post-transcriptional modification

• RNA splicing

  • the post transcriptional modification of MRNA which enables eukaryotes to produce more proteins than they have genes
  • more than one protein produced from one gene
• 1. gene is transcribed producing pre-MRNA
  2. all introns and some exons removed
  3. remaining genes joined back up by enzyme complexes(sliceosomes)- same exons can be joined in a variety of ways to produce several different verisions of MRNA
• splicing

  • polypeptides are made during protein synthesis
  • introns and exons can be found within genes
  • during transcription, both introns and exons are transcribed to produce Pre- mrna
  • before pre-mrna leaves nucleus splicing occurs
• splicing stages(post-transcription modifications)

  1. non coding introns removed
  2. coding exon sections joined together
  3. MRNA molecule only contains coding sequences of the genes
• alternative splicing

  • exons of genes can be spliced to produce different mature MRNA
  • single eukaryotic gene can code for more than one polypeptide chain