Question

Discuss the reasons proteins were generally favored over DNA as the genetic material before $1940.$ What was the role of the tetranucleotide hypothesis in this controversy?

Short answer

Answer: Proteins were favored over DNA as the genetic material before 1940 due to their diverse structures, vast array of functions, and seemingly endless potential for complexity, while DNA appeared much simpler in structure. The tetranucleotide hypothesis, which proposed that DNA was made up of repeating units of the same sequence of the four nucleotide bases, further strengthened the belief that DNA’s simplicity made it unlikely to carry genetic information. This hypothesis hindered the understanding of DNA's true structure and function. It wasn't until later discoveries in the 1940s and 1950s that the true complexity and role of DNA as the genetic material were revealed, leading to the dismissal of the tetranucleotide hypothesis.

Step-by-step solution

Provide historical background on proteins and DNA as genetic material

Before the pivotal experiments in molecular biology in the 1940s, scientists had limited understanding of the role that nucleic acids (including DNA) and proteins played in inheritance. Proteins, with their diverse structures and vast array of functions, were seen as the more likely candidate for carrying genetic information because they appeared to be more complex compared to the simpler structure of nucleic acids.

Discuss the complexity and diverse roles of proteins

Proteins are composed of amino acids, which can be arranged in a countless number of combinations to create a wide variety of structures and functions within a cell. Proteins perform most of the work within cells, including catalyzing reactions, providing structural support, and transporting various molecules. Given the diverse role of proteins and their seemingly endless potential for complexity, it might have appeared more reasonable to assume that proteins were responsible for transmitting genetic information.

Explain the simplicity and misunderstandings of DNA structure

DNA, on the other hand, appeared much simpler in structure in comparison to proteins. DNA is composed of nucleotides, with each nucleotide containing a phosphate group, a sugar molecule, and one of four nitrogenous bases: adenine, cytosine, guanine, or thymine. Early chemists who studied DNA believed that the four nucleotide bases were present in equal quantities, which led to the formation of the tetranucleotide hypothesis.

Explain the tetranucleotide hypothesis and its impact on the controversy

The tetranucleotide hypothesis proposed that DNA was made up of repeating units of the same sequence of the four nucleotide bases (A, C, G, and T), which would result in a simple, repetitive structure rather than the complex, information-rich molecule needed to carry genetic information. This hypothesis hindered the understanding of DNA's true structure and function and allowed scientists to continue believing that proteins were the carriers of genetic information.

Conclude the discussion with the shift in scientific understanding

It wasn't until decisive experiments by Avery, MacLeod, and McCarty in 1944, followed by Hershey and Chase in 1952, that it became clear that DNA was the genetic material. Furthermore, the discovery of the double helix structure of DNA by Watson and Crick in 1953 revealed that DNA indeed possesses a complex structure capable of carrying genetic information. This shift in scientific understanding dispelled the tetranucleotide hypothesis and solidified DNA's role as the primary genetic material, thus resolving the controversy surrounding proteins and DNA as genetic material.