. The biosynthesis of proteins. Proteins -- Synthesis. CHAPTER II The Sites of Protein Formation within the Living Cell A. EARLY CYTOCHEMICAL DATA The first data on the sites of protein synthesis in the cell emerged from cytochemical studies by Brachet and by Caspersson. Brachet (1933) had observed that the variations of DNA content during the development of the sea urchin egg do not parallel the changes of 'nucleic phosphorus'. This called his attention upon the possible existence of other nucleic acids beside DNA in this material. But at the time, there was no method available for detecting
. The biosynthesis of proteins. Proteins -- Synthesis. CHAPTER II The Sites of Protein Formation within the Living Cell A. EARLY CYTOCHEMICAL DATA The first data on the sites of protein synthesis in the cell emerged from cytochemical studies by Brachet and by Caspersson. Brachet (1933) had observed that the variations of DNA content during the development of the sea urchin egg do not parallel the changes of 'nucleic phosphorus'. This called his attention upon the possible existence of other nucleic acids beside DNA in this material. But at the time, there was no method available for detecting or for determining ribosenucleic acids. Plant nucleic acid, as RNA was then usually named, was regarded as a biochemical curiosity, so rich in phosphate that it was probably a phosphate storage form, which occurs in wheat germ, in yeast, and curiously enough also in pancreas. A few years later, the purification and isolation of pancreatic ribonuclease (Kunitz, 1940) provided a means of destroying RNA specifically. Making use of this new tool, Brachet tried to see which structures or regions of animal cells would be affected by ribonuclease. Brachet (1941) established that the basophilic substance of the cytoplasm of animal tissues is speci- fically removed by pancreatic ribonuclease. The substance responsible for cytoplasmic basophilia was thus clearly identified as RNA, and at the same time a very simple method for the detection and localization of RNA in tissue sections was introduced. A screening of animal tissues by this technique demonstrated the presence of RNA in all types of cells and showed that RNA is responsible for the basophilia of ergastoplasm and nucleoli. During cell division, RNA is also found in chromosomes and in the spindle. But by far the largest amount of RNA is in the cytoplasm. Caspersson, on the other hand, had developed a microspectrophoto- meter with which he was able to measure light transmission at selected wave lengths in the ultraviolet on small r
Size: 1501px × 1665px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookcollectionameri, bookcollectionbiodiversity
