1. pre-mRNA is further modified before exiting the nucleus. Describe how the end

Question

1. pre-mRNA is further modified before exiting the nucleus. Describe how the ends of the transcript are modified and why these modifications exist.

2. Pre-mRNA in Eukaryotes also undergoes rearrangements before exiting the nucleus. These rearrangements allow for greater diversity of proteins from a single gene. Describe the rearrangements and comment on the evolutionary significance of this mechanism.

3. In the above modification to mRNA, what gets removed and what gets kept in the final transcript?

4. What are the major RNA/protein components of translation?

5. How do tRNAs know which amino acid to bring to the growing polypeptide?

6. How are ribosomes targeted for the ER?

7. What kinds of proteins would be made this way?

Explanation / Answer

1. The DNA of eukaryotes is present in the nucleus and it contains “introns,” which protect the gene from damage. The “intron” is a part of genome, which does not code for proteins. During transcription, these introns also get transcribed, and the pre mRNA contains introns. These introns are cut to form the mature mRNA, and the “exons” are spliced together. If the introns are not cut, the mRNA may code for non-functional proteins.

Alternative splicing, i.e. removal of different portions of genes of introns (so, a gene is intron sometime, and exon sometime) help in the synthesis of various proteins from the same mRNA. Thus, RNA splicing does not always results in the removal of same introns.

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