Question

When Avery and his colleagues had obtained what was concluded to be the transforming factor from the IIIS virulent cells, they treated the fraction with proteases, ribonuclease, and deoxyribonuclease, followed by the assay for retention or loss of transforming ability. What were the purpose and results of these experiments? What conclusions were drawn?

Short answer

Answer: The purpose of treating the fraction with proteases, ribonuclease, and deoxyribonuclease in Avery and his colleagues' experiments was to determine the nature of the transforming factor. This allowed them to deduce which type of molecule was responsible for the transformation. From the experiments, they concluded that the transforming factor in the virulent IIIS cells was DNA, as the transforming ability was lost when treated with deoxyribonuclease, providing significant evidence that DNA carries genetic information in living organisms.

Step-by-step solution

Understanding the experiments

To identify the transforming factor in the virulent IIIS cells, Avery and his colleagues performed a series of experiments. They treated the fraction, which was thought to contain the transforming factor, with proteases, ribonuclease, and deoxyribonuclease. Then, they assayed the treated fraction for the retention or loss of transforming ability.

Explaining the purpose of treating the fraction with different enzymes

The purpose of treating the fraction with proteases, ribonuclease, and deoxyribonuclease was to determine the nature of the transforming factor. Proteases break down proteins, ribonuclease breaks down RNA molecules, and deoxyribonuclease breaks down DNA molecules. By treating the fraction with these enzymes and observing the retention or loss of transforming ability, they could deduce which type of molecule was responsible for the transformation.

Discussing the results of the experiments

After the fraction was treated with proteases and ribonuclease, the transforming ability remained, indicating that proteins and RNA were not the transforming factors. However, when the fraction was treated with deoxyribonuclease, the transforming ability was lost. These results showed that the transforming factor was sensitive to deoxyribonuclease, indicating that the transforming factor was most likely DNA.

Concluding the experiments

From the results of these experiments, Avery and his colleagues concluded that the transforming factor in the virulent IIIS cells was DNA. This was a groundbreaking discovery, as it showed that DNA, not proteins or RNA, was responsible for carrying genetic information and could cause the transformation in bacteria. The conclusions of these experiments provided significant evidence to support the understanding of DNA as the genetic material in living organisms.

Key concepts

Transforming Factor

In the early 20th century, scientists were puzzled about what component in cells carried genetic information. Frederick Griffith's experiments first hinted at the idea of a "transforming factor," which could transfer traits from one bacterial strain to another. However, the exact nature of this transforming factor remained a mystery until Oswald Avery and his team conducted their renowned experiments.

Avery's research primarily focused on the virulent IIIS bacterial cells, believed to contain the transforming factor. By isolating a fraction from these cells, they hoped to identify the component responsible for genetic transformation. This fraction was then treated with different enzymes to determine its molecular nature. Through their careful experiments, Avery and his colleagues systematically tested the properties of this elusive factor.

• After treatment with proteases (which break down proteins), the transforming ability was not affected, eliminating proteins as the transforming factor.
• Similarly, when treated with ribonuclease (which degrades RNA), the transforming ability persisted, ruling out RNA.

Thus, Avery's methodical approach set the stage for a pivotal discovery in molecular biology, pointing directly to the transforming factor's identity.

Deoxyribonuclease

Deoxyribonuclease, often abbreviated as DNase, plays a crucial role in Avery's experiments. This enzyme specializes in breaking down DNA molecules. By applying DNase to their isolated fraction, Avery and his colleagues aimed to see whether DNA was the mystery molecule responsible for transformation.

The results were telling. Once the fraction was treated with deoxyribonuclease, the transforming ability was fully lost. This indicated that the molecule necessary for the transformation of bacterial cells had been degraded, thus confirming its identity as DNA. As proteins and RNA did not affect transformation, DNase was the definitive test. This discovery was groundbreaking, providing the strongest evidence at the time that DNA was indeed the transforming factor.

This insight into the function of deoxyribonuclease was crucial, as it allowed scientists to conclusively prove that DNA carried genetic information, challenging previous beliefs that proteins, given their complexity, were the primary genetic material.

Genetic Material

The concept of genetic material changed fundamentally with the findings of Avery and his team. Before their pivotal discovery, the main contenders for the hereditary material were proteins. Due to the diverse structure and function of proteins, many believed they were responsible for genetic information.

However, Avery's experiments radically shifted this perspective. By demonstrating that DNA was the transforming factor, they provided concrete evidence that DNA was the material carrying genetic instructions in cells. This revelation paved the way for future discoveries in genetics and molecular biology, ultimately leading to our understanding of DNA's crucial role.

Key impacts of identifying DNA as genetic material include:

• Confirmation of DNA as the hereditary material in living organisms.
• Foundation for the discovery of the structure of DNA by Watson and Crick a decade later.
• Inspiration for exploring DNA replication, transcription, and translation processes.

Thus, Avery's work not only solved the mystery of the transforming factor but also opened new frontiers in biological research, firmly establishing DNA as the cornerstone of genetics.