1940 - Phoebus Levene died.

National Institutes of Health

Levene was a Russian-American biochemist who discovered nucleic acids came in two different forms called DNA and RNA based on ribose and deoxyribose. He identified the components of DNA where it contained adenine, guanine, thymine, cytosine, deoxyribose and a phosphate group. He also determined these components linked together as phosphate-sugar-base units he called nucleotides. He believed the structure of DNA was based on a tetranucleotide where the different components were equally distributed.