Translation

ID #2354

During cotranscriptional translation are all RNA polymerases making the same mRNA transcript from the template DNA and all ribosomes making the same amino acid chain (protein) from the mRNA transcript? Or not same protein because of polycistronic property, but are the products of transcription and translation the same for every single E coli RNA polymerase and every ribosome?


Cotranscriptional translation occurs in bacteria and archae, but not eukaryotes. Prokaryotic genes can be monocistronic or polycistronic. A monocistronic gene is a single gene controlled by a single promoter. A group of genes (that are usually producing related but not identical proteins) are polycistronic if the transcription of the group of genes is controlled by one promoter. 
The monocistronic case is simpler because as you said initially all RNA polymerases are making the same RNA transcript from the template DNA and all ribosomes are making the same amino acid chain from the RNA transcript if the gene is monocistronic. 
For the polycistronic genes, RNA polymerases are making the same RNA transcript which contains the message for more than one gene. But in this case, the ribosomes would be able to make different protein products from one RNA (see lecture 19 slide 14 for how they do that). 
The image of cotranscriptional translation shown in one of the slides from lecture 20 could be indicating either monocistronic or polycistronic because you are not told specifically how many genes are present in the DNA or how many corresponding shine delgarno (SD) sequences there are in the RNA. 

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