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Actin - Coggle Diagram

- - - - not much actin is available for polymerization
  - - - makes more actin available to polymerize by "activating" them
  - - - binds to + end
        
        binding to their respective end allows only the other end to polymerize
        
        if both sides are capped, the actin cannot grow or shrink as it is stabilized
    - - binds to - end
  - - - cytochalasin
        
        depol. actin filaments
      - phalloidin
        
        stabilize actin filaments
  - - - formin is regulated by Rho -GTP
        
        When Rho-GTP is in GTP form, it is the active form that activates formin
  - - - regulated by NPF (WASp/ WAVE)
        
        WASp
        
        activated by Cdc42
        
        for these to activate Arp2/3, they themselves need to be activated
        
        WAVE
        
        activated by Rac
      - to be activated, must be bound by WASp or WAVE
      - the branching is important for endocytosis and phagocytosis
        
        when branches are polymerized, they can pull the membrane inwards, form a vesicle and move it into the cell (endocytosis)
        
        a membrane can be pushed outwards in phagocytosis which pushes the membrane around the substance about to be engulfed
  - - - for this network to be held up, uses other proteins
        
        RBC
        
        ankrin anchors actin to the plasma membrane giving RBCs its shape
        
        muscles actin must be bound to the plasma membrane to work, so uses dystrophin
        
        no dystrophin means the muscle eventually dies
        
        microvilli uses ezrin to hold the PM in place and increase the surface area
- - - - actin is important for cell movement
  - - - globular protein with 4 domains
      - structure is non-sym due to the cleft
        
        give actin polarity
      - with polymerization of G-actin into F-actin, the cleft end (-) faces the opposite direction
        
        the + end polymerizes faster than the - end
  - - - filaments can then form on top with myosin acting as the nucleus
        
        similar to MT, without the nucleus, there is a lag phase, but when it forms, polymerization occurs faster
        
        the nucleus does not have to be actin monomers and many things can act as the nucleus
  - - - for polymerization to occur, actin must also be in ATP form
        
        ATP hydrolysis is not need for polymerization
        
        Cc for + end is 0.12 micromolar
        
        when the monomer concentration is between the two, the + end polymerizes while - depolymerizes
        
        creates treadmill effect that actin is moving from + to - end
        
        plus end is easier to pol., so lower number
        
        Cc for - end is 0.6 micromolar
- - - - heavy chain
        
        includes the head domain
      - light chain
        
        binds to the myosin's neck to regulated step size and step speed
    - - where the protein binds to actin and has ATPase activity
        
        ATPase activity is to move down actin
    - - myosin head domains are on the sides