front 1 what does actin form | back 1 microfilaments |
front 2 where is actin most likely present | back 2 cortex, below the plasma membrane |
front 3 what are the plural forms of actin | back 3 lamellipodia and filopodia (F-actin) |
front 4 what is the monomer of actin | back 4 G-actin |
front 5 How does actin exibit polarity | back 5 has a minus and plus end - show speed of shrinkage or growth |
front 6 What is the function of nucleations | back 6 allows for growth |
front 7 What happens in the step of nucleation? | back 7 the lag state - 3 G-actins form a nucleus (trimer) Slow step forms the nucleus |
front 8 What happens in the elongation state? | back 8 the growth phase - actin filament - rapid growth once nucleus formed |
front 9 What happens in the steady state? | back 9 the equilibrium phase - subunits being added and subtracted at equal rates rate of association = rate of dissociation (Cc) |
front 10 What is the significance of the plus and minus end of actin? | back 10 (-) end has a higher critical concentration growth and shrinkage can occur on both ends |
front 11 What is treadmilling? | back 11 growth on one end, and shrinkage on the other = no change in length both ends are constantly dynamic |
front 12 How is the ATP cap formed? | back 12 when the rate of G-actin added is greater than the rate of ATP hydrolysis - means constant growth |
front 13 what form of ATP when added? | back 13 ATP added ADP removed |
front 14 What are the three toxins for actin | back 14 Latrunculin - depolymerizes Cytochalasin B - depolumerizes Phalloidin - stabilizes (unable to disassemble) |
front 15 What are the three toxins for microtubules | back 15 Taxol - stabilizes (unable to disassemble) Nocodazole - depolymerizes Colchicine - depolymerizes |
front 16 What are the 2 proteins that modify G-actin? | back 16 Thymosin- inhibit addition of G-actin to bind on plus end Profilin - favors addition of G-actin to bind to plus end |
front 17 What are the 2 examples of an actin nucleator? | back 17 Arp 2/3: (branched actin) caps the minus end so only growth occurs on the plus end Formin: (unbranched actin) see-saw back and forth - bound to plus end and adding G-proteins on the plus end |
front 18 What is the function of CapZ? | back 18 prevents growth and shrinkage on the plus end (cap) |
front 19 What is the function of the tropomodulin? | back 19 prevents growth and shrinkage on the minus end (cap) |
front 20 what is tropomodulin? | back 20 a type of capping protein |
front 21 Where can capping proteins be found? | back 21 skeletal muscle cells |
front 22 what is the significance of these actin filaments being capped? | back 22 this ensures only sliding is occurring between the different actin forms (no shrinking or growing) |
front 23 What is the function of cofilin? | back 23 an actin severing protein - forces filament to twist tightly until breaks - allows for broken actin to be recycled and added to the top as ATP |
front 24 What are the 2 actin bundling proteins? | back 24 fimbrin - shorter protein, holds actin closer together Alpha-actinin - longer protein, holds actin farther apart |
front 25 What type of bundling protein is used for a contractile bundle? | back 25 alpha - actinin (need more space to but motor protein between them) |
front 26 what type of bundling protein is used for a tight parallel bundle? | back 26 fimbrin (prevents myosin II from entering bundle) |
front 27 What is the motor protein for actin? | back 27 myosin |
front 28 What is the structure of the actin motor protein that creates the contractive properties? | back 28 skeletal muscle myosin II - 2 heavy chains and 4 light chains - in a coiled coil (alpha-helical domain) - flower like ends that join their stems creating a bare zone in the middle |
front 29 what is the function of active myosin? | back 29 motor fixed, filament is not 1. in rigor state (fixed) myosin head bound to actin filament 2. ATP molecule binds to myosin head (loses affinity to actin filament) 3. myosin head hydrolyzes ATP and in cocked position 4. myosin head loses inorganic phosphate and has high affinity to bind to actin filament 5. loses ADP and changes conformation - in straight position and slides the space to a G-actin) |
front 30 when is the myosin II muscle contraction active? | back 30 Ca2+ released |
front 31 What are the functions of the Z-discs? | back 31 there are 2 z-discs on both ends of a sarcomere. this creates the contractile unit of a skeletal muscle cell that shortens length by sliding |
front 32 What are the 2 proteins that regulate skeletal muscle contraction? | back 32 Tropomyosin - binds filament groove, covering the myosin binding site (no nerve signal bc in the way) Troponin - binds with Ca2+ and pulls tropomyosin out of myosin binding site so contraction can occur (nerve receives signal) |
front 33 What activates myosin II contraction? | back 33 phosphorylation of the light chains (starts in a folded inactive state, then gets phosphorylated and changes confirmation to form a baby filament) |
front 34 What does the barbed end and the pointed end mean in actin filament? | back 34 pointed end - plus side barbed end - minus side |
front 35 What end is the critical concentration point always higher? | back 35 minus end |
front 36 what does it mean if you have a ATP cap? | back 36 that actin is actively growing |
front 37 How does formin grab G-actins? | back 37 by working with profilin which is a protein that favors the addition of G-proteins on the plus end |
front 38 Where do we find branched actin? | back 38 in the cortex |
front 39 Where do we find unbranched actin? | back 39 in sweeping/ crawling - stress fibers, filopodia (finger-like projection on the surface of cells), and contractile ring |
front 40 what is the cortex | back 40 in side the cell near the membrane that helps the cell with structural support and shape |