Molecular Biology Lecture #10

Front 1

What 3 major modifications does RNA undergo before being exported to the cytoplasm from the nucleus?

Back 1

Addition of a 5' guanosine capping nucleotide
RNA splicing
Cleavage at 3' end of mRNA and polyadenylation

Front 2

What is the point of the 5' cap?

Back 2

It is a substrate for multiple methylation reactions. Capping increases mRNA stability, participates in nuclear-cytoplasmic transport of mRNA's and is essential for initiation of translation

Front 3

How does mature RNA enter the cytoplasm?

Back 3

Through the nuclear pore

Front 4

What carries out RNA splicing?

Back 4

The spliceosome - contains both proteins and small RNA molecules (snRNA)

Front 5

What is the function of small RNA?

Back 5

They guide the activity of splicing proteins.
snRNP = snRNA + about 10 specific proteins. These are the functional units of the spliceosome

Front 6

How does RNA splicing through a lariat intermediate work?

Back 6

The 5' exon/intron junction is cleaved first releasing the 5' exon. The 5' end of the intron becomes linked to the invariant adenosine forming the lariate intermediate. The 5' exon then attacks the 3' splice site joinin ght e two exons and releasing the intron.

Front 7

What is the first step of the splicing reaction?

Back 7

The U1 snRNP identifies the 5' splice site and U2 binds the branch site.
snRNPs recognize the splice junctions.

Front 8

This catalyzes Lariat formation

Back 8

snRNA U6 - by binding to both U1 and U2

Front 9

What regulates this step?
How?

Back 9

U4
Inhibits U6 by preventing the latter from folding into its catalytically active structure.

Front 10

What is U5 required for?

Back 10

cleavage of the 3' intron-exon boundary.

Front 11

How does polyadenylation work?

Back 11

A specific sequence at the 3' end of the RNA (AAUAAA) is required for cleavage by a nuclear endonuclease. PolyApolymerase then synthesizes a poly A tail at the 3' end of the cleaved RNA. This stabilizes the mRNA.