rna modification

RNA modification

• aka post transcriptional modification

• occurs in nucleus

• three modifications -

  • adds G-cap and poly A tail can be at same time as transcription

  • splicing

addition of the G cap

• modified guanine nucleotide at 5’ end

functions -

• protection: helps protect from enzymes that digest in the 5’ end

  • enzymes breakdown foreign virus RNA/DNA but we don’t want it to chew our own

• export: proteins bind the the cap and help guide mature mRNA out of nucleus

• translation initiation: helps mature mRNA attach to ribosome since ribosome binds to the cap to bring the mRNA to ribosome

addition of poly A tail

• adenine

functions -

• protection: helps protect from enzymes that digest from the 3’ end

• export: helps mature mRNA exit the nucleus

• translation: helps ribosome recognize the mRNA

RNA splicing

• DNA sequence is interrupting protein

• removal of introns - non coding sequences that intervene and don’t provide info to make protein

• joining of exons - coding sequence with info to make protein

• gets out of nucleus through nuclear pores

matured mRNA = G cap, poly A tail, spliced

are there benefits to having introns in genes?

enable alternative splicing!!

• removes introns with one attached exon → two exons so two different ways

• one gene into multiple proteins

• different sequences = different functions

*all eukaryotic genes contain introns, but not all genes use alternative splicing since it might only require one specific function

*pre determined, genes don’t splice in the moment