AP BIOLOGY

Detailed explanation-1: -E1-4 refer to the exons and I1-3 refer to the introns in the pre-mRNA transcript. Where on a pre-mRNA transcript does a spliceosome bind? Pre-RNA editing occurs in the cytoplasm and utilizes a complex called the spliceosome as a complex of active enzymes.

Detailed explanation-2: -The spliceosome is built in distinct steps. First, the U1 snRNP binds the 5’ splice site and the U2 snRNP binds the branch site. A number of other snRNPs (U4, U6 and U5) bind the pre-mRNA transcript forming the mature spliceosome complex.

Detailed explanation-3: -Spliceosomes are huge, multimegadalton ribonucleoprotein (RNP) complexes found in eukaryotic nuclei. They assemble on RNA polymerase II transcripts from which they excise RNA sequences called introns and splice together the flanking sequences called exons.

Detailed explanation-4: -Components of the spliceosome recognize special sequences at the intron ends called splice sites. The 5′ splice site (at the 5′ end of the intron) is initially bound by the U1 small nuclear RNP (snRNP), and the 3′ splice site is bound by the protein U2 auxiliary factor (U2AF) (3, 4).

Detailed explanation-5: -Pre-mRNA splicing is connected to transcription in vivo The splicing reaction is catalyzed by the spliceosome, a large ribonucleoprotein (RNP) complex that forms from the ordered assembly of five small nuclear ribonucleoprotein (snRNP) particles onto each intron (1, 2)(Figure 1).