<P> Transcription is when RNA is made from DNA . 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 eukaryotic 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 precursor mRNA, or pre-mRNA; once completely processed, it is termed mature mRNA . </P> <P> 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 . </P> <P> A 5' cap (also termed an RNA cap, an RNA 7 - methylguanosine cap, or an RNA m G 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 . </P> <P> Cap addition is coupled to transcription, and occurs co-transcriptionally, such that each influences the other . Shortly after the start of transcription, the 5' end of the mRNA being synthesized is bound by a cap - synthesizing complex associated with RNA polymerase . This enzymatic complex catalyzes the chemical reactions that are required for mRNA capping . Synthesis proceeds as a multi-step biochemical reaction . </P>

Where is the messenger rna synthesized in a cell