A gene has four exons of 150, 210, 180 and 240 nucleotides…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A gene has four exons of , , and nucleotides. Between them lie three introns of , and nucleotides. The gene is transcribed into a hnRNA, which is spliced, capped and tailed with adenylate residues. Ignore the cap.
- How long is the hnRNA?
- How long is the RNA after splicing?
- How long is the mature mRNA with its tail?
- What per cent of the hnRNA is removed as introns?
Need a reminder? The key ideaShow
The RNA polymerase reads the template strand from 3′ to 5′ and builds the RNA from 5′ to 3′, with U in the place of T. The RNA has the sequence of the coding strand. A hnRNA loses its introns by splicing, gets a cap at the 5′ end and gets a tail of 200 to 300 adenylate residues at the 3′ end.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Given. Exons: . Introns: . Tail: .
Plan. Add the parts and take away the introns.
Step 1. (a) Exons: . Introns: . hnRNA: nucleotides.
Step 2. (b) After splicing only the exons are left: nucleotides.
Step 3. (c) With the tail: nucleotides.
Step 4. (d) .
Answer: ; ; ; .
Check. The hnRNA is about five times as long as the mRNA, and about four fifths of it is thrown away.
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