Fred Griffith Controversy

How do we know that genes are made of DNA? In the 1920s, scientists agreed that genes are located on chromosomes, and they already knew that DNA and proteins make up chromosomes. They assumed that genes were made of proteins because DNA is chemically simple and proteins are not, but this was proven to be wrong. In the late 1920s, a great discovery was made by Fred Griffith while studying Streptococcus pneumonia (pneumococcus). He found that pneumococci come in a pathogenic form and a harmless form. During his research, he injected many different preparations of these bacteria into mice. He heat-killed pathogenic pneumococci and discovered that it was no longer lethal when injected. Griffith was surprised to find that when both heat-killed pathogenic and harmless bacteria were injected into the mice together, the mice were killed and their blood stream was full of live pathogenic bacteria. By growing these “transformed” bacteria in cultures, he found that the change was permanent and the bacteria stayed pathogenic. He was unable to determine what material turned the harmless bacteria into pathogenic bacteria or how the change was passed on. …show more content…
After 15 years, Avery and his colleagues, Colin MacLeod and Maclyn McCarty, purified the “transforming principle” and demonstrated that DNA was the active ingredient. A series of chemical tests were done that showed that the material passed on had all the chemical properties of DNA. Enzymes that destroy proteins and RNA had no effect on the transformation of harmless bacteria to pathogenic bacteria, but enzymes that destroy DNA inactivated the transformation. A paper stating the findings of Avery and his team was released in 1944, but little attention was drawn from