BIO273 Biology: Modification of mRNA - Seneca Polytechnic PDF

BIO273 Biology Flow of Information: Modification of mRNA Modification of mRNA  Once mRNA has been transcribed it must be modified in Nucleus Not all the nucleotide sequence will be used Splicing  Removal of unwanted RNA nucleotide sequences  Introns (In between usable code) S...

BIO273 Biology Flow of Information: Modification of mRNA Modification of mRNA  Once mRNA has been transcribed it must be modified in Nucleus Not all the nucleotide sequence will be used Splicing  Removal of unwanted RNA nucleotide sequences  Introns (In between usable code) Sequences not translated into Protein  Exons (are Expressed) Sequences the contain the amino acid sequence in a Protein SCHOOL OF BIOLOGICAL SCIENCES 2 AND APPLIED CHEMISTRY Spliceosome  Large complex molecular machine which removes Introns Editor that cuts out irrelevant data Composed of snRNA (small nuclear RNA) & Proteins  Creates snRNPs (small nuclear RiboNucleo Proteins) Pronounced “snurps” snRNPs  Recognize Intron sequences  Removes them  Ligates Exons together SCHOOL OF BIOLOGICAL SCIENCES 3 AND APPLIED CHEMISTRY Alternative Splicing  Splice out different Exons to create new mRNA strand Different mRNA strands will make different Proteins  Allows for a single gene to code for multiple Proteins  Surprise from the Human Genome Project Humans only have 20 000 genes & Majority of human genes are alternatively spliced SCHOOL OF BIOLOGICAL SCIENCES 4 AND APPLIED CHEMISTRY Modification of mRNA G-Cap  dGTP is added onto the 5’ end of the mRNA Helps the mRNA bind to the Ribosome in the Cytoplasm Poly-A Tail  50 – 300 dATP added to the 3’ end of the mRNA Protects the mRNA from enzymatic digestion in the Cytoplasm SCHOOL OF BIOLOGICAL SCIENCES 5 AND APPLIED CHEMISTRY Mature mRNA  Mature mRNA with only Exons, a G-Cap & Poly-A tail  mRNA now leaves the Nucleus & enters the Cytoplasm UTR = Untranslated Region SCHOOL OF BIOLOGICAL SCIENCES 6 AND APPLIED CHEMISTRY Summary  mRNA must be modified prior to leaving the Nucleus  Intron sequences are Spliced out, leaving only Exon sequences  snRNPs cut out Introns & Ligate Exons  Alternative Splicing can vary the Exon sequences  G-Cap is added to 5’ mRNA for Ribosome binding  Poly-A tail is added to 3’ mRNA for protection  Mature mRNA leaves the Nucleus for the Cytoplasm SCHOOL OF BIOLOGICAL SCIENCES 7 AND APPLIED CHEMISTRY