• In Eukaryotes, mRNA transcript must be processed before can exit the nucleus and be used for translation → Pre-mRNA longer than post mRNA
  1. 5’ Cap: is added to the 5’ end of mRNA                                                                                                             
  • Guanine nucleotide with 2 additional phosphate groups (forms GTP)
  • Capping provides stability, protection from nucleases, and a point of attachment for small ribosomal subunit
  1. Poly-A-tail: attached to 3’ end of mRNA
  • Consists of many adenine nucleotides
  • Provides stability and controls movement of mRNA across the nuclear envelope
  • At 3’ end of the gene, there is a poly-A signal sequence at the last exon of the gene
    • It is transcribed into an RNA sequence that signals where the transcript is cleaved and the poly-A-tail is added
  1. RNA splicing: removes nucleotide segments from mRNA
  • mRNA (and DNA) contain two kinds of sequences                                                                       
    • Exons: express code for polypeptide
    • Introns: intervening sequences that are noncoding
      • Allow for exon shuffling/alternative splicing
    • Uses spliceosomes: a large RNA-protein complex made on snRNA and proteins (snRNPs) that catalyzes the removal of introns & join exons
  1. Alternative Splicing: Selective excision of introns and retention of exons → allows diff mRNAs to be generated from same RNA transcript → each code for diff protein product of diff size
  • So single gene can code for proteins that are specific to cell type & developmental stage
  • Often diff exon combinations code for diff subunits (4th) of same protein