The cross-bridge cycle Flashcards
during contraction, thick filaments bind to thin filaments and pull them toward the M line. what is this movement called?
filament sliding
during filament sliding, it shortens the _________ and increases the _________.
sarcomere; amount of overlap within the sarcomere
during contraction, where does filament sliding occur?
in all sarcomeres within every myofibril in a muscle fiber
the process by which the cross-bridge pulls the thin filament
cross-bridge cycle
how does the cross-bridge cycle generally work?
individual cross-bridges bind to g-actin in the thin filament
- cross-bridge then applies force to thin filament
- drawing thin filament towards M line
How much does each cross-bridge pull the thin filament to the M line?
10nm
only some of the cross-bridges within the muscle fiber undergo cross-bridge cycles during contraction.
No, all cross-bridges undergo the cycle
cross-bridges go thru each cycle ___________ of other cross-bridges, so cycles are _______ ____________
independently; not synchronous
the cross-bridge is connected to the tail by a
flexible hinge region
What are the two positions the cross-bridge can shift into?
the cocked and uncocked position
Which angle is smaller? the cocked or uncocked position?
uncocked
movement to the cocked position is called
cocking
occurs when ATP binds to the ATPase site on the cross-bridge
-converts ATP to ADP and Pi
ATP hydrolysis
increases the affinity of myosin for actin
ATP hydrolysis
What causes cocking within the cross-bridge?
energy storage within the cross-bridge
ATP binding to the ATPase site does what to the affinity of myosin to actin?
decreases affinity
the cross-bridge cycle is dependent on ________ ________ and only occurs if the concentration of this in the sarcoplasm is high.
calcium ions
-the ATPase site is empty
- no stored energy in cross-bridge
- has high affinity for actin
- bound to thin filament
rigor
when does rigor end?
when ATP bind to the ATPase site
What does binding of ATP cause?
decreases affinity of cross-bridge for actin, causing the cb to unbind from thin filament
-ADP and Pi are now in the ATPase site
- energy is now stored in the cb
-cocking occurs
-affinity for actin increases
ATP hydrolysis
Pi is released from ATPase site causing
power stroke
-energy is released from the cb, moving it to the uncocked position
-movement to the uncocked position pulls thin filament towards M line
-only point in cycle where filament sliding occurs
power stroke
What is the last thing to be released from ATPase site?
ADP
What is the last thing to occur in the cb cycle?
cb is in rigor, and a new cycle begins
true or false. during muscle fiber contraction, the amount of overlap bw thick and thin filaments increases in each sarcomere.
true
thin filaments shorten during muscle fiber contraction (t or f? )
false
during muscle fiber contraction, a cb pulls a thin filament toward the Z disk (t or f? )
false
during muscle fib contraction, all cross-bridges go thru the cb cycle (t or f? )
true
the angle bw the cb and the tail is greater when the cb is in the cocked position (t or f? )
true
During rigor, the ATPase site is (bound or empty?)
empty
the affinity of myosin for actin decreases when
ATP binds to the cb
the cb moves to the cocked position when
ATP is hydrolyzed to ADP and Pi
the power stroke occurs when
Pi is released from the cb
energy becomes stored in the cb during
ATP hydrolysis
