Gene expression

• The mechanism by which genetic information in a gene is expressed as a functional protein


  1. Transcription factors bind to promotor, enhancer or silencer regions of DNA

  2. Promotors are at the beginning of the gene, they're the binding site for RNA polymerase

  3. Activator proteins bind to enhancers

  4. Repressor proteins bind to silencers
• Transcription factors


  Regulatory proteins
• Controlling translation


  1. mRNA is broken down by nucleases

  2. Shorten poly A tail

  3. Remove 5' cap

  4. Degradation of mRNA by nuclease enzymes into RNA nucleotides
• Epigenesis


  Interaction between genes and their environment during development
• Epigenetics


  Study of changes in organisms caused by modification of gene expression, not genetic code changes
• Epigenetic tags


  Chemical markers that attach to DNA and influence transcription of genes
• Epigenetic tags


  • DNA methylation
  • Histone modification
• Genome


  All genetic info of an organism
• Transcriptome


  All RNA molecules transcribed at a specific time within a cell
• Proteome


  Complete set of proteins present in a cell at a given time
• Proteome


  • Larger than the genome due to alternative splicing of mRNA exons and protein modification
• Methylation of promotor regions and histones

  1. Methyl transferase attaches a methyl group

  2. Methyl groups attach to C in promotor regions, repressing promotor activity

  3. Tightly coiled histones reduce transcription
• Epigenetic tags remain through meiosis and mitosis, can be removed when producing gametes
• Factors affecting gene expression

  • Diet
  • Cigarettes smoke
  • Air pollution
  • Aging
• Air pollution


  Modifies DNA and histone methylation, leading to disease patterns and inflammation in the lungs and cardiovascular system
• Aging


  Changing methylation associated with developing cancer and neurological disorders
• Treatments


  Exercise and B vitamins
• Genomic imprinting


  Only one of the two inherited genes for a trait is expressed
• Genomic imprinting


  • Male lion + female tiger -> large male liger
  • Male tiger + female lion -> small male liger
• Monozygotic twins


  Shared placenta, genetically identical
• Dizygotic twins


  Separate placenta, genetically distinct
• Presence of biochemical molecules which a cell metabolizes

  Gene expression is impacted
• The lac operon


  1. Regulates the transcription of enzymes required for lactose metabolism

  2. Lactose is absent, repressor binds with the operator, RNA polymerase cannot bind to the promotor

  3. Lactose is present, lactose inhibits the repressor, RNA polymerase binds to the promoter, lactase is synthesized