Celebrating DNA and the History of the Double Helix
April 25 is National DNA Day, a day that commemorates the 60th anniversary of DNA's double helix discovery in 1953 and the completion of the human genome project in 2003. We all boil down, genetically, to chains of DNA—each of us with an individual DNA sequence. Take time this week to talk with your students and kids about DNA, its history, the scientists who helped crack the code, and ways that students at all levels can get hands-on with DNA-related science.When it comes to advancing understanding of genetics and genomics, the discovery of DNA's structure stands as one of the most important turning points in science history. DNA is the blueprint for all organisms, from tiny bacteria to huge whales and long-extinct T. rex dinosaurs.
DNA, and the information it encodes, not only makes each individual organism unique, but also is responsible for certain similarities and traits in groups of organisms. A rose smells the way it does because of DNA. The color of your eyes has something to do with DNA. Whether or not you are at a higher risk of certain health problems may boil down to certain genetic markers you have or do not have. Although genomes (the sum total of DNA needed to encode an organism) are usually copied and acted on in predictable ways, occasionally these mechanisms go awry. Individual stretches of DNA can change or be altered. Transformations, mutations, and other errors in a person's DNA may result in differences in how people respond to a medicine, for example, or may, over long evolutionary time, result in entirely new species.
Encoding the template for a whole organism sounds like a lot of responsibility for a single kind of molecule, but deoxyribonucleic acid (DNA) does just that!
Finding the Double Helix
There were many scientists involved in identifying and isolating DNA and tying it to understanding of heredity and chromosomes. The history of DNA-related discoveries and breakthroughs dates back to the first isolation of DNA by Friedrich Miescher in 1869. Miescher extracted a DNA sample from cast-off, pus-covered bandages. It sounds kind of gross, but Miescher's discovery fueled further research and inquiry. Until the structure of the DNA molecule was established and modeled, however, scientists were unable to fully explain and further explore the role of DNA.
That all changed in 1953.
The publication of both Photo 51, an x-ray diffraction photo (taken in 1952) showing the crystalline structure of DNA, and of a series of papers describing the structure of DNA in Nature in 1953 was a pivotal moment in science. Photo 51 was taken by Rosalind Franklin, a scientist working to create a crystal of the DNA molecule that would enable x-ray diffraction studies and, she hoped, enable her to deduce the structure of DNA. The x-ray pattern captured by Photo 51 revealed, for the first time, the ladder-like structure and winding helix shape we now associate with DNA.
The findings published in the same 1953 issue of Nature as Franklin's photo were from James Watson and Francis Crick. After seeing Franklin's photo, Watson and Crick were able to make a model of DNA that showed the molecule's structure. In 1962, Watson, Crick, and Maurice Wilkins shared the Nobel Prize in Physiology or Medicine for their research on DNA. (Franklin, whose photo may have cracked the code, died in 1958, her contributions then largely unacknowledged.)
April 25 is National DNA Day, a day that commemorates the 60th anniversary of the double helix discovery in 1953 and the completion of the human genome project by the National Human Genome Research Institute (NHGRI) in 2003.
Breaking It Down
You may have played with a model of the DNA structure, or maybe you wear a visual representation on a t-shirt or have a poster or model hanging on your bedroom wall. A helix is defined as "an object having a three-dimensional shape like that of a wire wound uniformly around a cylinder or cone." In most DNA, two helical strands are wound together creating a double helix. Individual DNA molecules (or strands) are each constructed of two long polymers, chains of repeating units made up of pairs of four nucleotides that appear in various repeating combinations. These nucleotides are adenine ("A"), thymine ("T"), guanine ("G"), and cytosine ("C"). These letters give scientists the ABCs (or ATGCs) of DNA—it's a four-letter alphabet which underwrites all known life on Earth!
Armed with knowledge of the structure, composition, and pattern of DNA strands, scientists are able to tackle questions both about history and about the future. Students can, too!
Students "Do" DNA
From fun home activities that let students and parents explore (and show off!) their own DNA to sophisticated projects for advanced student exploration, Science Buddies has a range of Project Ideas that enable students to better understand the role of DNA and encourage them to explore questions related to genetics, genomics, biotechnology, and bioinformatics. You might be surprised at what your fruits and vegetables drawer will yield in terms of visible DNA discovery, but that's just the tip of the genome!
Some DNA-related Science Buddies Project Ideas to explore:
- "Discovering DNA: Do Your Cheek Cells & a Strawberry Both Have DNA?": use a home-friendly Bio-Rad kit to extract and compare DNA from your cheek and from a strawberry.
- "Extracting Onion DNA": extract and spool DNA from an onion using household dishwashing detergent or shampoo.
- "Do-It-Yourself DNA": another procedure to explore DNA extraction with strawberries. .
- "Forensic Science: Building Your Own Tool for Identifying DNA": build a homemade electrophoresis gel chamber and experiment with an important biotechnology procedure often used to separate DNA from other substances.
- "Who Done It? DNA Fingerprinting and Forensics": explore the banding patterns produced in DNA fingerprinting to match a fictitious subject's DNA to a crime scene.
- "What Makes a DNA Fingerprint Unique?": use online tools to compare DNA fingerprints from randomly generated DNA. With only four nucleotides in each DNA, how is everyone's DNA different?
- "Use DNA Sequencing to Trace the Blue Whale's Evolutionary Tree": trace the blue whale's family tree using genomic sequences in the GenBank database and the BLAST search tool.
- "How Much DNA Can You Pack into a Cell?": use online databases to investigate to see if there is a correlation between genome size and cell nucleus size.
- "A Magnetic Primer Designer": experiment with the process scientists use to copy or clone a DNA sample for further study.
- "From Genes to Genetic Diseases: What Kinds of Mutations Matter?": investigate why some gene mutations cause genetic diseases.
- "Drugs & Genetics: Why Do Some People Respond to Drugs Differently than Others?": use an online pharmacogenomics database to research a drug of interest and investigate why a genetic mutation might account for differences in how an individual responds to the drug.
- "The Cancer Genome Anatomy Project": use an online bioinformatics tools to perform "virtual experiments" on real data sets of gene expression data.
- "Trace Your Ancient Ancestry Through DNA": an advanced independent project that lets students explore their DNA history.
Extend the Conversation
There are still questions for scientists to ask and answers to be unlocked through further study of DNA. Just last year, samples of DNA with four strands were discovered. See this article in Nature to shake up your understanding of DNA just a bit. What happens when you square or quad your genetic code?
- For more in-depth information about DNA, see "DNA Is a Structure That Encodes Biological Information".
- For more information about the science history timeline that goes along with DNA, see "Unraveling the Human Genome: 6 Molecular Milestones".
- For new findings about other molecules that can store and pass on genetic information, see "Move over DNA: Six new molecules can carry genes" (New Scientist)