Cell Signals

• cell signaling


  communication between cells and their environments
• signal transduction


  conversation between signaling molecules
• what is endocrine signaling?


  long range, systemic signaling via hormones transported through bloodstream (animals) or sap (plants
• where are hormones made?


  endocrine cells
• what are examples of endocrine signaling?


  insulin, adrenaline, melatonin, estrogen, and testosterone
• what is paracrine signaling?


  signaling by proteins secreted into extracellular space
• where are the proteins produced for paracrine signaling?


  produced by ER and released from plasma membrane
• how are the proteins in paracrine signaling moved?

  diffusion
• what are examples of paracrine signaling?


  developing embryo, wound healing, and cancer
• what is autocrine signaling?


  type of paracrine signaling where a cell receives the signaling it makes (cell talks to itself)
• what is an example of autocrine signaling?


  cancer cells uses this to promote uncontrolled growth
• what is synaptic signaling?


  signaling from neurons to other cells
• how does synaptic signaling?

  electrical signaling (action potential) results in release of neurotransmitters stored in vesicles at the synapse
• what are examples of neurotransmitters?


  dopamine, glutamine, and GABA
• what is contact dependent (juxtacrine) signaling?


  direct, physical contact between cells
• what is a feature of contact dependent signaling?

  signal never leaves the signaling cell
• where can contact dependent signaling be found?


  the immune system and embryo development
• extracellular receptors


  for signals too big or hydrophilic to cross membrane, needs receptors on cell surface to transfer signal inside
• intracellular receptors


  for very small or hydrophobic signals that can cross membrane, bind to receptors inside cell or directly to enzymes
• how are signaling pathways used in different contexts?

  • different cells expressing different receptors
  • signal transduction being different within a cell
• what do response to cell signaling rely on?

  history and current state of the cell
• combination of signals dictate response, as cells are exposed to multiple signals at the same time which are integrated to cause different responses
• what is the difference between fast and slow response to signaling?

  depends on whether transcription and translation are needed for the response
• what are the 2 molecular switches of signaling pathways?

  • signaling by protein phosphorylation
  • signaling by GTP-binding proteins
• what is a feature of both molecular switches?

  both add a phosphate to a protein to activate it
• how does signaling by protein phosphorylation work?

  • phosphorylation usually activates an enzyme
  • protein kinases (enzymes) phosphorylate target proteins by transferring phosphate group from ATP to specific protein
• how does signaling by GTP-binding proteins work?

  • when bound to GTP, the enzyme is usually active
• when bound to GTP in GTP-binding proteins what does it do?

  turns ON
• when bound to GDP in GTP-binding proteins what does it do?

  turns OFF
• what is an example of intracellular receptor?


  steroid hormones
• how does steroid hormones work?

  • they can cross the plasma membrane and bind directly to receptors in cytoplasm
  • receptors relocate to the nucleus and act as transcription regulators
• what are the 3 classes of extracellular receptors?

  • Ion channel receptors
  • G protein-coupled receptors (GPCRs)
  • enzyme-coupled receptors
• where are ion channel coupled receptors primarily found?

  neurons
• how does ion channel coupled receptors work in neurons?

  convert chemical signal (signaling molecule) back into electrical signal (voltage)
• what is an example of ion channel coupled receptor?

  glutamate
• what is the most abundant neurotransmitter?

  glutamate
• what are the steps to GPCRs?

  1. signal molecules binds to a receptor protein, making it active
  2. the active receptor protein interacts with G-protein complex, which holds a GDP bound to the alpha subunit
  3. upon activation, the GDP is exchanged for GTP in the alpha subunit, which causes the alpha subunit to disassociate from the other complexes
• what does G-protein activation cause?

  enzyme activation (effective signal amplification)
• what is an example of G-protein activation causing enzyme activation?

  cyclin AMP (cAMP)
• what does caffeine do to cAMP?


  converts cAMP into AMP, which makes us jittery and alert