Final answer:
An mRNA molecule can be shorter than its corresponding gene due to post-transcriptional modifications such as the removal of introns, the addition of non-encoding segments like the 5' cap and 3' poly-A tail, and alternative splicing which allows for various mRNA transcripts and protein products.
Step-by-step explanation:
Why Might an mRNA Molecule Be Shorter Than the Gene From Which It Is Derived?
One may observe that an mRNA molecule is shorter than the DNA gene from which it is derived because of post-transcriptional modifications such as splicing. During splicing, introns (non-coding regions) are removed from the pre-mRNA transcript, leaving only the exons that code for proteins. Not only does this process streamline the mRNA, but it also enables a single gene to produce multiple proteins through alternative splicing, where different combinations of exons are stitched together, thus generating different mRNA transcripts that lead to different proteins. Additionally, segments such as the 5' methylguanosine cap and 3' poly-A tail are added to the primary transcript for stability and export purposes, which are not part of the encoding DNA sequence.
Furthermore, other unique processes such as mRNA editing in the mitochondria involve guide RNAs that can add or remove nucleotide bases, creating further disparity in length between mRNA and DNA sequences. These post-transcriptional modifications are crucial for the accurate and efficient production of proteins and for the protection of mRNA molecules within the cell.