Final answer:
In trypanosomes, RNA editing that adds uracil bases to the mRNA is mediated by guide RNAs (gRNAs), which serve as the catalysts for this process. Guide RNAs contain complementary sequences and uracil bases necessary for the insertion into pre-mRNA, correcting the reading frame to produce a functional protein.
Step-by-step explanation:
The enzyme involved in the RNA editing process, which catalyzes the addition of uracil (U) bases to the mRNA within the mitochondria of trypanosomes, is not a standard enzyme as seen in other cellular processes. Instead, guide RNAs (gRNAs) facilitate the editing. These gRNAs contain the necessary instructions for editing through complementary base-pairing sequences and provide the uracil bases needed for insertion into the pre-mRNA to correct the reading frame.
In contrast to standard RNA processing, where proteins and enzymes are the primary catalysts, RNA editing in trypanosomes is entirely mediated by RNA molecules, specifically the guide RNAs. This RNA-based editing could be an evolutionary remnant from prokaryotes, as mitochondria are believed to be descendants of ancient prokaryotic cells.
While eukaryotic pre-mRNAs undergo modifications that include 5' capping, 3' polyadenylation, and intron splicing, RNA editing in trypanosomes is a unique process where missing U nucleotides are added to pre-mRNAs post-transcriptionally to ensure the production of functional proteins. This is reflective of the unique nature of mitochondrial DNA in these protozoa.