in advances yet to be made. However, all of the modern uses of DNA stemmed from discoveries made in the 19th century by researchers who had no clue about the importance of what they had stumbled upon. The executive producer of Everything Everywhere Daily is Charles Daniel. The associate producers are Peter Bennett and Cameron Kiefer. I wanted to give a big

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