History of DNA Discovery (2): Friedrich Miescher, “Nuclein”

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The Swiss physician and biologist Friedrich Miescher, who isolated nuclear extracts and named them "nuclein", marked the first step on the path of DNA and the genetic material exploration in human history.

Early Education

Friedrich Miescher was born into a family with a strong academic background in Basel, Switzerland, on August 13, 1844. His father was a professor of anatomy at the University of Basel, and his uncle, Wilhelm His, was an embryologist.

Friedrich Miescher was shy and introverted in childhood but was considered very intelligent and performed well in school. His family background prompted him to choose a career in medicine,and he enrolled at the University of Basel to study medicine in 1861. He was also highly interested in biochemistry. His first mentor was the renowned organic chemist Adolf Strecker, the first person to synthetically create an amino acid, and the Strecker Synthesis is named after him. He conducted organic chemistry research in Adolf Strecker's laboratory in 1865. The typhoid fever interrupted his studies for nearly a year during this period. Despite this setback, he still obtained his doctorate degree from the University of Basel in 1868.

Miescher was more interested in the various chemical components within cells than in the synthesis of organic compounds. After earning his doctorate, he worked as an assistant in the laboratory of Hoppe-Seyler, one of the most distinguished biochemists of that era.

How did Friedrich Miescher discovery "nuclein" (crude extract of DNA)?

While scientists were still debating the concept of "cell", Hoppe Seyler's laboratory was already isolating the components that make up cells. The primary task assigned to him by Hoppe Seyler was studying the biochemical components of lymphocytes. However, Miescher found it difficult to extract lymphocytes with sufficient purity from the lymph glands. Therefore, he focused to the biochemical components of white blood cells. A nearby clinic provided him with discarded bandages where the fresh pus was an ideal source of white blood cells.

Miescher washed the white blood cells off the bandages with various salt solutions and then treated them with chemical reagents. It was a highly tedious task to classify the lipids and proteins in extracts by microscope. One day, he discovered an extract that would precipitate in acid and redissolve in alkali. The precipitate was insoluble in water, acetic acid, dilute hydrochloric acid, or salt solution, unlike any known protein. Undoubtedly, Friedrich Miescher had obtained the first crude extract of DNA in human history.

Friedrich Miescher suspected this substance originated from the cell nucleus because almost everything from the cytoplasm had been removed by the hydrochloric acid. He conducted the experiment more meticulously. He selected bandages that had non-degraded cells under the microscope. He tried various salt solutions and found that cells washed by sodium sulfate were not damaged. The cell suspension was filtered and stand 1 or 2 hours for sedimentation. Finally, he re-examined the sediment by microscope to ensure nearly all the cells were intact.

The next step was to extract the substance inside the cell nucleus. This step had to be conducted in winter to ensure the DNA would not degrade. Miescher treated these cells with a thousand times diluted hydrochloric acid for several weeks. The lipids and proteins in the cell membrane was destroyed by acid and substance in nucleus was released into the solution. The cytoplasm was stained by iodine to detect whether they had been completely removed. Finally, he vigorously shook the cell nuclear substance with water and ether to remove lipids and other hydrophobic molecules. The precipitate in the aqueous phase was the mysterious substance he sought. Since it came from the cell nucleus, Friedrich Miescher named it "nuclein". The "nuclein" acquired by this method was too little for chemical analysis, so he improved the extraction technique. The pus was washed by ethanol, then the cytoplasm and proteins was digested by pepsin extracted from pig stomachs. Remove lipids by ether was still necessary.

The properties of“nuclein”

Having obtained sufficient and adequately pure "nuclein", Friedrich Miescher tested its properties. He found that "nuclein" would swell and gradually disappear in alkaline solution. If acid was added, the flocculent "nuclein" would reappear. The "nuclein" did not coagulate like protein but directly disappeared in boiling water (DNA was hydrolyzed in boiling water). Friedrich Miescher also found that "nuclein" contained not only the carbon, nitrogen, hydrogen, oxygen and sulfur that were common in protein, he was also surprised that it contained a large amount of phosphorus. Subsequent burning tests of "nuclein" confirmed that phosphorus existed as an organic rather than an inorganic substance. Although these properties were completely different from proteins, "nuclein" could also be dyed yellow by nitric acid, which was similar to proteins. We now know that the "nuclein" extracted by him was contaminated with proteins because of the poor equipment at that time.

