The nucleophile of the first step of spliceosome-mediated pre-mRNA splicing is t

Question

The nucleophile of the first step of spliceosome-mediated pre-mRNA splicing is the: A) 2 hydroxyl of the branch point adenosine. B) 3 hydroxyl of a free guanine nucleotide. C) 3 hydroxyl of the 5 splice site exon. D) 2 hydroxyl of the 3 splice site intron. The nucleophile of the first step of spliceosome-mediated pre-mRNA splicing is the: A) 2 hydroxyl of the branch point adenosine. B) 3 hydroxyl of a free guanine nucleotide. C) 3 hydroxyl of the 5 splice site exon. D) 2 hydroxyl of the 3 splice site intron.

Explanation / Answer

The correct answer is option (A).

2 hydroxyl of the branch point adenosine.

Splicing is a process where the introns are excised and the exons are spliced together to form a functionl mRNA. In thi step the 2'-OH group of a branch point within the intron performs a nucleophilic attack on the first nucleotide of the intron at the 5' splice site. This reaction exposes the 3' end of the 5' exon and a circular RNA known as the lariat.

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