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Wize AP Biology Textbook > Transcription and Translation

RNA Maturation in Eukaryotes

Eukaryotic TranscriptionPrevious Section
Translation into ProteinsNext Section
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RNA Maturation in Eukaryotes

After transcription of eukaryotic pre-mRNA, three modifications occur before translation:
  • 5’ capping
  • Polyadenylation
  • Splicing

5’ capping

A modification to the 5’ end of the pre-mRNA, which consists of a methylated guanosine (7- methylguanosine). This cap allows for efficient translation and prolongs the stability of the mRNA.


Polyadenylation

A modification to the 3’ end of the pre-mRNA, which consists of several hundred “A” nucleotides to give a poly-A tail. Like the 5’ cap, the poly-A tail helps prevent RNA degradation and helps export pre-mRNA to cytoplasm.

Splicing

Eukaryotic genes contain introns and exons. The resulting mRNA is spliced to join together exons and remove introns. (Hint: think “exons are expressed; introns are in between.”)



Photo by CNX OpenStax / CC BY


Wize Concept
After these modifications, the pre-mRNA is now fully matured and can be called mRNA.

Splicing occurs in the nucleus and is conducted by proteins called spliceosomes. This has to be a very precise process since leaving nucleotides in can cause frameshift mutations that generate nonfunctional proteins.


Photo by OpenStax / CC BY
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Example: mRNA Transcription

Transcribe the following template strand of DNA. Identify where the cap and poly-A tail appear on the mRNA.

DNA:
3'- ATACCTCGACTAG-5'

The resulting mRNA would be:
5'-UAUGGAGCUGAUC- 3'

The cap would be linked to the 5' end of the sequence and the poly-A tail would added to the 3' end of the sequence.

Practice: Gene Splicing

The diagram represents regions around a gene encoding a mRNA. The translation initiation codon (AUG) is present in exon 1 of the mRNA. The stop codon (UGA) is present in exon 4.

What region of the primary transcript is removed from the mature mRNA?

Practice: Transcription In Eukaryotes


The diagram represents an mRNA with exons (shaded regions) and introns (white regions).

a) In order to create a protein with the regions I, II, IV, what splicing pattern is required?