Upload
esther-lloyd
View
217
Download
2
Tags:
Embed Size (px)
Citation preview
RNA Processing
By: Kelvin Liu, Jeff Wu, Alex Eishingdrelo
Purpose
The purpose of RNA processing is to prepare RNA for translation
Background
mRNAs have three main parts:- 5’ untranslated region- Exons (coding sequence)- 3’ untranslated region
Prokaryotes
Does not occur in prokaryotic cells because they do not have a nuclei
Protein synthesis goes happens before transcription is even complete, no processing necessary!
Eukaryotes
Steps in Process- Addition of 7-methyl guanosine
cap at the 5’ end- Addition of a poly-A tail at the 3’
end- Removal of introns (RNA
splicing)
- Transport to the cytoplasm
5’ Cap- The first step of RNA
processing- Occurs during transcription- A Guanine group is added to
the 5’ end of triphosphate (ATP) linkage
- This end is methylated to create 7-Methylguanosine Triphosphate using the enzyme Methyltransferase
- Its purpose is to protect the mRNA against degradation from nucleases and act as a point of attachment in rRNA
Poly-A Tail
- The second step of RNA processing- After transcription, the 3’ end of a mRNA
sequence is cleaved by Ribonuclease downstream from a specific AAUAAA site
- The enzyme poly-A polymerase adds a few hundred adenine nucleotides at the 3’ end- It’s purpose is to protect the mRNA sequence from enzymatic degradation and help the mRNA sequence move through the nuclear envelope
RNA Splicing
- A strand of DNA contains exons and introns– Exons are the coding sequences– Introns are noncoding sequences– Only the coding sequence is translated
- The introns are removed from the mRNA sequences by spliceosomes with subunits called small nuclear ribonucleoproteins, or snRNPs.
RNA Splicing Mechanism
• Splice donor (GU)– Start, 5’
• Splice acceptor (AG)– End, 3’
• Branch site (A)– Close to the
end
Alternative Splicing• Splicing allows the cutting and
pasting of different combinations of exons together
• Each exon can code for part of more than one protein
• Introns can sometimes change to exons and vice versa
Prokaryotic Regulation• Remember that prokaryotes do not
use RNA processing • They can regulate specific protein
production by synthesizing a strand of RNA with multiple coding regions for multiple proteins – Clustered genes called an operon
Relation to other processes
- The processing of adding the 5’ Cap, Poly-A Tail, and splicing of RNA occurs in the nucleus. After this process is complete, the RNA strand is ready for translation- RNA Processing is the step in between transcription and translation that allows protein synthesis to occur.
Sources
• http://www.csun.edu/~cmalone/pdf360/Ch13-2RNAprocess.pdf
• http://www.uky.edu/Classes/BCH/401/daanotes/lec10/daal10.html
• AP Biology Notes• Images: Google