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Microtubules - Coggle Diagram

- - - - the - end grows slowly, but it is usually capped
  - - - after the nucleus is formed, the monomers are continuously added on the nucleus for polymerization
        
        when polymerization, the graph changes from a lag to a steady state
        
        if a nuclei is present, polymerization will occur a lot faster
        
        the point where the polymer can start forming is called the critical concentration (Cc)
        
        past this point, the filament starts forming and the monomer mass remains constant
        
        if question mention monomers, it is talking about actin, if dimers, it is talking about tubulin
        
        the problem with the graph is how long nucleation takes to occur. If long, can see lag, but if short, there is no indicator for nucleation
      - this causes a slight lag period
    - - gives the microtubule property of dynamic instability
        
        this is good to allow for transport to different areas of the cell
        
        dynamic stability dependent on the the GTP-beta tubulin cap promoting adhesion
        
        the beta subunits must be in GTP form for assembly for good adhesion
        
        hydrolysis happens at same time as assembly, but when it catches up, causes cohesion loosens, the ends fray and cause depolymerization
  - - - depolymerizes the microtubule
        
        useful to observe what happens when microtubule is not active
    - - stabilizes the microtubule
        
        useful to see what happens when microtubules that need to depolymerize don't depolymerize (i.e. mitosis)
  - - - regulated through phosphorylation which promotes disassembly
        
        they prevent disassembly even when below the Cc
    - - packing strength affects strength and transport ability of the microtubule
      - tau
        
        short projection domain
      - MAP2
        
        long projection domain
    - - EB1
        
        binding on + end increases stability but but also have other functions like transport
  - - - XMAP215
        
        they have TOG domains that bind to + ends slowing hydrolysis, allowing for better adhesion
      - CLASP
    - - Kinesin-13
        
        uses ATP hydrolysis to rip off the protein dimers
      - Stathmin
        
        binds to the tubulin dimers on the + end, promoting GTP hydrolysis and decreasing protofilament interactions
        
        works opposite to CLASP and XMAP215
- - - - together the dimer is about 110 kDa and about 8 nm in length
      - the dimers alternating between alpha and beta forms the protofilament
        
        it has polarity (different on each side) such that there is alpha on one side and beta on other
        
        13 protofilaments then come together that form the tubulin which is a hollow tube
        
        they are 25 nm and can be up to 100 micrometers long
        
        tubulin has polarity such that the alpha is - end and beta is the + end
      - dimer properties
        
        very stable
        
        can only be separated through proteasomes
        
        alpha can permanently bind to GTP (only)
        
        beta can hydrolyze GTP to GDP so it can bind to both
  - - - usually 13 protofilaments
      - found in cytoplasm
    - - 23 microfilaments
        
        adds 10 from singlet
      - found in cilia/flagella
        
        forms an axonemal microtubule
    - - 33 microfilaments
        
        adds 10 from doublet
      - found in basal bodies and centrioles
    - - microtubules are made in the microtubule organization center and allows for polymerization
        
        the main MTOC is the centrosome, but other MTOC are present such as poles during mitosis
        
        the centrosome has 2 centrioles perpendicular (plants don't have centrioles but have other MTOC)
        
        the polymerization of the singlet microtubules is caused by proteins in the pericentriolar matrix and not the centrioles (gamma tubulin and augmin)
        
        gamma tubulin ring complex
        
        found in the MTOC and acts as a nucleating site for microtubules
        
        1 more item...
        
        1 centriole is formed by a ring of 9 triplet microtubules and is surrounded by the pericentriolar matrix
        
        in mitosis, the mother and daughter centrioles are different for unknown reasons
      - as microtubules are assembled, they go to the + end and - end is in the MTOC
        
        exception: dendrite microtubules can go in opposite direction
      - microtubules can also be released (still follows same direction of + to -)