have a head domain which is where the motor activity is. The head domain binds ATP and uses it to walk along the actin filament.
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How do Domains on the C terminus of the myosin motor proteins differ?
depending on what the cargo is Myosin 1,2, and 5 bind to lipid membranes Myosin 2 – its cargo is itself Myosin 5 has a similar structure to the kinesin motor proteins - Length of the leg is different between myosin 2 and 5
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Mutattion is some myosisn can cause what?
Deafness or blindness
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Myosin 1 does what?
I binds membranes and is involved in endocytosis
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Myosin 2 does what?
forms dimers that associate to each other in a bidirectionally symmetrical configuration to give rise to a myosin fibres
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Myosin 5 does what?
dimerises but does not form filaments - but binds via adaptor molecules to vesicles (for organelle transport/positioning), microtubules (to direct cell polarity) and RNA (for cell differentiation)
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How are Myosin II filaments formed?
from bi-symmetrical bouquets of Myosin II dimers. Each dimer is tied together by a coiled-coil tail region
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How can coiled coil tail region be removed?
by Chymotrypsin cleavge but the heads remain together. Further protease digeston with Papain removes the remainder of the tail(S2 region)leaving monomeric S1 heads which have the motor activity & both essential & regulatory light chain binding sites
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How do myosin heads move forward?
head binds ATP & is released from actin->hydrolysis of ATP to ADP & Pi->myosin head rotates into 'cocked' state->myosin head binds actin filament->'powerstroke':release of P&elastic energy straightens myosin;moves actin fil left->ADP released->start
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How are muscle cells formed?
By the fusion of myblasts
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muscle cells contain what?
A number of myofibrils each of which consists of a regular repeating array of sarcomeres, the base unit of muscle action
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what do the different bands contain?
The dark band are composed of myosin II filaments and the light band of actin filaments. The darkest region is the region of overlap containing both myosin filaments and actin filaments
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what happens to the bands when muscle contracts?
light band disappears as the region of overlap between the myosin and actin filaments increases.
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How are the ends of actin filaments capped?
The plus ends of the actin filaments are capped by CapZ which allows them to be buried in the Z disk. The minus ends of the actin filaments are capped by tropomodulin.
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What is nebulin?
a large molecule that has repeated actin binding sites and is thought to determine the length of the actin filaments
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What is titin?
one of the biggest proteins in the human body and is an elastic molecule that prevents over-stretching of the sacromere. When you pull a muscle you rip the titin protein apart (ouch).
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How does myosin bind to actin?
action potential->opening of a voltage gated Ca++ channel which release a small burst of Ca++ into the cytosol->Ca++ binds to a channel in the SR which triggers massive and explosive release of Ca++ into the cytosol, increase in calcium conc->bind
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Elevated Ca++ concentration causes what?
conformational change in two accessory proteins, tropomyosin (TM) and the troponin (TN) complex
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Cytokinesis in non-muscle cells depends on what?
a contractile ring of actin and type II myosin.
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Describe how myosin bundle formation at the cleavage furrow and constriction of the actomyosin ring occurs?
. During mitosis Cyclin B / CDK1 phosphorylates myosin light chain (MLC) and this prevents Myosin II from functioning. When CDK1 is inactivated at anaphase dephosphorylation of MLC allows myosin light chain kinase (MLCK) to phosphorylate MLC at Ser19
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How can The step size of a myosin motor can be calculated?what does it allow us to look at?
by laser based optical tweezers-actin filament tethered to a couple of beads within an optical trap and myosin motor proteins are allowed to work on that actin filament. When they start moving on it, the optical trap moves away-speed&duty cycle
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My does myosin 5 have a longer neck region?
allows greater step than myosin ½ - important in myosin 5 involvement in organelle transport
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How does myosin 5 move?
by taking 72nm steps - this is almost exactly the distance between the successive helical turns on the actin filament so Myosin V walks down only one side of the actin filament.
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Other cards in this set
Card 2
Front
How do Domains on the C terminus of the myosin motor proteins differ?
Back
depending on what the cargo is Myosin 1,2, and 5 bind to lipid membranes Myosin 2 – its cargo is itself Myosin 5 has a similar structure to the kinesin motor proteins - Length of the leg is different between myosin 2 and 5
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