Final answer:
The degradation of mRNA in eukaryotes is a stepwise process that begins with post-transcriptional modifications such as splicing, capping, and polyadenylation within the nucleus. These modifications enhance the stability and functionality of mRNA, and after the mRNA is transported to the cytoplasm, its stability is regulated until degradation occurs.
Step-by-step explanation:
Various Steps of mRNA Degradation in Eukaryotes
The degradation of mRNA is a critical aspect of gene expression regulation and involves several sequential steps. Once mRNA is synthesized, it undergoes various modifications before it can be translated into proteins. The key post-transcriptional modifications include splicing, capping, and polyadenylation. These modifications occur within the nucleus and are essential for the stability and functionality of the mRNA molecule. Pre-mRNAs are first coated with RNA-stabilizing proteins, which protect the mRNA from degradation. The 5' cap is added to the growing transcript to assist in the initiation of translation and protect the transcript from degradation. The poly-A tail, which is a string of adenine nucleotides, is added to the 3' end, further stabilizing the mRNA and signaling for export to the cytoplasm. In the nucleus, introns are also spliced out, and the remaining exons are joined to generate the mature mRNA.
After the mRNA reaches the cytoplasm, its stability and lifespan are controlled by various factors. The lifespan or "shelf-life" of an mRNA in the cytoplasm is a characteristic known as RNA stability. This stability can be influenced by microRNAs (miRNA), which typically decrease stability and promote RNA decay. Eventually, all mRNAs are degraded in the cytoplasm, completing the mRNA life cycle.