Transcription In Prokaryotes

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Synthesis, processing, and functionThe brief existence of an mRNA molecule begins with transcription and ultimately ends in degradation. 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 molecules do not. [edit] TranscriptionMain article: Transcription (genetics) Transcription is when DNA makes RNA. During transcription, RNA polymerase makes a copy of a gene from the DNA to mRNA as needed. This process is similar in eukaryotes and prokaryotes. One notable difference, however, is that prokaryotic RNA polymerase associates with mRNA-processing enzymes during transcription so that processing can proceed quickly after the start of transcription. The short-lived, unprocessed or partially processed, product is termed pre-mRNA; once completely processed, it is termed mature mRNA. [edit] Eukaryotic pre-mRNA processingMain article: Post-transcriptional modification Processing of mRNA differs greatly among eukaryotes, bacteria, and archea. Non-eukaryotic mRNA is, in essence, mature upon transcription and requires no processing, except in rare cases. Eukaryotic pre-mRNA, however, requires extensive processing. [edit] 5' cap additionMain article: 5' cap A 5' cap (also termed an RNA cap, an RNA 7-methylguanosine cap, or an RNA m7G cap) is a modified guanine nucleotide that has been added to the "front" or 5' end of a eukaryotic messenger RNA shortly after the start of transcription. The 5' cap consists of a terminal 7-methylguanosine residue that is linked through a 5'-5'-triphosphate bond to the first transcribed nucleotide. Its presence is critical for recognition by the ribosome and protection from RNases. Cap addition is coupled to transcription, and occurs co-transcriptionally, such that each influences the other.

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