What chemical modification constitutes the 5' cap added to eukaryotic pre-mRNA?
Answer and explanation
Correct answer: B. 7-methylguanosine linked via a 5'-to-5' triphosphate bridge
The 5' cap is a 7-methylguanosine residue linked to the 5' terminal nucleoside via an unusual 5'-to-5' triphosphate linkage. It protects mRNA from exonucleases and facilitates ribosome binding. The poly-A tail is added at the 3' end.
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