Final answer:
Intron excision during RNA splicing involves the formation of a lariat structure, which is different from components of DNA replication such as replication forks, Okazaki fragments, and the helicase complex.
Step-by-step explanation:
Intron excision involves the formation of what structure? The correct answer is c) Lariat structure. During the process of splicing in eukaryotic cells, introns are removed from the pre-mRNA transcript to produce a continuous exon-only mRNA molecule. The splicing process involves the formation of a looped 'lariat' structure, which is created when the 5' end of the intron is attached to the branch point adenine within the intron. This lariat structure is subsequently excised and degraded, leaving a mature mRNA composed of exons ready for translation.
On the other hand, other terms mentioned such as a) Replication fork, b) Okazaki fragments, and d) Helicase complex are associated with DNA replication, not RNA splicing.