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Transcription and translation are processes for protein synthesis in both Eukaryotic and Prokaryotic cells. During transcription, RNA (Ribose Nucleic Acid) is synthesized from DNA (De-oxy Ribose Nucleic Acid), and during translation, protein or polypeptides are synthesized from RNA (It is mRNA or messenger RNA actually, which is nothing but the RNA containing genetic information of the cell as compared to the tRNA and the rRNA).
There are similarities between the two processes. For example, the end result of transcription and translation in both kinds of cells remains the same, i.e. synthesis of proteins, both Eukaryotes and Prokaryotes require RNA Polymerase to act on the DNA for transcription, and transcription initiation happens at the “promoter”, etc. However, we are concerned mainly with the differences. Both transcription and translation are much more complex processes in Eukaryotes than in Prokaryotes (Well, the structure and functional capacities of Eukaryotic cells are much more complex and rich in almost every other aspect as compared to Prokaryotic cells).
In Eukaryotic cells, transcription and transcription occur in separate compartments of the cell. Transcription takes place inside a membrane-bound compartment, the nucleus. At first, a pre-mRNA is synthesized by the action of RNA Polymerase. This pre-mRNA, then, gets converted into mRNA (we call it “mature” mRNA) that is transferred outside the nucleus to the ribosomes of endoplasmic reticulum where it is translated into proteins.
We know that, unlike the Eukaryotic cells, the DNA (or nucleic material) in Prokaryotic cells is not enclosed by a membrane and is easily available for transcription by the RNA Polymerase. Here, the mRNA starts getting translated into proteins at the same time while it is getting synthesized from DNA. Hence, unlike Eukaryotic cells, transcription and translation are coupled together in Prokaryotes and there is essentially no time delay between them. Also, both of these processes take place in the same place, i.e. cell cytoplasm.
There are 3 kinds of RNA Polymerases (RNA Polymerase I, RNA Polymerase II and RNA Polymerase III) that act on DNA in Eukaryotes to synthesize mRNA. In contrast, only one type of RNA Polymerase acts on the DNA in Prokaryotes.
The mRNA, in nascent stage, is extensively modified by the addition of a cap at 5’ end and a poly tail at 3’ end and introns are sliced. But it doesn’t undergo any such modification and slicing in prokaryotes.
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