Block 3: Muscular System - Lecture 3.3 Flashcards
What is Cross Bridge cycling?
linking of actin to its attachment point on myosin
What proteins are involved in cross bridge cycling?
actin (thin filament)
myosin (thick filament)
What muscle action does cross bridge enable?
contraction (shortening)
Where does cross bridge cycling take place?
Zone of Overlap
What must be exposed for a cross bridge to form?
myosin binding sites on actin
As the zone of overlap increases, what happens to force?
force increases
What causes tropomyosin to shift?
calcium binds to troponin, causing a conformation change in tropomyosin
What happens when tropomyosin shifts?
myosin binding sites are revealed to allow myosin heads to bind to actin to form a cross bridge
What is used by myosin for energy?
ATP on the ATP binding site of myosin
Once ATP binds to the myosin head, what happens to the myosin head?
ATP hydrolysis causing a the myosin head to become cocked
When the myosin head becomes cocked, what happens to the ATP?
ATP hydrolysis by the unbound myosin head to change ATP into ADP + Pi that remains bound to the cocked head
What are the four steps to cross bridge formation?
1) readying myosin head
2) binding myosin to actin
3) power stroke
4) detachment
What happens during the readying myosin head step of cross bridge formation?
ATP hydrolysis
What happens during the binding myosin to actin step of cross bridge formation?
myosin head binds to myosin binding site on actin to form the cross bridge
only occurs when calcium is present
What happens during the power stroke step of cross bridge formation?
myosin pulls thin filament towards midline
a. movement/power stroke caused by ADP + Pi
