Instead of a single polymerase comprising five subunits, the eukaryotes have three polymerases that are each made up of 10 subunits or more. The features of eukaryotic mRNA synthesis are markedly more complex those of prokaryotes. Unlike the prokaryotic polymerase that can bind to a DNA template on its own, eukaryotes require several other proteins, called transcription factors, to first bind to the promoter region and then help recruit the appropriate polymerase. Read on to learn the role of RNA polymerases at each stage of transcription. This section will expand upon the specific role of RNA polymerases during transcription. (After this point, it discusses translation, which we’ll discuss in the next outcome.) This video provides a review of these steps. The mRNA strand is complete, and it detaches from DNA. Termination is the ending of transcription, and occurs when RNA polymerase crosses a stop (termination) sequence in the gene. During this process, an adenine (A) in the DNA binds to an uracil (U) in the RNA. There is a brief time during this process when the newly formed RNA is bound to the unwound DNA. RNA polymerase reads the unwound DNA strand and builds the mRNA molecule, using complementary base pairs. Step 2: ElongationĮlongation is the addition of nucleotides to the mRNA strand. The enzyme is now ready to make a strand of mRNA with a complementary sequence of bases. This signals the DNA to unwind so the enzyme can ‘‘read’’ the bases in one of the DNA strands. ![]() ![]() It occurs when the enzyme RNA polymerase binds to a region of a gene called the promoter. Initiation is the beginning of transcription. Transcription occurs in the three steps-initiation, elongation, and termination-all shown here.
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