Question

Explain how splicing occurs by labeling the 5’ss, the 3’ss the branch point and then tell me which snRNPs are used and where they play a part in the two transesterifications in splicing. You need to explain and show me the two transesterifications that happen in splicing.

Answer 1

RNA splicing is one of the forms of RNA processing, by which the the newly made RNA transcript is transformed into a mature messenger RNA.
During splicing, introns are removed and exons are joined together. splicing is carried out in a series of reactions which are catalyzed by the spliceosome, a complex of small nuclear ribonucleo proteins (snRNPs) for many eukaryotic introns.
A donor site, 5' end of the intron, a branch site, near the 3' end of the intron and an acceptor site, 3' end of the intron are required for splicing within introns.

The splice donor site includes an almost invariant sequence GU at the 5' end of the intron, within a larger, less highly conserved region. The splice acceptor site at the 3' end of the intron terminates the intron with an almost invariant AG sequence. Upstream (5'-ward) from the AG there is a region high in pyrimidines (C and U), or polypyrimidine tract. Further upstream from the polypyrimidine tract is the branchpoint, which includes an adenine nucleotide involved in lariat formation.
The consensus sequence for an intron is:
G-G-[cut]-G-U-R-A-G-U (donor site) ... intron sequence ... Y-U-R-A-C (branch sequence 20-50 nucleotides upstream of acceptor site) ... Y-rich-N-C-A-G-[cut]-G (acceptor site). the specific sequence of intronic splicing elements and the number of nucleotides between the branchpoint and the nearest 3’ acceptor site affect splice site selection. point mutations in the underlying DNA or errors during transcription can activate a cryptic splice site in part of the transcript that usually is not spliced.
a point mutation, which might otherwise affect only a single amino acid, can manifest as a deletion or truncation in the final protein.