Exam Question Help

[jme611]

I have a molecular exam I am struggling with an any help would be greatly appreciated.
Questions:
1. Some retrotransposons and retroviruses integrate preferentially into regions of the chromosome that are (a) packaged in euchromatin and (b) located outside the coding regions of genes that contain information for making a protein. Why might these mobile genetic elements have evolved this strategy?
2. Is this statement TRUE or FALSE? Explain.
“Since introns do not contain protein coding information, they do not have to be removed precisely (meaning, a nucleotide here and there should not matter) from the primary transcript during RNA splicing.”

For #2 I believe that it is true. As long as there is only a a nucleotide here and there that remains there should be no issues when it comes to making a protein. I am unsure though. Once again any help would be greatly appreciated. Thank you.

[luisillo]

The first is to avoid deleterious mutations which would make the cell to die. If the cell dies the integrated genome also disappears. By inserting in non-coding regions they avoid messing up with cell's processes, cells then will continue to grow and divide replicating the inserted sequence as if it was theirs as well as the their (the cell's) entire genome. In fact, many of the non-conding regions of the genome are actually retrotransposable elements that were inserted there somewhere in time.

AS for the second, the statement is wrong are you make it worst by trying to justify it. You have to remember that in translation aminoacids are placed acording to a code of three bases called codon. I'll explain how wrong is #2 statement with an example:

Let's say you have this primary RNA sequence:

5'-AUGUGGGUCCAUGCAAGACAUUCGAAGUUGA-3'

The bold sequence are exons and the normal are introns, so after splicing it would be:

5'-AUG UGG GUC AGA CAU UGU UGA-3' This sequence would be translated to:

Met-Trp-Val-Arg-His-Cys (the last is the stop codon so does not code for anything).

Considering this, if a single nucleotide is taken away from the exon or an intronic nucleotide remains in the exon, that loss or gain will affect the translation of all the remaining sequence. Let's see it with the example sequence we have:

5'-AUG UGG GUC CAG ACA UUG UUG A-3' --> The bold letter is the extra one

Met-Trp-Val-Gln-Thr-Leu-Leu

As you see all the aminoacids change after the insertion of only a nucleotide an now there's not even stop codon which makes the produced protein useless (it degrades).

Well, it was a bit long, but I hope It can be useful for your exam.

The best of luck

[jme611]

Thank you so very much. This has helped immensely and I totally understand the logic behind the answer. Thanks again!