Question

What was the initial evidence for the existence of mRNA?

Short answer

Answer: The key experiments that provided initial evidence for the existence of mRNA as an intermediary molecule between DNA and proteins were conducted by Sidney Brenner, François Jacob, and Matthew Meselson in 1961 and by Elliot Volkin and Lazarus Astrachan in 1956. Brenner, Jacob, and Meselson's work involved using bacteriophages to observe the role of RNA in protein synthesis, while Volkin and Astrachan's work focused on the discovery of a new, short-lived form of RNA associated with infected bacterial cells.

Step-by-step solution

Understanding the central dogma of molecular biology

The central dogma of molecular biology, proposed by Crick in 1958, states that genetic information flows from DNA to RNA and then to proteins. According to this theory, genes (made up of DNA) are transcribed into RNA, and this RNA is then translated into proteins, which carry out various functions in the cell. The hypothesis of an intermediary molecule between DNA and proteins led to the search for messenger RNA (mRNA).

Discussing the key experiments

The initial evidence for the existence of mRNA came from various experiments conducted during the 1950s and 1960s. Here we'll focus on two important ones: the experiments by Brenner, Jacob, and Meselson (1961), and the experiments by Volkin and Astrachan (1956).

Looking at the work of Brenner, Jacob, and Meselson

Sidney Brenner, François Jacob, and Matthew Meselson conducted experiments in 1961 in which they used bacteriophages (viruses that infect bacteria) to observe the role of RNA in protein synthesis. They found that after the initial phase of infection (called the "eclipse phase"), during which no new phage particles could be found, the phage genetic material (DNA) was used to create new phage-specific RNA that was then translated into viral proteins. The newly synthesized RNA only carried the genetic information of the phage, which indicated that it serves as a template for protein production. This was the first direct evidence of mRNA as the intermediary between DNA and proteins.

Discussing the work of Volkin and Astrachan

Elliot Volkin and Lazarus Astrachan in 1956 discovered a previously unknown form of RNA that was specifically associated with infected bacterial cells. They found that this new RNA was rapidly synthesized and then degraded during bacteriophage infection. This led them to hypothesize that this RNA could be a short-lived intermediary molecule carrying genetic information from DNA to proteins, which we now know as messenger RNA (mRNA).

Concluding the initial evidence for the existence of mRNA

Through the work of scientists like Brenner, Jacob, Meselson, Volkin, and Astrachan, the concept of mRNA as a transient carrier of genetic information between DNA and proteins was developed. These groundbreaking experiments provided the foundation for our current understanding of the central dogma of molecular biology and the crucial role that mRNA plays in the flow of genetic information.

Key concepts

Central Dogma of Molecular Biology

The central dogma of molecular biology is a fundamental concept that explains how genetic information is transferred within a biological system. It was proposed by Francis Crick in 1958 and describes the process by which the information in genes (DNA) gets expressed as proteins, which perform various functions needed for life.

The dogma states that the genetic information flows in one direction: from DNA to RNA, and from RNA to proteins. Here's a simplified breakdown of the stages:

• DNA Transcription: The DNA sequence of a gene is transcribed to produce messenger RNA (mRNA). This mRNA acts as a template for reading the genetic code present in DNA.
• RNA Translation: The mRNA is then translated into a protein. Proteins are responsible for a myriad of cellular functions and structures.

The existence of mRNA as an intermediary step was crucial for understanding this flow. Without mRNA, the process of translating genetic information from DNA into functional proteins would not be possible, illustrating how fundamental the central dogma is to molecular biology.

Brenner, Jacob, and Meselson Experiments

In the early 1960s, scientists Sidney Brenner, François Jacob, and Matthew Meselson provided pivotal evidence for the role of mRNA during their research on bacteriophages. Bacteriophages are viruses that infect and replicate within bacterial cells. Their experiments aimed to uncover how genetic information is utilized to produce proteins during phage infections.

They observed that during the initial phase of infection, which they referred to as the "eclipse phase," no new phage particles were produced. However, it was discovered that the phage's genetic material rapidly produced a new type of RNA, distinct from the bacterial RNA, which was used to synthesize viral proteins.
This novel RNA carried the genetic blueprint of the phage alone, demonstrating that it served as a template for creating specific viral proteins. Such findings were groundbreaking as they directly pointed to the concept of mRNA being a carrier of genetic instructions from DNA to proteins. This was the first clear demonstration of mRNA's existence, an intermediary essential for protein synthesis.

Volkin and Astrachan Discovery

Elliot Volkin and Lazarus Astrachan, in 1956, made a significant discovery that laid the foundation for the concept of mRNA. They conducted studies on bacterial cells infected by bacteriophages.

Upon infection, they noted the appearance of a previously unknown form of RNA, which was both rapidly synthesized and degraded. This transient nature was unlike any RNA known at the time and was indicative of its role as a temporary intermediary.
The researchers hypothesized that this fast-turnover RNA was an intermediate molecule in the transfer of genetic information from the phage DNA to the proteins. This was a novel idea back then and complemented Crick's central dogma by suggesting a mechanism whereby genetic information could be transferred and utilized in a short-lived, agile form. This hitherto unknown RNA was later recognized as messenger RNA (mRNA), fulfilling the role of transcriber in the central dogma of molecular biology.