Molecular biologyLesson 2 of 2 in the course Genes and Proteins

Eukaryotic Messenger and Structural RNA Processing

5 flashcards · 5 quiz questions · 5 match pairs · 5 fill-in sentences · English

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Summary

After transcription, a eukaryotic pre-mRNA is not yet ready to be translated. It must be protected, modified at its ends, and have its noncoding introns removed. These steps produce a mature mRNA that can leave the nucleus and be used by ribosomes.

Pre-mRNAs are coated with RNA-stabilizing proteins that help protect them from degradation while processing and export take place. Two important modifications are added to the ends of the transcript.

All flashcards

What is the 5′ cap, and what does it do?
It is a 7-methylguanosine attached to the 5′ end of pre-mRNA. It protects the RNA from degradation and is recognized by factors that help initiate translation.
What is the poly-A tail?
It is a stretch of about 200 adenine residues added to the 3′ end of a pre-mRNA by poly-A polymerase. It contributes to RNA protection and provides a binding site for a protein involved in export.
How do exons and introns differ?
Exons are retained in the mature mRNA after processing. Introns are intervening sequences removed from the pre-mRNA during splicing.
What is the role of a spliceosome?
A spliceosome is a complex of proteins and RNA molecules that recognizes intron-boundary signals, removes introns, and joins the remaining exons.
How does a mature tRNA connect an mRNA codon to an amino acid?
Its anticodon pairs with a complementary mRNA codon, while its amino acid-binding site carries the corresponding amino acid.

Quiz questions

  1. Which modification is attached to the 5′ end of a eukaryotic pre-mRNA?Answer: A 7-methylguanosine cap.
  2. What is one function of the poly-A tail on a eukaryotic pre-mRNA?Answer: It supports RNA stability and provides a protein-binding site involved in export.
  3. Which sequences are removed from a eukaryotic pre-mRNA during splicing?Answer: Introns.
  4. Why can an error that shifts the joined sequence by one nucleotide disrupt a protein?Answer: It can change the reading frame and alter the encoded amino acid sequence.
  5. In trypanosome mitochondrial RNA editing, how do guide RNAs help insert U residues?Answer: They pair with pre-mRNA, and their poly-U tails provide residues inserted where the guide RNA loops out.

Based on Biology 2e by Mary Ann Clark, Matthew Douglas, Jung Choi (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.

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