Academic journal article The American Biology Teacher

Three Lives in Biology

Academic journal article The American Biology Teacher

Three Lives in Biology

Article excerpt

Recently, I was searching for information on Bentley Glass, a distinguished geneticist and a founding member of the Biological Sciences Curriculum Study (BSCS), which celebrated its 50th anniversary in 2007. When I looked in a biographical index for January 2005, when Glass died, I discovered that two other important biologists also died the same month--Maclyn McCarty, one of the discovers of DNA as the genetic material, and Miriam Rothschild, a British entomologist and environmental activist. They were all over 90, with Glass dying one day short of his 99th birthday. I've decided to celebrate this coincidence by looking at the lives of all three biologists since each represents a different and significant tradition in biology. In addition, they were all just plain interesting people.

Maclyn McCarty

I'll begin with Maclyn McCarty (1911-2005) as the youngest of the group, dying at the age of 93. Along with Oswald Avery and Colin MacLeod, he published the 1944 paper which gave clear evidence that DNA was responsible for genetic change in pneumococcus. Until that time, biologists had not come to any conclusions about the identity of the genetic material, though many assumed it was protein. By this time it was clear that chromosomes were the site of the genes; many lines of evidence indicated this including the work of Thomas Hunt Morgan and his group on Drosophila genetics that linked mutations to chromosomal changes. However, chromosomes were known to contain both nucleic acid and protein, and because of protein's greater complexity, it seemed to be the more likely carrier of information, with nucleic acid merely providing structural support.

Oswald Avery was the senior microbiologist who, in 1928, began the hunt for the "transforming principle" which caused change in pneumococcus, the bacterium that is responsible for one of the scourges of the time, bacterial pneumonia. Specifically, he was studying how a noninfectious strain, without a polysaccharide coat, became a virulent strain with the coat: in other words, what contained the information to produce the polysaccharide. It had been known for some time that when virulent and nonvirulent strains were grown together, the nonvirulent strain sometimes became virulent, presumably because of the transfer of information from the virulent strain. But what was the chemical nature of this information? Avery began with a methodical approach attempting to separate out the chemical components of the bacterium and test each for its ability to "transform" the nonvirulent strain into a virulent one.

The polysaccharide itself was eliminated from consideration fairly early in the investigation, but then the going got difficult. Experimental results tended to be either inconclusive or contradictory. One time an experiment would work well and give clear results; the next time the same experiment was run, things would turn out differently. It was difficult to tell which set of evidence was significant. Only repeatedly getting the same results would lead the way, but this just didn't seem be possible to achieve.

There were several reasons for the inconsistency as McCarty recounts in his chronicle of this 16-year adventure, The Transforming Principle, published in 1985. He does a great job of describing what microbiological research was like in the years between the World Wars. Purification techniques were in their infancy, and researchers were only just becoming aware of how low levels of contamination could ruin experiments. One reason for the inconsistent results that Avery and his collaborators encountered was the presence of enzymes which destroyed nucleic acid. In some preparations these enzymes were sufficiently denatured to avoid problems, in others they were active enough to break down the transforming principle, yielding negative results.

In 1934, Colin MacLeod arrived in Avery's laboratory as a young doctor primed to do research on pneumococcus. …

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