Phoebus Levene, a Russian-born American biochemist, was a pivotal figure in early 20th-century science. His work focused on deciphering the chemical makeup of biological molecules, especially DNA and RNA. Levene’s research provided foundational insights, though some initial theories were later revised. His meticulous analysis laid groundwork for understanding the molecules of heredity.
Unraveling Nucleic Acid Components
Levene investigated and identified the chemical building blocks of nucleic acids. He isolated three primary components: phosphate groups, five-carbon sugars, and nitrogenous bases. This analysis revealed adenine, guanine, cytosine, and thymine in DNA, and adenine, guanine, cytosine, and uracil in RNA. His carbohydrate chemistry expertise helped distinguish the sugars in these molecules. This identification of components advanced understanding of DNA and RNA’s chemical nature.
Proposing the Nucleotide Structure
Building on identifying components, Levene proposed the basic structural unit of nucleic acids. He termed these units nucleotides, consisting of a phosphate group, a five-carbon sugar, and a nitrogenous base linked together. This tripartite structure was a major advance in biochemistry. Levene suggested these nucleotide units joined through their phosphate groups, forming the nucleic acid chain’s backbone.
The Tetranucleotide Hypothesis Explained
One of Levene’s most influential, yet incorrect, theories was the tetranucleotide hypothesis. Proposed around 1910, it suggested DNA was composed of repeating units of four specific nucleotides—adenine (A), thymine (T), cytosine (C), and guanine (G)—in a fixed, simple, and equal ratio. Levene believed this repetitive structure implied DNA was too simple to carry complex genetic information, leading him and others to mistakenly think proteins were the carriers of heredity. This idea was widely accepted for decades, diverting attention from DNA’s true role.
Distinguishing DNA from RNA
Levene chemically differentiated DNA and RNA. He identified the specific five-carbon sugar in DNA as deoxyribose and the sugar in RNA as ribose. Levene observed DNA contains thymine, while RNA contains uracil. These chemical distinctions established DNA and RNA as separate types of nucleic acids, paving the way for research into their unique biological functions.
Levene’s Enduring Legacy
Despite the refutation of his tetranucleotide hypothesis by Erwin Chargaff, Levene’s fundamental discoveries advanced molecular biology. His identification of nucleic acid components and proposal of the nucleotide as their basic structural unit laid essential groundwork. Levene’s work established nucleic acid chemistry, providing a foundation for breakthroughs. Researchers like Erwin Chargaff, whose rules contradicted the tetranucleotide hypothesis, and James Watson and Francis Crick, who discovered the DNA double helix, built upon Levene’s chemical insights.