Which scientist is credited with discovering and describing the monomers (nucleotides) of nucleic acids?

Introduction / Context:
The history of nucleic acid research involves several key discoveries made by different scientists. First, researchers identified nucleic material itself, later they understood its chemical components, and eventually they worked out its structure and function as genetic material. This question focuses on who is credited with discovering and describing the monomers of nucleic acids, known as nucleotides, which are essential building blocks of DNA and RNA.

Given Data / Assumptions:

Nucleic acids are built from repeating units called nucleotides.
Each nucleotide contains a sugar, phosphate group, and nitrogenous base.
Several scientists listed contributed to different aspects of nucleic acid research.

Concept / Approach:
Friedrich Miescher was the first to isolate a substance he called nuclein from cell nuclei, now recognized as crude nucleic acid. Watson and Crick, working with data from Rosalind Franklin and others, proposed the double helix model of DNA structure. Gerardus Johannes Mulder and Jons Jacob Berzelius worked on protein chemistry. Phoebus Levene, however, analyzed nucleic acids in detail and identified that they are made of repeating nucleotide units. He described the components of nucleotides such as sugar, phosphate, and bases and proposed early structural ideas, even though some of his specific conclusions were later revised. Therefore, Levene is most closely associated with discovering and defining nucleotides as the monomers of nucleic acids.

Step-by-Step Solution:
Step 1: Match each scientist or group with their major contribution to nucleic acid chemistry or genetics. Step 2: Recognize that Miescher first extracted nucleic material but did not fully describe the nucleotide structure. Step 3: Recall that Watson, Crick, and Franklin focused on DNA double helix structure, not the original discovery of nucleotide monomers. Step 4: Identify Phoebus Levene as the chemist who defined nucleotides as repeating units with sugar, phosphate, and base, making him the correct choice.

Verification / Alternative check:
Historical summaries of DNA research often list milestones in sequence. After Miescher isolated nuclein, Levene analyzed this material and identified distinct nucleotide components, before later researchers like Chargaff, Franklin, Watson, and Crick clarified base ratios and three dimensional structure. This chronological order supports the idea that Levene is specifically associated with the discovery and detailed description of nucleotides.

Why Other Options Are Wrong:
Watson, Crick, and Franklin: They contributed to the structural model of DNA but did not first identify nucleotide monomers.
Friedrich Miescher: He discovered nucleic material in nuclei but did not define nucleotide components in detail.
Mulder and Berzelius: Their main work was in protein chemistry rather than nucleic acid nucleotide structure.

Common Pitfalls:
Students sometimes credit the most famous names in DNA research for all related discoveries. It is important to distinguish between the discovery of nucleic material, the recognition of nucleotides, and the double helix model. Remembering that Phoebus Levene worked out the basic nucleotide structure helps keep this history clear.

Final Answer:
The scientist credited with discovering and describing nucleic acid monomers is Phoebus Levene.