Th1L06 Actin

Adjunto:

• Th1L06 Intermediate Filaments
• Th1L06 Microtubules

1. network of protein filaments that extend throughout the cell that determine:
   1. cell shape and polarity
   2. tissue structure
   3. adhesion
   4. cell movement
   5. intracellular movement (of vesicles and of chromosomes)
   6. essential to anchor cells to each other
   7. essential to anchor cells to anchor extracellular matrix at cell junctions

1. microfilament
2. composed of actin-binding proteins
   1. called F-actin
      1. filamentous actin or microfilament
      2. polymers of individual actin proteins called G-actin (globular actin)
3. polarised double helix
   1. 13 actin subunits for every complete turn
   2. 7nm diameter

1. (1) requires ATP to be bound to the actin monomer (G-actin)
   1. Not very stable over time
   2. ATP eventually hydrolyses to ADP and will depolarise and come off at the negative end
2. very dyanmic
3. monomers can be added and removed from both ends of the polymer
4. G-proteins add more rapidly to (+) end of the filament
   1. once incorporated, ATP is hydrolysed to ADP
5. G-protein is removed more rapidly from the (-) end of the filament

1. provide support
   1. Maintains the shape of cells
      1. erythrocytes
   2. absorption in the gut by forming an adhesion belt
      1. microvilli in gut
   3. detect vibration in the cochlea
      1. In sterocillia
         1. cells are depolarised or hyperpolarised by deflections caused by sound; actin filaments keep them rigid
   4. Cell migration
   5. modulate polymerisation dynamics and function
      1. e.g. myosin, capping proteins, severin, etc.
   6. required to hold synaptic vesicles close to the presynaptic membrane

1. e.g. migration of neutrophils (WBC) to sites of infection for phagocytosis
2. four events
   1. (1) cell pushes out protrusions at the front (leading edge) ○ actin filament polymerisation provides to force of membrane protrusion
   2. (2) ○ protrusions adhere to the surface on which the cell is moving through contact junctions; F-actin connects to the focal adhesions to provide a contractile force for the cell
   3. (3) the rest of the cell pulls against the anchorage points to drag itself forward
   4. (4) actin depolymerises at the rear
3. Lamellipodia

   Adjunto:

   • Th1L06 Lamellipodia (actin based movement)
   1. cytoskeletal protein actin projection on the leading edge of the cell
      1. extend and withdraw
      2. generated by rapid growth of actin filaments at the cell membrane
      3. the (+) end of actin filaments are oriented towards the periphery