The spliceosome removes introns from pre-mRNA. Which RNA component of the spliceosome catalyses the transesterification reactions during splicing?
- A snRNAs U2 and U6 (particularly U6), whose catalytic RNA structures carry out both transesterification steps of splicing ✓
- B snRNA U1, which base-pairs with the 5' splice site and catalyses the first transesterification attack
- C snRNA U2, which base-pairs with the branch point adenosine and positions the 2'-OH for nucleophilic attack
- D snRNA U4, which is the catalytic component held in reserve until U4/U6 unwinding activates the spliceosome
Correct answer: A. snRNAs U2 and U6 (particularly U6), whose catalytic RNA structures carry out both transesterification steps of splicing
Explanation
The spliceosome is a ribozyme — its catalytic activity resides in the RNA components, particularly snRNA U6 and the U2/U6 RNA base-paired network at the core of the active site. U6 contains the metal-binding catalytic triad (analogous to group II self-splicing introns, the evolutionary ancestor of snRNAs). U1 and U2 provide substrate recognition (5' splice site and branch point, respectively), positioning the substrate for the catalytic steps carried out by U6. U4 sequesters U6 in an inactive conformation and must dissociate for activation.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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