Johann Friedrich Miescher | DISCOVERY OF DNA | Dr. MALIK

 Johann Friedrich Miescher

Johann Friedrich Miescher

Friedrich Miescher was an intelligent person but he had problems with hearing. He completed his graduation from medical school in 1868 and after his graduation, he was more interested in the research field and did not want to be a practicing doctor because of his hearing problems.

In the winter of 1869, this young doctor Friedrich Miescher worked in the laboratory of the University of Tübingen.

He performed experiments on the chemical composition of leukocytes that led to the discovery of DNA.

He discovered DNA from the waste of bandages with blood.

Experiment.

• Friedrich Miescher wanted to explore the nucleus of the living cell.
• He wanted to study the material present in the cell of the nucleus. 
• For this purpose, he take some bandages, which were waste material, and had blood on them.

So, the question is, what he was going to do with these bandages?

The answer is that he wanted the samples of white blood cells because white blood cells have large size of nuclei with them.

• He washed these bandages with water and made a dilute solution of water plus blood cells.
• Now the water contains blood cells, especially white blood cells.
• Here the main problem begins, which is the separation of the nucleus from the cell.
• He has done many experiments for this separation and finally, he got to succeed.

Now, how does he separate the nucleus from the cell?

This was done in two steps.

1. Firstly, He washed the blood solution with alcohol. Alcohol removes the lipid bilayer from the cell.
2. Then he used pepsin, which he obtained from the stomach of a pig. This pepsin removed all the materials from the cell except the nucleus.

In this way, he got the nucleus from the living cell.

Now, he wanted to explore the nucleus.

1. For this purpose, he used base wash, which ruptures the nuclear membrane.
2. And In the last, he used some acid wash. After this acid wash, he got a white precipitate.

Friedrich Miescher thought that it was a protein because most cell is made up of protein but he was wrong. It was not protein, it was DNA.

Now, how did Friedrich Miescher confirm that the white precipitate material is not protein?

1. He used protease enzyme. And when he observed some resistance from the white precipitate, he confirmed that it was not a protein.
2. However, he observed phosphorus in the white precipitate material which also indicates that the white material is not a protein.

He called this white precipitate material, the nuclein, which we called deoxyribonucleic acid or DNA.

Now, how did he observe the phosphorus in the nuclein?

He observed phosphorous in nuclein through the process of elementary analysis. He separated all the elements and observed the elements like:

1. Hydrogen
2. Oxygen
3. Nitrogen
4. Carbon
5. And phosphorous.

 

Conclusion.

• Friedrich Miescher said that nuclein had an important role in cell division. 
• He suggested that with the increases in the size of nuclear substances, cell division takes place.
• Miescher even speculated that it might have a role in the transmission of hereditary traits, but this idea was rejected.

He published his work in 1871.

Friedrich Meischer discovered DNA and said that it was a hereditary material and important in inheritance but nobody was interested in his work and he died in 1895 with Tuberculosis ( a disease).