Quiz 2 pt 1(ch 33) current topics of cell bio.txt

  1. actin subunit characteristics
    • 1. Assymetric
    • 2. Assemble in head-to-tail arrays
    • 3. Polar
  2. Association/Dissociation rates of actin
    Faster growth at POSITIVE (barbed) end, due to more ATP entering vs exiting
  3. Actin assembly steps
    • 1. Nucleation: assembly of trimer of monomers, due to amt of actin, Mg and ATP
    • 2. Elongation
    • 3. ATP Hydrolysis
  4. Nucleation of actin, how it forms?
    • Dissociation is MORE than association, but eventually association catches up
    • seed (nucleus) forms
  5. ATP Hydrolysis
    • Phosphates dissociate from ATP-actin
    • Irreversible step
    • common in cytoskeleton and mech. of movement
  6. Actin assembly on chart (conc of polymer vs time)
    • 1. Lag phase: nucleation at low conc. of polymer
    • 2. Net assembly: at increased conc of polymer
    • 3. No net assembly: turnover..conc remains constant over time
  7. Actin binding drugs and fxns
    • 1. Cytochalasin: binds monomers at BARBED end, to STOP polymerization
    • 2. Latrunculin: binds monomers to STOP polymerization (both result in disassembly due to INCREASE dis at pointed end)
    • 3. Phalloidin: BINDS and STABILIZES filaments, also used for staining actin due to ability to be labeled
  8. Monomer binding proteins
    • Regulate Assembly pool of actin (intracellular conc. of ATP-actin)
    • Cooperate w Capping proteins to regulate actin filaments
    • Profilins: ubiq, high affin for NTP free actin, NOT for ADP-actin
    • BINDS to formin and acidic membrane lipids
    • interacts with CAPPING proteins to maintain actin monomer pool
    • Thymosins: vert. specific, BIND ATP-actin, inhibit assembly & NTP exch
    • ADF/coffin: BIND ADP-actin and stabilize ADP filaments, inhibit NTP exchange, PROMOTE Severing and disassembly
  9. Formin
    • Unbranched filaments which assist in nucleation and elongation
    • Genes (3 in yeast, 15 in mammals) nucleate specific filaments
    • Act as TETHERS for assembly competent actin
  10. Arp2/3
    • BRANCHES filaments that bind to actin
    • with WASp/Scar nucleation promoting factor: bring together (nucleate) branched filaments in areas where filament networks are assembled
  11. Capping and severing proteins
  12. Stimulate assembly or disassembly
    • Gelsolins: Bind barbed (Pos) ends, Blocking association and disassociation along with…Fragmin & Severin
    • Severin and Gelosins: can also act to sever filaments w Ca and SIDE binding
    • Tropomodulin: Caps Pointed (neg) ends of stable filaments
    • can cause severing: exposing free ends for assem/disassembly
    • ADF/coffin: also binds to ADP filaments to promote severing
  13. Side binding proteins
    • Nebulin: in skeletal muscle
    • Tropomyosin: involved in myosin-actin integration, makes Contaction
    • Caldesmon: works w Tropo and Ca to regulate Contaction in smooth muscle
  14. Actin binding proteins
    • Crosslinking proteins: Have 2 actin binding domains
    • Bind membrane proteins
    • Fimbrin/plastin, B-shet domains
    • a-actinin, spectrin, dystrophin
    • ABP-12, Filamin/ABP(actin binding domain)
  15. VASP
    • protein aiding in self asociation of actin filaments
    • (WASp acts to help with actin filament branching)
  16. Mutations and physio effects
    • Some seen to be essential: Arp2/3, Profilin, coffin in yeast
    • Some knockouts cause minor effects: gelsolin, a-actinin, severin, dystrophin
  17. Cell motility rates
    through polymerization/depol
Card Set
Quiz 2 pt 1(ch 33) current topics of cell bio.txt