Question

You have discovered a gene that is alternatively spliced to produce several forms of mRNA in various cell types, three of which are shown in the figure. The lines connecting the exons that are included in the mRNA indicate the splicing. You known that protein translation begins in exon 1. For all forms of the mRNA, the encoded protein sequence is the same in the regions of the mRNA that correspond to exons 1 and 10. Exons 2 and 3 are alternative exons used in different mRNA, as are exons 7 and 8. Which of the following statements about exons 2 and 3 is the most accurate?_____

(a) Exons 2 and 3 must have the same number of nucleotides
(b) Exons 2 and 3 must contain an integral number of codons
(c) Exons 2 and 3 must contain a number of nucleotides that when divided by 3, leaves the same remainder (that is, 0, 1, or 2).
(d) Exons 2 and 3 must have different number of nucleotides

Answer 1

Exons 2 and 3 in alternatively spliced mRNA must have a number of nucleotides that when divided by 3, leaves the same remainder to ensure the reading frame is maintained for correct protein translation.

Step-by-step explanation:

The student has asked about the properties of exons 2 and 3 in alternatively spliced mRNA and how they relate to protein translation starting from exon 1, with exons 1 and 10 being consistent across different mRNA forms. The most accurate statement about exons 2 and 3 is that they must contain a number of nucleotides that when divided by 3, leaves the same remainder. This ensures that the reading frame is preserved, and the splicing process can produce a functional protein. The necessity for exons 2 and 3 to have an integral number of codons or to have the same or different number of nucleotides is not specifically required as long as the reading frame is maintained. This is essential because errors in splicing that alter the reading frame can result in nonfunctional proteins, as the sequence of amino acids would be shifted.