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During its life, an mRNA molecule may also be processed, edited, and transported prior to translation. Eukaryotic mRNA molecules often require extensive processing and transport, while prokaryotic mRNA molecules do not. A molecule of eukaryotic mRNA and the proteins surrounding it are together called a messenger RNP. [citation needed]
A typical operon. In genetics, an operon is a functioning unit of DNA containing a cluster of genes under the control of a single promoter. [1] The genes are transcribed together into an mRNA strand and either translated together in the cytoplasm, or undergo splicing to create monocistronic mRNAs that are translated separately, i.e. several strands of mRNA that each encode a single gene product.
Prokaryotic ribosomes begin translation of the mRNA transcript while DNA is still being transcribed. Thus translation and transcription are parallel processes. Bacterial mRNA are usually polycistronic and contain multiple ribosome binding sites. Translation initiation is the most highly regulated step of protein synthesis in prokaryotes.
Defining a Cistron as a segment of DNA coding for a polypeptide, the structural gene in a transcription unit could be said as monocistronic (mostly in eukaryotes) or polycistronic (mostly in bacteria and prokaryotes).
In the case of messenger RNA (mRNA) the RNA is an information carrier coding for the synthesis of one or more proteins. mRNA carrying a single protein sequence (common in eukaryotes) is monocistronic whilst mRNA carrying multiple protein sequences (common in prokaryotes) is known as polycistronic.
IRES sequences are often used in molecular biology to co-express multiple genes under the control of the same promoter, thereby mimicking a polycistronic mRNA. Within the past decades, IRES sequences have been used to develop hundreds of genetically modified rodent animal models. [12]
The overall organisation of prokaryotic genes is markedly different from that of the eukaryotes. The most obvious difference is that prokaryotic ORFs are often grouped into a polycistronic operon under the control of a shared set of regulatory sequences. These ORFs are all transcribed onto the same mRNA and so are co-regulated and often serve ...
Prokaryotic structural genes are transcribed into a polycistronic mRNA and subsequently translated. [1] In eukaryotes, structural genes are not sequentially placed. Each gene is instead composed of coding exons and interspersed non-coding introns. Regulatory sequences are typically found in non-coding regions upstream and downstream from the gene.