Book : Molecular Biology
posted by
Posted by: CHELSEA
posted by
Writer CHELSEA

Chemistry of the Primary RNA Transcript Splicing Reaction and Alternative Splicing

image about


Splicing Step One

In the first step of primary RNA transcript splicing, the 2' –OH on the branch point A attacks the phosphoryl group of the G in the 5' splice site. This G is the boundary between the 5' end of the intron and the 3' end of the adjacent exon. The attack leads to the breaking of the phosphodiester bond between the 3' end of the exon and the 5' end of the intron and the formation of a new phosphodiester bond between the branch point A and the 5' end of the intron. As is illustrated in the figure above, the first splicing step breaks the primary transcript into two pieces. One piece contains the 5' end of an exon, with a new free 3' –OH. The other piece is a strange looking structure that resembles a lasso and as a result is called a lariat structure. The lariat contains the intron that is still connected to a second exon.

Splicing Step Two

In the second step of primary transcript splicing, the newly released 3' –OH of exon 1 attacks the phosphoryl group on the 5'-most nucleotide of exon 2. The resulting phosphodiester bond is the boundary between the intron and the second exon. The final products of the reaction are the two joined exons and the intron, which is still in the lariat structure.

Alternative Splicing


Alternative splicing is a way of introducing diversity to the gene products of transcription by creating multiple protein products from the same DNA sequence. Alternative splicing accomplishes this in two ways: 1) by splicing together exons from two different primary RNA transcripts in a process called trans- splicing; 2) by splicing out entire exons.



related articles

Prokaryotic DNA Transcription Elongation and Termination

Prokaryotic DNA Transc...

  • Basics
  • posted Date:2017 Sep, 16

ElongationThe elongation...

read more
Nucleotides and Nucleic Acids

Nucleotides and Nuclei...

  • Basics
  • posted Date:2017 Sep, 16

OverviewBoth DNA and RNA...

read more
Errors in DNA Replication

Errors in DNA Replicat...

  • Basics
  • posted Date:2017 Sep, 16

ErrorsThe low overall ra...

read more

Subscribe With Us For Daily Reading Lesson Materials