David Baltimore introduces the different types of viruses, and defines how viruses are classified depending on their genetic material. Using HIV as an example, Baltimore explains what constitutes an equilibrium versus a non-equilibrium virus, and shows how the discovery of the reverse transcriptase helped scientists understand viruses.

In an extended video, Baltimore outlines the sequence of events that led to the discovery of reverse transcriptase, an enzyme that converts a sequence in an RNA molecule into a sequence in a DNA molecule. As Baltimore explains, the discovery of reverse transcriptase has revolutionized modern molecular biology, and it has aided in the understanding of viruses like HIV, and the genetic basis of cancer.

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An introduction to viruses

Extended video: Introduction to viruses and the discovery of reverse transcriptase