View source for 5' cap

Eukaryotic [[pre-mRNA|pre-mRNA]] goes through a process of modification before it is able to bind to the [[rRNA|ribosomal RNA]]. This modification also adds stability and plays an important role in the removal of [[Introns|introns]] in the [[Pre-mRNA|pre-mRNA]]. The process of cap addition takes place rapidly after [[Transcription|transcription]] is initiated, the addition of a<span style="font-size: 13.28px;">&nbsp;</span>[[Guanine|<span style="font-size: 13.28px;">guanine</span><span style="font-size: 13.28px;">&nbsp;</span>]]<span style="font-size: 13.28px;">base to the 5’ end of the [[mRNA|mRNA]], followed by the addition of [[Methyl_group|methyl groups]] (CH<sub>3</sub>) to the [[guanine|guanine]] and the bases of one or two bases at the 5’ end of the [[mRNA|mRNA]]. Unlike the rest of the bases in [[RNA|RNA]] the [[guanine base|guanine base]] constituting the 5’ cap is connected to the RNA by a 5’-5’ bond. The methyl groups are then added to position 7 on the [[guanine nucleotide|guanine nucleotide]]. Cap binding proteins then bind this structure allowing recognition by the ribosomal RNA. The rRNA will then move downstream until it reaches the [[start codon|start codon]], initiating translation. The addition of this cap is catalysed by the enzyme that associates with [[RNA polymerase II|RNA polymerase II]]. [[RNA polymerase I|RNA polymerase I]] and [[RNA_polymerase_III|III]] do not have this property and so RNAs modified by these enzymes don’t have the 5’ cap.</span> 

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