Transcription 3 Flashcards
What happens at the 3’ end of the mRNA?
Hundreds of residues of “A” are linked (poly-a tail).
What does the poly-a tail do?
appears to protect against nuclease action and helps the process of translation. Longer the poly-a tail, the longer a transcript tends to exist.
What does AAUAAA signify?
That a poly-a tail should be placed nearby in the mRNA
What does splicing do?
Removes internal sequences of RNA followed by joining of ends.
What are the removed internal sequences called?
Introns
What are the segments that make it into the final RNA called?
Exons
What sequences are common to all spliced RNA’s?
GU sequence at the 5’ end of the intron and an AG at the 3’ end of the intron. Also a third sequence, an A residue surrounded by pyrimidines
What is a lariat Structure?
It is a 5-2 bond that occurs after the residue of A attacks the phosphate of the phosphodiester bond at the 5’ end of the intron. Then attack by the 3’ end of the exon on the 3’ end of the intron joints the two exon ends and releases the intron as a lariat.
What does splicing provide?
Rapid evolution of proteins
Multiple forms of a protein based on a single gene sequence
RNA editing of eukaryotic mRNAS
Occurs when a base in mRNA is altered.
Example of RNA editing?
apoB100/apoB48 system in our bodies. An enzyme can recognize a CAA codon inside the mRNA and deaminate C to make it U. This in turn makes UAA, which is a stop codon and stops translation. Therefore mRNA can make two different proteins
What guides RNA editing?
Guide RNAs, which are partly complementary to an mRNAsequence. mispaired regions define where the modifications occur
tRNAs modification
3’ end where amino acid gets covalently attached and a cloverleaf-type structure in 2-dimensions. Three loops are part of the cloverleaf structure.
What are the loops of the cloverleaf structure in tRNA?
D-loop, an anticodon loop, and a pseudouridine loop
How does the 3’ end of tRNA usually end?
CCA
