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In Eukaryotes, however, this process primarily takes place in the nucleolus and is initiated by the synthesis of pre-RNA. This requires the presence of all three RNA polymerases. In fact, the transcription of pre-RNA by RNA polymerase I accounts for about 60% of cell's total cellular RNA transcription. [19]
In prokaryotes, this process takes place in the cytoplasm with the transcription of many ribosome gene operons. In eukaryotes, it takes place both in the cytoplasm and in the nucleolus . It involves the coordinated function of over 200 proteins in the synthesis and processing of the three prokaryotic or four eukaryotic rRNAs , as well as ...
The transcription of rRNA genes takes place in a specialised structure of the nucleus called the nucleolus, [5] where the transcribed rRNAs are combined with proteins to form ribosomes. [ 6 ] RNA polymerase II (Pol II) is responsible for the transcription of all mRNAs, some snRNAs, siRNAs, and all miRNAs.
In eukaryotes, the process takes place both in the cell cytoplasm and in the nucleolus, which is a region within the cell nucleus. The assembly process involves the coordinated function of over 200 proteins in the synthesis and processing of the four rRNAs, as well as assembly of those rRNAs with the ribosomal proteins. [64]
Eukaryotic ribosomes contain four different rRNA molecules: 18S, 5.8S, 28S and 5S rRNA. Three of the rRNA molecules are synthesized in the nucleolus, and one is synthesized elsewhere. In the cytoplasm, ribosomal RNA and protein combine to form a nucleoprotein called a ribosome. The ribosome binds mRNA and carries out protein synthesis.
Overview of eukaryotic messenger RNA (mRNA) translation Translation of mRNA and ribosomal protein synthesis Initiation and elongation stages of translation involving RNA nucleobases, the ribosome, transfer RNA, and amino acids The three phases of translation: (1) in initiation, the small ribosomal subunit binds to the RNA strand and the initiator tRNA–amino acid complex binds to the start ...
Ribonucleoprotein (RNP) particles called ribosomes are the 'factories' where translation takes place in the cell. The ribosome consists of more than 60% ribosomal RNA; these are made up of 3 ncRNAs in prokaryotes and 4 ncRNAs in eukaryotes. Ribosomal RNAs catalyse the translation of nucleotide sequences to protein.
For example, some prokaryotic bacterial mRNAs serve as templates for synthesis of proteins at the same time they are being produced via transcription. Alternatively, pre-mRNA of eukaryotic cells undergo a wide range of modifications prior to their transport from the nucleus to cytoplasm where their mature forms are translated. [ 9 ]