05 proteins %26 cell structure


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05 proteins %26 cell structure

  1. 3. Neuronal structures and structural proteins Transmission Electron Microscopy Shows the different organelles in the cytosol
  2. 4. Golgi complex Is responsible for most posttranslational modification
  3. 5. <ul><li>Neurons are different from most other types of cells because they possess long processes: </li></ul><ul><li>What structures determine the characteristics of neuronal cytoskeleton? </li></ul>
  4. 6. Structural protein of the neuron <ul><li>Microtubules </li></ul><ul><li>Neurofilaments </li></ul><ul><li>Microfilaments </li></ul>
  5. 7. Microtubules <ul><li>Form long scaffold of neural processes </li></ul><ul><li>25% of total protein in neurons </li></ul><ul><li>Largest diameter 25 nm </li></ul><ul><li>Cylinder of 13 protofilaments – polarized </li></ul><ul><li>Composed of alternating  and  Tubulin subunits </li></ul><ul><li>- six genes and 20+ isoforms </li></ul><ul><li>- grows in size catalyzed by GTPase </li></ul><ul><li>The polymer is stabilized by MAPs </li></ul>
  6. 8. Microtubules grow in a helical fashion. Their growth is stopped by “capping” their growing end with GDP-bound tubulin. In the absence of MAPs or other stabilizeing proteins they depolymerize, disrupting the structure of the corresponding process MAP2: dendrites MAP3 and tau prot: axons
  7. 9. Map-2 staining in dendrites not axons
  8. 10. Neurofilaments <ul><li>Most abundant fibrillar protein in axons </li></ul><ul><li>10nm in diameter </li></ul><ul><li>Most abundant in axons </li></ul><ul><li>Related to keratin </li></ul><ul><ul><li>Very stable </li></ul></ul><ul><ul><li>Neurofibrillary tangles </li></ul></ul>
  9. 12. Microfilaments <ul><li>3-5 nm in diameter </li></ul><ul><ul><li>thinnest of the three elements of cytoskeleton </li></ul></ul><ul><li>Made of polarized actin monomers </li></ul><ul><ul><li>highly conserved and abundant in living things </li></ul></ul><ul><li>Highly dynamic </li></ul><ul><ul><li>half exists as monomers </li></ul></ul><ul><li>Many actin binding proteins secure cytoskeleton to plasma membrane </li></ul>
  10. 13. <ul><li>Actin is organized in small polymers, and is localized at the periphery of neurons, where it is responsible for shaping processes like growth cones and dendritic spines. </li></ul><ul><li> -actin is most abundant in the skeletal muscle </li></ul><ul><li> - and  -actin are present in neurons </li></ul>
  11. 14. <ul><li>The dynamic state of microtubules and microfilament allow the mature neuron to withdraw or extend old process and form new ones </li></ul>Morphological plasticity
  12. 16. Microtubule Domains in the axon
  13. 17. Microtubules and actin filaments are the TRACK along which proteins and organelles are moved by molecular motors
  14. 18. Molecular Motors <ul><li>Actin motors = myosin </li></ul><ul><ul><li>in muscle – actomyosin </li></ul></ul><ul><ul><li>Axons have polarized microtubules, giving rise to orderly movements of proteins from or to the cell body </li></ul></ul><ul><ul><li>Dendrites have NO polarized microtubules, giving rise to a more “disordered” morphologica structure, where proteins and organelles can be moved in either direction within the same volume </li></ul></ul>
  15. 19. Axonal transport Fast transport is two ways: from the soma to the terminal and viceversa Slow transport is only from the soma to the terminal Fast transport: organelles and functional proteins Slow transport: structural proteins
  16. 20. Fast axonal transport 410mm/day
  17. 22. Tubulin Clathrin Neurofilament Actin Slow axonal transport = 0.2-2.5mm/day
  18. 23. Both techniques are used by neuroanatomists for understanding the connectivity of the brain: anterograde and retrograde dyes
  19. 24. Inside the muscle similar proteins organize muscle spindles where information is sent using an axon for conveying somatosensory information
  20. 25. Similar proteins permit to study synapses between sensory neurons in the dorsal horn (red) and motor neurons in the ventral horn (green) of the spinal cord
  21. 26. Central neurons have a different morphology from spinal cord neurons: Pyramidal cells of the hippocampus
  22. 27. Spines can be considered as specialized organelles for performing spatially localized dendritic (input) functions
  23. 28. Dendritic Spines
  24. 31. http://multimedia.mcb.harvard.edu/anim_innerlife_hi.html