Question

What was the significance of the 1944 Avery-MacLeod-McCarty experiment? How are the discoveries of that experiment a significant contribution to the field of biotechnology?

Answer 1

Significance of the 1944 Avery-MacLeod-McCarty experiment:
Oswald Avery, Colin MacLeod, and Maclyn McCarty showed that non protein DNA can transform the properties of cells. It can also clarify the chemical nature of genes.
Avery, MacLeod and McCarty identified DNA as the "transforming principle" when he was studying Streptococcus pneumoniae, bacteria that can cause pneumonia. The bacteriologists were interested in the difference between two strains of Streptococci. Frederick Griffith had identified that in 1923: one, the S or the smooth strain which has a polysaccharide coat and produces smooth, shiny colonies on a lab plate. And the other, the R or the rough strain, lacks the coat and produces colonies that look rough and irregular. The relatively harmless R strain lacks an enzyme needed to make the capsule found in the virulent S strain.
Griffith had discovered that he could convert the R strain into the virulent S strain. After simultaneously injecting mice with R strain cells and then with heat-killed cells of the S strain, the mice developed pneumonia and then died. Griffith found live bacteria of the deadly S type in their blood. The S strain extract somehow had "transformed" the R strain bacteria to S form. Avery and members of his lab studied transformation in fits and starts over the next 15 years. In the early 1940s, they began a concerted effort to purify the "transforming principle" and understand its chemical nature.
Bacteriologists suspected the transforming factor was some kind of protein. The transforming principle could be precipitated with alcohol. It showed that it was not a carbohydrate like the polysaccharide coat itself. But Avery and McCarty observed that proteases - enzymes that degrade proteins - did not destroy the transforming principle. Neither did lipases - enzymes that digest lipids. They found that the transforming substance was rich in nucleic acids, but ribonuclease that digests RNA, did not inactivate the substance. They also found that the transforming principle had a high molecular weight. They had isolated DNA. This was the agent that could produce an enduring, heritable change in an organism.
Until then, biochemists had assumed that deoxyribonucleic acid was a relatively unimportant, structural chemical in chromosomes and that proteins, with their greater chemical complexity, transmitted genetic traits.

Contribution to the field of biotechnology:
The Avery, MacLeod anf McCarty's experiment was an experimental demonstration. It was reported in 1944 by Oswald Avery, Colin MacLeod, and Maclyn McCarty, that DNA is the substance that causes bacterial transformation. It happened in an era when it had been widely believed that it was proteins that served the function of carrying genetic information. It was the culmination of research in the 1930s and early 20th century at the Rockefeller Institute for Medical Research to purify and characterize the "transforming principle". It was responsible for the transformation phenomenon first described in Griffith's experiment of 1928. It killed Streptococcus pneumoniae of the virulentstrain type III-S, when it was injected along with living but non-virulent type II-R pneumococci. This resulted in a deadly infection of type III-S pneumococci. In their paper "Studies on the Chemical Nature of the Substance Inducing Transformation of Pneumococcal Types: Induction of Transformation by a Desoxyribonucleic Acid Fraction that is Isolated from Pneumococcus Type III", published in the February 1944 issue of the Journal of Experimental Medicine. Avery and his colleagues suggest that DNA, rather than protein as widely believed at the time, may be the hereditary material of bacteria, and could be analogous to genes and viruses in higher organisms.
With the development of serological typing, medical researchers were able to sort bacteria into different strains, or types. When a person or test animal is inoculated with a particular type, an immune response ensues, generating antibodies that react specifically with antigens on the bacteria. Blood serum containing the antibodies can then be extracted and applied to cultured bacteria. The antibodies will react with other bacteria of the same type as the original inoculation. Fred Neufeld, a German bacteriologist, had discovered the pneumococcal types and serological typing; until Frederick Griffith's studies bacteriologists believed that the types were fixed and unchangeable from one generation to the next.
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