 The ribosome is the macromolecular machine that directs the synthesis of proteins. The ribosome is large and even more complex than the minimal machinery required for RNA or DNA synthesis that is in replication of DNA or RNA. The machinery for polymerizing amino acids is composed of at least 3 RNA molecules and more than 50 different types of proteins. And overall these RNAs and proteins they make an overall molecular mass of more than 2.5 megadetons. Compared with the speed of DNA replication which is about 200 to 1000 nucleotides per second, translation takes place at a rate of only 2 to 20 amino acids per second. It means DNA synthesis or DNA replication is very fast as compared to translation or protein synthesis. In prokaryotes the transcription machinery and the translation machinery are located in the same compartment because you know in prokaryotes whole cell is the same compartment. There is no compartmentalization between nucleus and cytoplasm because nucleus is not present in the prokaryotic cells. So this all is present in the same compartment. Thus the ribosome can commence translation of the mRNA as it emerges from the RNA polymerase. So RNA transcription is taking place at one place in the cell. At the same place translation can be started. This situation allows the ribosome to proceed in tandem with the RNA polymerase as it elongates the transcript. So this means that as the RNA polymerase is being transcribed and the mRNA transcript elongates, the ribosome is also being followed and the ribosome is also being translated and the protein synthesis continues. Recall that the 5 prime end of an RNA is synthesized first and thus the ribosome which begins translation at the 5 prime end of the mRNA can start translating a nascent transcript as soon as it emerges from the RNA polymerase. So the first is that the 5 prime end of the RNA is synthesized from the 5 prime end of the RNA polymerase. This means that the 3 prime end of the RNA polymerase is now in the RNA polymerase and the 5 prime end of the RNA polymerase is now coming out. And the ribosome starts the translation from the 5 prime end of the RNA polymerase. So this means that the freshly prepared or nascent mRNA starts the translation as soon as it emerges from the RNA polymerase and the protein synthesis continues. So you can see in this figure that this is the RNA polymerase and this green is the mRNA transcript. So as soon as this is its 5 prime side, as soon as the RNA is formed, this ribosome is attached to it and the translation continues in this direction. And along with this direction, this polypeptide is formed. So in this way, the mRNA synthesis or protein synthesis may be coupled. Interestingly, there are several instances in which the coupling of transcription and translation is exploited during the regulation of gene expression. As soon as the gene expresses, it is regulated in such a way that the mRNA synthesis and the protein synthesis also start. Although slow relative to DNA synthesis in prokaryotes, the ribosome is capable of keeping up with the transcription machinery. As you have seen, the translation process is slow from RNA synthesis. But still, in prokaryotes, the translation machinery can keep up with it. The typical prokaryotic rate of translation of 20 amino acids per second corresponds to the translation of 60 nucleotides. Means 20 codons because there are three nucleotides in one codon. So these 20 codons are being translated in one second by mRNA. This is similar to the rate of 50 to 100 nucleotides per second synthesized by RNA polymerase. So 60 nucleotides are being used in one second for protein synthesis. So 50 to 100 nucleotides are being converted into RNA synthesis. This means that it corresponds. In contrast to the situation in prokaryotes, translation in eukaryotes is completely separate from transcription. Because in eukaryotes, mRNA synthesis is happening in nucleus and protein synthesis is happening in cytoplasm. So in eukaryotic cells, these two processes cannot be simultaneously run. These events occur in separate compartments of the cell. That is, transcription occurs in the nucleus whereas translation takes place in the cytoplasm. Perhaps due to lack of coupling to transcription, eukaryotic translation proceeds at the more layerly speed of 2 to 4 amino acids per second. That is, translation speed in eukaryotes is more slow compared to prokaryotes, in which 2 to 4 amino acids are formed in one second.