By the 1940s it was known that there was another kind of nucleic acid other than DNA, this one called RNA. Phoebus Levene (1869–1940), a Russian-born chemist, further refined the work of Albrecht Kossel (1853–1927). Kossel was awarded the Nobel Prize in Physiology or Medicine in 1910 for determining the composition of nuclein. At the time of Kossel’s work, it was not clear that DNA and RNA were different substances. In 1909, Levene isolated the carbohydrate portion of nucleic acid from yeast and identified it as the pentose sugar ribose. In 1929, he succeeded in identifying the carbohydrate portion of the nucleic acid isolated from the thymus of an animal. It was also a pentose sugar, but it differed from ribose in that it lacked one oxygen atom. Levene called the new substance deoxyribose. These studies defined the chemical differences between DNA and RNA by their sugar molecules.