Problem 6: Interpreting a pre-mRNA splicing diagram

[Anonymous]

Problem 6: Interpreting a pre-mRNA splicing diagram
The regions labeled A and C of the diagram are ___________________.


http://www.biology.arizona.edu/molecular_bio/problem_sets/mol_genetics_of_eukaryotes/graphics/q6.gif

A. introns
B. snRNPs
C. spliceosomes
D. exons
E. tRNAs




Spliceosomes

Splicing in the eukaryotic nucleus is catalyzed by spliceosomes, which are large RNA-protein complexes.
The RNA components of the spliceosome, known "snRNAs", participate directly in splicing reaction by interaction with intron consensus sequences and with each other.
There are six major types of snRNAs, which complex with proteins to forms snRNPs. As suggested by the diagram, the snRNPs assemble on the pre-mRNA to form the spliceosome.

http://www.biology.arizona.edu/molecular_bio/problem_sets/mol_genetics_of_eukaryotes/graphics/06t.gif


RNA splicing

RNA splicing occurs by a 2-step mechanism:
Step 1:
Cleavage of 5' exon-intron boundary and formation of intron-lariat; This is the first of two phosphodiester transfer reactions.

http://www.biology.arizona.edu/molecular_bio/problem_sets/mol_genetics_of_eukaryotes/graphics/06ta.gif


Step 2:
Joining of 5' and 3' exons together and release of the intron as lariat RNA, which is 2nd phosphodiester transfer reaction.

http://www.biology.arizona.edu/molecular_bio/problem_sets/mol_genetics_of_eukaryotes/graphics/06tb.gif


ans:
D. exons
The 5'- and 3'-exons are separtated by the intron. During the 2-step splicing reaction, the intron is removed and the exons are joined together.