effect of chromatin structure on gene expression - DNA organized around histones into nucleosomes 

• DNA methylation - blocks accidental transcription of genes that are turned off
  • vertebrates have protein that binds to methylated base pairs, prevents transcription from starting
  • ensures that genes stay turned off when turned off
• coactivators add acetyl groups to amino acids in chromatin >> makes DNA accessible to transcription factors
• remove high order chromatin structure >> faster transcription

eukaryotic posttranscriptional control - uses regulatory proteins, small RNA 

• small RNAs - interacts directly w/ main gene transcripts to regulate gene expression
  • 21-28 nucleotides long
  • RNA interface - inhibition of genes by RNA
  • double-stranded RNA forms when 2 ends complementary to each other loop
  • dicer - enzyme that makes small RNAs
  • microRNAs (miRNA) - binds directly to mRNA, prevents translation
  • small interfering RNAs (siRNA) - degrades mRNA before they get translated
• epigenetic change - change in gene expression passed down in generations
  • not caused by changes in DNA sequence
  • due to changes in DNA packaging
• changing how strands twist >> changes which genes are more easily accessible for expression
• primary transcript - initial mRNA molecule copied by RNA polymerase
  • includes introns/exons
  • spliceosomes (made of snRNPs) cut out the introns
  • alternative splicing >> creates different proteins from same gene
• RNA editing - produces altered mRNA not coded for the genome, usually through deamination
• nuclear membrane makes sure that only completely processed transcripts reach the cytoplasm
• translation factors - controls how mRNA gets translated by ribosomes
  • translation repressor protein - binds to beginning of transcript >> mRNA can’t attach to ribosomes
• transcripts for regulatory proteins, growth factors less stable than other mRNA, more easily degraded by other enzymes