George Palade Biography (1912-)

cell biologist

George Emil Palade was born in 1912, in northeastern Romania. One of three children, Palade came from a professional family and earned his medical degreefrom the University of Bucharest in 1940. In 1941, he married Irina Malaxa; they eventually had two children together.

In 1945, after being discharged from the army, Palade obtained a research position at New York University. While there he met the eminent cell biologist Albert Claude, who had pioneered both the use of the electron microscope in cell study and techniques of cell fractionation (the separation of the constituent parts of cells by centrifugal action). The older scientist invited Paladeto join the staff at the Rockefeller Institute (now Rockefeller University),and in 1946 Palade accepted a two-year fellowship as visiting investigator.Political instability in Romania caused Palade to stay in the United States permanently. He became a U.S. citizen in 1952 and a full professor of cytologyat Rockefeller in 1958.

At the Rockefeller Institute, Palade and his collaborators reported groundbreaking descriptions of the fine appearance of the cell and of its biochemicalfunction. Concentrating on the cytoplasm--the living material in the cell outside the nucleus--Palade was first attracted to larger organelles (bodies ofdefinite structure and function in the cytoplasm) which Claude had earlier called "secretory granules." Palade showed that these tiny sausage-shaped structures, mitochondria, are the site where energy for the cell is generated. Animal cells typically contain a thousand such mitochondria, each creating adenosine triphosphate (ATP), a high-energy phosphate molecule--through enzymic (enzyme-catalyzed) oxidation or breakdown of fat and sugar. The ATP is then released into the cytoplasm where it powers energy-requiring mechanisms such asnerve impulse conduction, muscle contraction, or protein synthesis.

Using the high-power electron microscope (a device that utilizes electrons instead of light to form images of minute objects), Palade next revealed a delicate tracery, subsequently termed the endoplasmic reticulum. The endoplasmicreticulum is a series of double-layered membranes present throughout all cells except mature erythrocytes, or red blood cells. Its function is the formation and transport of fats and proteins. By far Palade's most significant workwas with so-called microsomes, small bodies in the cytoplasm that Claude hadearlier identified and shown to have a relatively high ribonucleic acid (RNA)content. RNA is the genetic messenger in protein synthesis. Palade observedthese microsomes both as free bodies within the cytoplasm, and attached to the endoplasmic reticulum. In 1956, using a high-speed centrifuge, Palade and his colleague Philip Siekevitz were able to isolate microsomes and observe them under the electron microscope. They discovered that these microsomes were made of equal parts of RNA and protein.

Palade assumed that these RNA-rich microsomes were in fact the factories producing protein to sustain not only the cell but the entire organism. The microsome was renamed the ribosome, and Palade and his team went to work to investigate the pathway of protein synthesis in the cell. Palade and Siekevitz began a series of experiments on ribosomes of the liver and pancreas, employing autoradiographic tracing, a sophisticated process similar to X-ray photographyin which a picture is produced by radiation. Investigating in particular exocrine cells (those that secrete externally) of the guinea pig pancreas, the team was able, by 1960, to show that ribosomes do in fact synthesize proteinsthat are then transported through the endoplasmic reticulum. Further researchelucidated the function of the larger ribosomes attached to the endoplasmicreticulum, establishing them as the site where amino acids assemble into polypeptides (chains of amino acids).

Having completed his work on protein synthesis, Palade turned his attention to cellular transport--the means by which substances move through cell membranes. Working with Marilyn G. Farquhar, Palade demonstrated by electron micrography (images formed using an electron microscope) that molecules and ions were engorged by sacs or vesicles that move to the surface from within the cell.These vesicles actually merge with the outer membrane for a time, and then swallow up and bring the substances inside the cell. This vesicular model wasin distinct contrast to the then current pore model whereby it was thought that molecules simply entered the cell through pores in the membrane.

Palade's later work at Yale University has been an attempt to establish linksbetween defects in cellular protein production and various illnesses. In 1974 Palade shared the Nobel Prize in Physiology or Medicine with his former mentor, Albert Claude, and with Christian R. de Duvé, for their descriptions of the detailed microscopic structure and functions of the cell. In 1990, Palade left Yale to become the dean for scientific affairs at the University of California, San Diego.

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