DNA/RNA Era ~1950-1960

Before this man came along, no one knew how amino acids were arranged in chains or how to find them. In 1951, Fred Sanger found a solution to that problem. The method Fred invented worked as follows: First the amino acids located at the ends of fragmented proteins are labelled with levels of radiation. Next the fragments are separated using a process called Paper chromotography, which involves using paper to separate different pigments or chemicals. The results of the paper chromotography are then recorded on photographic film. The last step is analyzing the content of the different amino acids in each fragment of protein. After all this, Fred was able to completely reconstruct the full sequencers of the chains.

Alfred Hershey and Martha Chase were curious about which things bring viral infections into a cell, protein or DNA. In 1952 they set out to find the answer to that question. Hershey and Chase grew colonies of bacteriophages, which are just viruses that infect bacteria. They then radioactively labelled sulfur and phosphorus, sulfur for protein and phosphorus for DNA, then put it into the bacteriophages. By only using a simple kitchen blender, Hershey and Chase separated the infected bacteria’s cytoplasm from it’s cell wall. They then analyzed both the cytoplasm and cell wall. They found that the DNA from the bacteriophages arrived in the bacteria, while the protein was still stuck in the cell wall. This experiment, named ‘The Waring Blender Experiment’ gave further proof that DNA is the genetics material for any organism.

Also in 1952, Rosalind Franklin found out the shape of DNA with her famous photograph ‘Photo 51’. Franklin was conducting diffraction studies of different DNA samples. The two samples she tested were called ‘A’ and ‘B’ forms. Franklin discovered that the shape of DNA is a helix by looking at ‘Photo 51’. This discovery ended up being necessary for Watson and Francis Crick to discover the double helix.

Only a year later, in 1953 James Watson and Francis Crick built on Rosalind Franklin’s discovery. From their own original model building, and crystallographic studies performed by Maurice Wilkins and Rosalind Franklin, Watson and Crick devised a theory that DNA is made up of two complementing chains composed of nucleotides wound around each other to make a double helix shape.

For many years, people thought that human cells each had 48 chromosomes. In 1956 this widely accepted number was proven to be wrong by Joe Hin Tjio. Tjio collected human cells that were undergoing the reproductive cycle and were currently in the metaphase. He then froze them using a drug by the name of colchicine. This allowed him to spread the chromosomes of the cells out, and count them all individually. Tjio discovered that there are 46 chromosomes in every human cell, not 48. Because of this discovery, a new field called human cytogenetics was started,

In 1957 Vernon Ingram closely studied normal and sickle cell hemoglobin, by using the sequencing method invented by Fred Sanger. The first step that Ingram took to study the hemoglobin was breaking them into smaller fragmented pieces using an enzyme called trypsin. It was in 1956 that Ingram learned that it was only of the many protein fragments that was different between the normal and sickle cell hemoglobin. Then in 1957, Ingram showed that the cause of the difference between the protein fragments was caused by only one amino acid being different in the two. This discovery is important because it is the first definite evidence that only one amino acid difference in only one protein can cause a serious disease.

It was the year 1958 that Arthur Kornberg identified the enzyme responsible for building DNA. The enzyme, DNA polymerase, was extracted from a sample of the E. Coli bacteria. This enzyme acted as a catalyst for the reformation of the double strands of DNA from a single strand.

Another exciting discovery was made in 1958 when Mahlon Hoagland and Paul Zamecnik found transfer RNA. Hoagland and Zamecnik were busy studying the synthesis of proteins cell-free extracts that came from the livers of rats. While studying that, they noticed that the RNA molecules, for only a short time, interacted with their radioactively labelled amino acids. Hoagland and Zamecnik made the guess that they discovered what Francis Crick predicted, the ‘adapter’. This adapter is found between the messenger RNA and the chain of protein. Soon after, this RNA was named transfer RNA, or tRNA for short.

Then in 1959 the cause of Down’s syndrome was discovered. Only recently prior to this discovery, was the correct number of chromosomes discovered, it being 46. Jerome Lejeune and Marthe Gautier discovered that children with Down’s syndrome had 47, only one extra one. The children all had a copy of the chromosome 21.


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