A protein-coding gene has 10 exons, 100 bp each, and 9 introns, 1,000 bp each What is the size of mature mRNA?
The correct answer and explanation is:
The size of the mature mRNA is 1,000 base pairs (bp).
Here is how to calculate this:
The gene has 10 exons, each 100 bp long. Exons are the sequences that remain in the mature mRNA after RNA processing. The total length of all exons combined is 10 × 100 bp = 1,000 bp.
The gene also has 9 introns, each 1,000 bp long. Introns are non-coding sequences that are removed from the pre-mRNA during RNA splicing, so they do not contribute to the length of the mature mRNA.
Mature mRNA is composed only of exons joined together after intron removal. Therefore, the size of the mature mRNA corresponds to the sum of the lengths of all exons.
In summary, the mature mRNA size is the total exon length, which equals 1,000 bp.
Explanation:
Genes in eukaryotes are typically composed of alternating exons and introns. During transcription, the entire gene, including exons and introns, is transcribed into a precursor messenger RNA (pre-mRNA). This pre-mRNA undergoes processing where introns are removed and exons are spliced together to form the mature mRNA. The mature mRNA contains only the exons and is ready for translation into a protein.
Since introns are removed and do not appear in mature mRNA, only the length of the exons is relevant for calculating mature mRNA size. In this problem, each exon is 100 bp long, and there are 10 exons, so the total length is 10 × 100 = 1,000 bp. The introns, being 1,000 bp each and 9 in number, are removed during processing, so their length does not affect mature mRNA size.
Therefore, the size of mature mRNA is 1,000 base pairs.