 Have you ever heard of the central dogma of biology? It's the concept that genetic information stored as DNA gets turned into RNA, a process called transcription, which gets turned into protein. The idea that the flow of information is unidirectional was put forth by Francis Crick in 1958. The very word dogma means that this is the truth, a fact. So can you imagine challenging this established truth? Well, in the 1970s, scientists found an exception to the central dogma. These scientists were studying viruses and they realized that some viruses called retroviruses use RNA and not DNA to store their genetic information. This is different from most other organisms. Why was this interesting to scientists? And how did it lead to their questioning of the central dogma? To answer this, let's first talk about retroviruses. Retroviruses are small particles that consist of genetic information and a few proteins inside a capsule. These viruses need to be inside the cell of another host organism to replicate. Once inside, viruses copy their genetic material to form many more viruses. Scientists knew how DNA was copied to make more DNA. They also knew how DNA was copied to make RNA. But retroviruses posed a puzzle. How can the RNA in these viruses be copied? Back in the early 1970s, David Baltimore and Howard Teman hypothesized that retroviruses might have a special kind of enzyme, a polymerase, that could turn their RNA into DNA. So they went on a search for this enzyme. First, the scientists isolated a candidate enzyme that could use an RNA template and make a product. But what was the product? Was it copies of DNA or of RNA? To answer this question, they combined the purified enzyme with the RNA template and different kinds of nucleotides to be incorporated into the new product. If the nucleotides given were ribonucleotides, the building blocks of RNA, no product was produced. If instead they gave deoxyribonucleotides, the building blocks of DNA, they could get a product. This strongly suggested that the viral polymerase was converting the RNA template into a DNA product and not an RNA product. Information was flowing in the opposite direction that Francis Crick had proposed in the central dogma. This enzyme was later named reverse transcriptase because it does transcription, but backwards. This exciting new discovery earned Baltimore and Tevin the Nobel Prize in 1975. Baltimore and Tevin's finding had a major impact on modern medicine and biotechnology. Before the modern genomic era, the identification of most human genes involved copying human RNA into DNA by reverse transcriptase to be used for further studies. Another important example is HIV, the retrovirus that causes AIDS and affects 35 million people worldwide. HIV uses reverse transcriptase to replicate and spread. Thanks to Baltimore and Tevin's discovery, physicians now use medicines that block reverse transcriptase to treat patients with HIV. And all of this from questioning the dogma.