166 Cell Structure
what each isolated layer was and to learn how to successfully isolate the tumor agent from
the rest of the cell. Claude’s chemical analysis showed this agent to be a ribonucleic acid
(RNA), a known constituent of viruses. This was the first evidence that cancer was caused
by a virus.
Claude decided to continue using cell fractionation to study healthy cells. Working
full-time in his laboratory over the next six years using a centrifuge and a high-powered microscope, Claude was able to isolate and describe the cell nucleus (the structure that houses
the chromosomes), organelles (specialized microscopic structures within a cell that act like
organs), mitochondria (tiny rod-shaped granules where respiration and energy production
actually happen), and ribosomes (the sites within cells where proteins are formed).
Claude was mapping a new world that had only been guessed at before. Still, his view
was limited by the power of his microscope. In 1942 the Rockefeller Institute was able to
borrow the only electron microscope in New York, used by physicists attempting to probe
inside an atom. This scope was capable of magnifying objects one million times their
original size.
However, the scope also bombarded a sample with a powerful beam of electrons in order to create an image. Such an electron stream destroyed fragile living tissue. Claude spent
18 months developing successful methods to prepare and protect cell samples to withstand
the electron microscope. By mid-1943 Claude had obtained the first actual images of the internal structure of a cell, images previously unthinkable. In 1945 Claude published a catalog of dozens of new cell structures and functions never before identified.
The names of the scientists who broke the barrier of an atom