Question

Discuss the reasons why 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: Before 1940, scientists favored proteins as genetic material due to their complexity, functionality, and abundance in cells compared to DNA. The tetranucleotide hypothesis, which incorrectly suggested that DNA had a simple and repetitive structure, further supported the belief that proteins, as more complex molecules, were more suited to carry genetic information. However, this hypothesis was later proven false, ultimately leading to the understanding that DNA is the genetic material.

Step-by-step solution

Reasons for favoring proteins as genetic material

Prior to 1940, proteins were considered to be the genetic material for a number of reasons: 1. Complexity: Proteins are made up of 20 different amino acids, while DNA is made up of only four nucleotides (adenine, guanine, cytosine, and thymine). This led scientists to believe that proteins, with their higher variability, would be better suited to carry the complex genetic information required for the development and function of living organisms. 2. Functionality: Proteins play a wide range of roles in cells, serving as enzymes, structural components, and signaling molecules, among other functions. At the time, DNA was thought to be a static molecule with no active role beyond the storage of genetic information. 3. Abundance: Proteins are abundant in cells, making them more likely to be observed in experiments. Because DNA is located within the nucleus, it was not as easily detected by early research techniques.

The tetranucleotide hypothesis

The tetranucleotide hypothesis played a significant role in the controversy over the identity of genetic material. This hypothesis, proposed by Phoebus Levene in the early 20th century, suggested that the four DNA nucleotides—adenine (A), guanine (G), cytosine (C), and thymine (T)—were present in equal amounts in a single repeating unit, or tetranucleotide. The tetranucleotide hypothesis supported the idea that DNA was too simple to be the genetic material. If the four nucleotides were present in equal amounts and simply repeated in a fixed pattern, there would not be enough complexity in DNA to encode the vast amount of genetic information needed to specify the structure and function of all biological molecules and processes. As a result, the tetranucleotide hypothesis contributed to the prevailing belief that proteins, not DNA, were the genetic material. However, this hypothesis was later proven false with the discovery that the composition of DNA varies between species and even between different tissues within the same organism. This led to the later understanding that DNA, not proteins, is the genetic material.