DNA/RNA Era 1960-1970

After DNA and it’s shape was discovered, researchers have been struggling to figure out how the DNA from a nucleus makes new proteins throughout the cell. It was in 1961 that Sydney Brenner and Francis Crick made the hypothesis that RNA was the messenger of DNA, that it brings the templates for building proteins in ribosomes. This idea was confirmed by Brenner and François Jacob whilst they were working with E. coli.

Francis Crick and Sydney Brenner made another discovery in 1961. That discovery was that the genetic code is a triplet code. Meaning that for each amino acid there is three bases coding it. They came to this conclusion by mutating the DNA of the bacteriophage known as T4. The mutations caused bases of the DNA to be inserted or deleted. They observed that after two or four mutations took place, the gene that makes the bacteriophage infect bacteria stopped working. But when three mutations took place, the gene began working again.

Yet another discovery was made in 1961. Jacques Monod, François Jacob, and Arthur Pardee wondered how it was possible that every cell has the same DNA but different types of cells make different proteins, this is known as gene regulation. They figured this answer out by experimenting with a type of E. coli that produces β-galactosidase under varying conditions. Their experimentation resulted in answer that the production system of enzymes was controlled by another system that controlled it. That system contained what they called an ‘Operator’ and ‘Repressor’. One of the two became active based off of the cell’s environment or genetic commands.

1961 was a very productive year because another discovery was made by Mary Lyon. While experimenting with mice, she noticed that the female offspring of a normal dark mouse and a white mouse with the X chromosome being inactive had speckled fur. She came to the conclusion that this was because while in the stages of early development, one of the each pairs of X chromosomes inside female mouse cells, and her descendants are not active. It was realized that the cause of this was because of the more dense ‘Barr bodies’ inside the female mammal cells. Subsequently, this process was called X chromosome inactivation, also called ‘lyonisation’. The discovery that Lyon made was very significant to gaining an understanding of how human inherited disorders work.

 It was 1966 when the most important discovery in genetics of the decade, or maybe of all time was made, the genetic code was finally cracked. The question of how specific codes of DNA and RNA from it, provide the blueprints for making the amino acids that were then assembled into proteins was answered. The first part of the code was discovered by Marshall Nirenberg and Heinrich Matthael in 1961. They had developed a synthetic version of RNA. Their synthetic only used one of the four nulceotides in RNA, uracil. It enacted the production of the protein that was made of a single amino acid called phenylalanine. They discovered that the codons, UUU, for the RNA, what we would say ‘spells out’ phenylalanine. Other researchers took on the task of finding out the rest of the genetic codes. The most important of those researchers was Har Gobind Khorana. It was in 1966 that his work was completed. Francis Crick invented a table that showed how each of letters that represented the codons of RNA spell out one of the amino acid, or what’s called a ‘nonsense codon’ which is just a codon that marks the end of a sequence.

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