introns - intervening sequences found in eukaryotic DNA 

• noncoding DNA that doesn’t show up in mRNA or proteins
• exons - coding sequences

RNA splicing - cuts apart primary transcript to make final mRNA 

• occurs in nucleus, before mRNA goes into cytoplasm
• snRNPs - recognizes intron/exon junctions
• spliceosome - large complex of snRNPs
  • removes introns by twisting them in lariat shape
• exon-shuffling - theory that intron-exon arrangements represent shuffling of functional units over time

alternative splicing - splicing primary transcript into many mRNAs 

• includes different sets of exons
• experienced by 35-59% of human genes
• makes 120,000 different mRNAs possible in human cells
• proteomics - study of proteins

differences between prokaryotic/eukaryotic gene expression 

• eukaryotic genes have introns, prokaryotic genes don’t
• prokaryotic mRNA contain transcripts for many genes, eukaryotic mRNA only contain transcript for 1 gene
• prokaryotes can start translation before transcription is done (no nucleus)
• 5’ cap and 3’ poly-A tail added to genes by eukaryotes
• 5’ cap starts translation in eukaryotes, AUG codon starts translation in prokaryotes
• eukaryotes have larger ribosomes