Word: rna
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Dates: during 1960-1969
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...Cornell, Holley studied both the genetic code and its function in building proteins by analyzing "transfer RNA," a form of ribonucleic acid. RNA collects amino acids floating in the cell and, like a tug towing a barge, pulls them to an assembly site where, in the sequence dictated by the master DNA molecule, they are combined into the appropriate protein. Holley worked out the complete structure of a transfer RNA molecule, demonstrating how it attaches to a particular amino acid and brings it to the growing protein chain at the proper time and place...
Kafatos points out that even if the nucleus of a fertilized egg is removed, the egg can still give rise to a very young embyro. This demonstrates that stable messenger RNA for making an embryo had been stored in the egg's cytoplasm. Storage may well be the level where the critical choice might reside in the cells of higher organisms. This is not the case for very simple cells like bacteria, where the genetic information is transcribed into RNA and immediately translated into protein. Kafatos explained that, due to the great instability of the bacterial world, bacteria...
...example of a highly differentiated organ. About 70 per cent of the protein made by this gland is one enzyme, "cocoonaise." The rest is proteins needed for cell maintenance and growth. The message for making the differentiation - specific protein is extra stable. That is, each molecule of cocoonaise - messenger RNA remains active in the cytoplasm for at least two days. By contrast, the rest of the cell's messengers only survive for a few hours. Presumably, their decay introduces flexibility in the non-specialized functions of the cell...
...stopped the synthesis of all RNA by treating the cells with the specific antibiotic Actinomycin D, which is, incidentally, used to stop the growth of cancer cells. From then on, all protein synthesis depended on pre-existing messengers. He detected new protein molecules by exposing the cells to radioactive amino acids, which are incorporated into any protein the cell synthesizes. Kafatos has made thin sections of the cell and covered them with a thin photographic film. The radioactivity behaves like light and activated the film. His process is called autoradiography. He could then develop the film, count the activated silver...
After investigating the stability of RNA, Kafatos turned to possible mechanisms for transporting the RNA to the cytoplasm. Extending his Widener metaphor, he said the first possibility is similar to a Cliffie going into the stacks to obtain the book herself while the second is like her using the library's call system, having the book delivered up to the reading room. In the first possibility, the actual users of the genetic information, the ribosomes, or protein-synthesizing particles, may carry messenger RNA from the nucleus to the cytoplasm, the cite of protein synthesis. Second, there may exist a distinct...