mRNA (messenger RNA) is synthesized through a process called transcription, which occurs in the nucleus of eukaryotic cells. Here's a simplified overview of how mRNA is made:
- Initiation: Transcription begins when RNA polymerase, an enzyme, binds to a specific region of DNA called the promoter. This marks the start site for transcription.
- Elongation: RNA polymerase unwinds the DNA double helix, exposing the template strand. It then adds complementary RNA nucleotides (adenine, cytosine, guanine, and uracil) to the growing mRNA strand, following the base pairing rules (A-U, C-G). As RNA polymerase moves along the DNA template, it synthesizes mRNA in the 5' to 3' direction.
- Termination: Transcription continues until RNA polymerase encounters a termination signal in the DNA sequence. At this point, RNA polymerase and the newly synthesized mRNA molecule are released from the DNA template.
- Processing: The initial mRNA transcript, called pre-mRNA, undergoes processing before it can be used by the cell. This includes capping, where a modified guanine nucleotide is added to the 5' end, and polyadenylation, where a string of adenine nucleotides (poly-A tail) is added to the 3' end. Additionally, introns (non-coding regions) are removed from the pre-mRNA through a process called splicing, leaving only the protein-coding exons intact.
- Export: Once processing is complete, the mature mRNA molecule is transported out of the nucleus and into the cytoplasm, where it can be translated into protein by ribosomes.
This process of transcription allows the genetic information encoded in DNA to be transcribed into a complementary mRNA molecule, which serves as a template for protein synthesis. The regulation of transcription, including the activation or repression of specific genes, plays a crucial role in controlling gene expression and determining cellular function and identity.
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