Diagram a eukaryotic gene containing three exons and two introns, the pre-mRNA and mature mRNA transcript of the gene, and a partial polypeptide that contains the following sequences and features. Carefully align the nucleic acids, and locate each sequence or feature on the appropriate molecule.

a. The AG and GU dinucleotides corresponding to intron-exon junctions
b. The +1 nucleotide
c. The 5' UTR and the 3' UTR
d. The start codon sequence
e. A stop codon sequence
f. A codon sequence for the amino acids Gly-His-Arg at the end of exon 1 and a codon sequence for the amino acids Leu-Trp-Ala at the beginning of exon 2

Question

Accepted Answer

Hi, everyone. Welcome back. Let's look at our next problem. In a eukaryotic gene, there are three axons and two introns. The lengths of the axons and enrons are as follows. Exxon 1, 150 base pairs. Exxon 2 75 base pairs, XON 3 100 base pairs, intron, 1 300 base pairs, intron 2, 200 base pairs. What is the percentage of the gene that is composed of exons choice? A 39.39%. B 45.25% C 20.35% or D 75.23%. So to calculate the percent of the gene that is composed of exons, so percent of gene that is Exxon, we will want to calculate total length of exxons divided by the total length of the gene. So first, let's add together the length of our three axons. So they're up here on our chart X on one Xon two X on three. So that would give us 150 plus plus 100 as those are the lengths of the three exxons. So that adds up to 325 as our total length of all of our exxons combined. And then we need to add up the total length of the gene. So we have 325 base pairs making up exxons. And to that, we need to add the length of the two enrons. So the two enrons are 302 100 base pairs, which is 500 total. So add 500 to the 325 base pairs of exxons and we'll have 825 base pairs as our total length of the whole gene. So the percent of our gene that is exxons will equal 325. Our total length of exxons divided by 825. Well, if you want to test, I'm really in a hurry, you could rule out for instance, choice D 75% right away because that just can't be right. But this is such a simple calculation. Although sometimes it's useful in multiple choice to evaluate answer choices that you can see are going to be way off. In this case, it's a simple division problem and doing something like that probably takes more time than doing the division. So we have our division here and we also need to express it in percent. I should have added that at the end of our equation. So we have our division total length of exxons divided by total length of gene. And we'll need to, of course multiply it by 100% after we do that division. So I will add in multiply it by 100%. And when I do that calculation, I get 39.39% which corresponds to choice A. So choice A is going to be my correct answer for the percentage of gene, the gene that is composed of exxons. See you in the next video.

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Key Concepts

Gene Structure

RNA Processing

Translation and Codons