RNA Processing and Post-Transcriptional Control
From Pre-mRNA to Functional RNA
Processing Steps
Eukaryotic pre-mRNA undergoes 5' capping, splicing, and 3' polyadenylation before export from the nucleus. These modifications protect the transcript, aid translation initiation, and help define RNA identity.
Alternative Splicing
Alternative splicing allows one gene to produce multiple protein isoforms by selecting different combinations of exons.
RNA Fate Control
After processing, RNAs can be stored, transported to specific cellular regions, translated with different efficiencies, or degraded. miRNAs and RNA-binding proteins are major regulators of mRNA stability and translational output.
Common RNA Modifications and Roles
| Modification | Function |
|---|---|
| 5' cap | Protects RNA and aids ribosome recruitment |
| Poly(A) tail | Improves stability and translation |
| Splicing | Removes introns |
| Editing | Can alter codons or RNA behavior |
What does alternative splicing accomplish?
Alternative splicing expands protein diversity without increasing gene number.
Correct answer: Creates multiple RNA or protein isoforms from one gene
Why is the 5' cap important for translation?
The cap is recognized by initiation factors and stabilizes the transcript.
Correct answer: It helps recruit the translation machinery and protects the RNA from degradation.
Eukaryotic mRNA Processing
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1
Step 1: The nascent transcript receives a 5' cap.
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2
Step 2: Spliceosomes remove introns and ligate exons.
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3
Step 3: The 3' end is cleaved and polyadenylated.
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4
Step 4: Quality control checks the mRNA.
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5
Step 5: Mature mRNA is exported and translated or stored.
Which molecule commonly represses translation by base pairing with target mRNAs?
miRNAs usually form regulatory complexes that reduce translation or promote mRNA decay.
Correct answer: miRNA
How can RNA localization affect protein function?
Spatial control of translation supports polarity, development, and rapid local responses.
Correct answer: It ensures proteins are synthesized near the place where they are needed in the cell.