5’ cap

Definition

The 5' cap is a modified guanine nucleotide added to the 5' end of eukaryotic mRNA shortly after transcription initiation. It plays critical roles in mRNA stability, nuclear export, and translation initiation.

5 Must Know Facts For Your Next Test

1. The 5' cap consists of a 7-methylguanosine molecule linked via a 5' to 5' triphosphate bridge.
2. Capping occurs co-transcriptionally, meaning it happens while the mRNA is still being synthesized by RNA polymerase II.
3. The 5' cap protects mRNA from degradation by exonucleases.
4. It is essential for efficient ribosome binding during translation initiation.
5. Involved in the regulation of nuclear export of mRNA to the cytoplasm.

Review Questions

• What are the primary functions of the 5' cap in mRNA processing?
• How does the addition of a 5' cap protect mRNA molecules?
• Why is the 5' cap important for translation initiation?

Related terms

Poly-A Tail: A stretch of adenine nucleotides added to the 3' end of eukaryotic mRNAs that aids in stability and export.

RNA Splicing: The process by which introns are removed from pre-mRNA and exons are joined together.

Exonuclease: An enzyme that degrades nucleic acids from their ends, either from the 3’ or the 5’ direction.