The "nuclein" was also found in the kidney, liver, testes and yeast cells. He believed that it will prove to be as important as proteins. Hoppe Seyler was skeptical of Miescher's conclusions, so he temporarily confiscated the paper. He repeated the experiment with yeast and came to the same conclusions. The paper about "nuclein" in pus cells was not published until 1871.

Friedrich Miescher used salmon sperm to study "nuclein" and extracted protamine.

Friedrich Miescher had served as a biological professor at Basel University since 1872. The swarms of salmon swam upstream from the North Sea to the upper reaches of Rhine River during the breeding season. He often fishes near the university in the early morning and brings fishes to the lab.

Most of the space in the sperm head was occupied by the nucleus, while the proteins responsible for movement were concentrated in the tail. Therefore, sperm was the most suitable cell for studying "nuclein". The analysis of sperm extract showed that "nuclein" did not contain sulfur. Moreover, he accurately calculated the content of phosphorus. It contained 22.5% P₂O₅, a figure very close to the actual ratio of 22.9%. These phosphorus were all present in "nuclein" in the form of phosphoric acid.

During the extraction of "nuclein", he also discovered an alkaline protein that was closely bound to "nuclein", which he called protamine. However, he did not delve deeply into the property of protamine.

Friedrich Miescher's interest in "nuclein" began to wane after 1875. He devoted more energy and time to fertilization and teaching. Giving classes to students and being perfectionist about work made him take less and less time off, even spending most of his vacations in the lab. He became exhausted and weak. He infected tuberculosis in the early 1890s and died in 1895.

The Achievements of Friedrich Miescher

Superstar scientists in history who have withstood attacks from the mainstream and pioneered new fields to guide the path of science. Friedrich Miescher also seemed to have the opportunity to become a superstar in the scientific community during his lifetime. However, nearly everyone resisted his new ideas. They thought "nuclein" was just a protein contaminated during the extraction process, and even launched merciless criticism against Friedrich Miescher. His achievement as the first discoverer of DNA was not re-established until it was discovered that DNA was the controller of inherited traits. It is fair to say that Friedrich Miescher died almost with regret and confusion, even though his achievements surpassed most of his contemporaries in biology.

Frequently Asked Questions

Why was "nuclein" extracted during the cold winter?

If the temperature is not low enough, the proliferating bacteria would degrade "nuclein" to give an inaccurate result. In modern biological laboratories, experimental materials are preserved by refrigerators that had not been invented in the 19th century. Friedrich Miescher had to conduct experiments on cold winter mornings with all the opening windows to prevent degradation. Working for long periods in low temperatures damaged his health.

Why did Friedrich Miescher become the first person to discover "nuclein" (DNA)?

His success in isolating DNA was largely due to the choice of cells. White blood cells and sperm do not embed in tissues or extracellular matrices, and can be easily purified. Moreover, their nucleus were larger than the cytoplasm, especially in sperm, facilitating an enrichment of nuclear components in purification protocols.

What properties of "nuclein" (DNA) were discovered by Friedrich Miescher?

He found that "nuclein" (DNA) would decompose in boiling water. It dissolves in alkaline solutions and is insoluble in acidic solutions, water, and organic solvents. It does not contain sulfur but has a considerable amount of phosphorus.

What function of "nuclein" did Friedrich Miescher discover?

We now know that "nuclein" is the DNA that stores hereditary information. However, the knowledge about DNA was virtually nonexistent at that time, even Miescher himself was uncertain about the "nuclein" function. He hypothesized that "nuclein" might serve as a storage for phosphorus to aid the synthesis of other molecules, but experiment seldom supported this theory. He took a different approach and obtain the ratio of "nuclein" to protein in different states of cell. An notable increase in "nuclein" was observed preceding cell division, expecially in tumors. "Nuclein" was also observed in liver, kidney, yeast, red blood cells and eggs. He realize that ubiquitous "nuclein" was no less important to life than proteins. Friedrich Miescher was close to a final answer, but he did not take the decisive step. He refused to recognize "nuclein" as genetic material and followed the prevailing view that proteins stored genetic information.

Anec  > Biology > Genetic material