The large and small subunits of eukaryotic cells are formed in the nucleus. In nucleoli, rDNA transcribes 45S rRNA, which is the precursor molecule of rRNA. Combined with protein transported by cytoplasm, it was processed and cut into 28S, 18S and 5.8S rRNA by enzyme, while 5S rRNA synthesized 28S, 5.8S and 5S rRNA outside nucleolus and combined with protein to form RNP molecular clusters. It is the precursor of large subunit and dispersed in nucleolar granule area. After processing, 18S rRNA entered the cytoplasm through the nuclear pore and became a large subunit, and also combined with protein, and entered the cytoplasm through the nuclear pore and became a small subunit. The large and small subunits can be dissociated in cytoplasm and in >: when 0.00 1M Mg exists, but a single ribosome is synthesized completely, it has a synthetic function. When Mg4
Prokaryotic cells have a small ribosome with a sedimentation coefficient of 70S and a relative molecular weight of 2.5x 103 kDa, which consists of 50S and 30S subunits. However, eukaryotic cells have larger ribosomes, with a sedimentation coefficient of 80S and a relative molecular weight of 3.9 ~ 4.5x 103kda, consisting of 60S and 40S subunits. Escherichia coli is a typical prokaryote, and its ribosome consists of 50S large subunit and 30S small subunit. In the whole ribosome, rRNA accounts for about 2/3, and protein is about 1/3. The large subunit of 50S contains 34 different protein and two RNA molecules, the sedimentation coefficient of relatively large molecular weight rRNA is 23S, and the sedimentation coefficient of relatively small molecular weight rRNA is 5S. The 30S subunit contains 2 1 protein and 16S rRNA molecules.