Here's a breakdown of the processing steps that lead to mature mRNA:
1. Transcription: The DNA sequence of a gene is copied into a pre-mRNA molecule by an enzyme called RNA polymerase.
2. 5' capping: A modified guanine nucleotide (a "cap") is added to the 5' end of the pre-mRNA. This cap protects the mRNA from degradation and helps it bind to ribosomes for translation.
3. Splicing: Non-coding regions of the pre-mRNA, called introns, are removed. The remaining coding regions, called exons, are joined together to form a continuous sequence.
4. 3' polyadenylation: A tail of adenine nucleotides (a "poly-A tail") is added to the 3' end of the mRNA. This tail protects the mRNA from degradation and helps it exit the nucleus.
Only after these processing steps are completed does the mature mRNA molecule leave the nucleus and enter the cytoplasm, where it can be translated into protein.
Let me know if you'd like more details about any of these processing steps!
