Processing
In biochemistry, processing is both the post-transcriptional modification of eukaryotic RNA ( RNA processing for short ) and the post-translational modification of proteins ( protein processing for short ).
RNA processing
For more information, see the section Eukaryotic Pre-mRNA Processing in the article mRNA .
All modifications take place on the pre-mRNA , so that it can be exported from the cell nucleus as “mature mRNA” .
Various processes are summarized under RNA processing:
- Capping : attaching the 5 'cap structure . Shortly after the start of transcription , the 5'-end of the pre-mRNA being synthesized is converted into a structure called a “ cap ”, which protects the mRNA from digestion by 5'- exonucleases and phosphatases. Addition of a cap made of modified guanine .
- Splicing : splicing of the pre-mRNA into introns and exons . Non- coding introns are cut out.
- Polyadenylation : Attaching the poly (A) tail to the newly formed 3 'end of the pre-mRNA (up to 250 nucleotides long). This poly (A) tail facilitates the export of the mRNA into the cytoplasm and also protects the 3 'end from enzymatic degradation.
- RNA editing : changing one or more nucleobases . So z. B. by editing a new stop codon upstream of the old one, whereby the translation breaks off and u. U. a completely different protein is produced. Editing can vary from cell to cell.
Protein processing
Proteins can be processed by proteolysis , phosphorylation , glycosylation and many other reactions.