M6:S1 Cellular control

• Gene expression

  Genes are transcribed and translated into proteins, but it doesn't just happen willy-nilly
• Genes can be switched on or off

  Not all the genes in a cell are expressed, they are selectively switched on or off
• All the cells in an organism carry the same genes (DNA) but the structure and function of different cells varies
• Gene expression and protein synthesis can be controlled

  At the transcriptional, post-transcriptional and post-translational level
• Transcription factors

  Proteins that bind to DNA and switch genes on or off by increasing or decreasing the rate of transcription
• Activators

  Transcription factors that increase the rate of transcription
• Repressors

  Transcription factors that decrease the rate of transcription
• The shape of a transcription factor determines whether it can bind to DNA or not
• The amount of certain molecules in an environment or a cell can control the synthesis of some proteins by affecting transcription factor binding
• Operon

  A section of DNA that contains a cluster of structural genes, control elements and sometimes a regulatory gene
• Operon

  • The lac operon in E. coli
• Introns

  Sections of DNA in eukaryotic genes that don't code for amino acids
• Exons

  Sections of DNA in eukaryotic genes that do code for amino acids
• Splicing

  Introns are removed from primary mRNA strands and exons are joined, forming mature mRNA strands
• CAMP


  A secondary messenger that relays messages from control molecules like hormones to the inside of the cell
• CAMP activating protein kinase A (PKA)


  CAMP binds to PKA, causing a change in its 3D structure and releasing the active subunits
• Body plan


  The general structure of an organism, e.g. the arrangement of body parts in the Drosophila fruit fly
• Hox genes

  Genes that control the development of body plans
• Gene expression


  Genes are transcribed and translated into proteins, but it doesn't just happen willy-nilly
• Genes can be switched on or off


  Not all the genes in a cell are expressed, they are selectively switched on or off
• All the cells in an organism carry the same genes (DNA) but the structure and function of different cells varies
• Gene expression and protein synthesis can be controlled

  At the transcriptional, post-transcriptional and post-translational level
• Transcription factors


  Proteins that bind to DNA and switch genes on or off by increasing or decreasing the rate of transcription
• Transcription factors


  • Activators increase the rate of transcription, repressors decrease the rate of transcription
  • The shape of a transcription factor determines whether it can bind to DNA or not
• The amount of certain molecules in an environment or a cell can control the synthesis of some proteins by affecting transcription factor binding
• Operon


  A section of DNA that contains a cluster of structural genes that are transcribed together, as well as control elements and sometimes a regulatory gene
• The lac operon in E. coli


  • Contains three structural genes (lacZ, lacY and lacA) that produce proteins to help the bacteria digest lactose
  • The regulatory gene (lacI) produces the lac repressor, a transcription factor that binds to the operator site when there's no lactose present, blocking transcription
  • When lactose is present, it binds to the repressor, changing its shape so it can no longer bind to the operator, allowing transcription of the structural genes
• Introns


  Sections of DNA in eukaryotic genes that don't code for amino acids
• Exons


  Sections of DNA in eukaryotic genes that do code for amino acids
• Splicing


  Introns are removed from primary mRNA strands and exons are joined, forming mature mRNA strands
• CAMP


  A secondary messenger that relays messages from control molecules like hormones to the inside of the cell
• CAMP activating protein kinase A (PKA)


  CAMP binding causes a change in PKA's 3D structure, releasing the active subunits and activating the enzyme
• Hox genes control the development of body plans in animals, plants and fungi
• Hox genes


  • They have highly conserved homeobox sequences that code for a homeodomain, which binds to DNA and acts as a transcription factor to activate or repress developmental genes
• Apoptosis


  Enzymes break down cell components, the cell shrinks and fragments, and the fragments are engulfed and digested
• Apoptosis and mitosis


  They create and refine the body plan by removing unwanted structures and producing new cells
• Genes that regulate apoptosis and the cell cycle can respond to both internal and external stimuli
• Mutation


  Any change to the base nucleotide sequence of DNA
• Types of mutations


  • Substitution
  • Deletion
  • Insertion
• If a mutation occurs in a gene, the primary structure (amino acid chain) of the protein it codes for could be altered