Final answer:
The 5' end of pre-mRNA is capped with a 7-methylguanosine cap to protect it from degradation and assist in initiating translation.
Step-by-step explanation:
In eukaryotic cells, the 5' end of pre-mRNA is capped as soon as it emerges from polymerase. During transcription, a special nucleotide known as 7-methylguanosine is added to the 5' end through a 5'-to-5' triphosphate linkage. This cap, also referred to as the 5' cap, serves critical functions including protection of the mRNA from degradation and recognition by protein synthesis factors to initiate translation by ribosomes.
This cap acts as a protective structure, preventing degradation of the mRNA and helping initiate translation by ribosomes. Factors involved in protein synthesis recognize the cap and facilitate the start of translation.