2.6 -- Muscle Filaments Flashcards
(21 cards)
What are thick filaments made of? Which part is the long fibrous part and which is globular?
Myosin, with a globular “head” and a long fibrous “tail”
What is the “working” part of the myosin?
Cross-bridge head
Globular head has:
1). What binding site?
2). What binding site?
3). What on which it can pivot?
4). What activity?
1). Actin-binding site
2). ATP-binding site
3). Hinge on which it can pivot
4). ATPase activity
The globular head of myosin binds ATP and splits off its terminal what?
Phosphate
What activates the globular head, causing it to pivot?
ATP –> ADP + Pi, as its now energized
What are the three main protein groups of thin filaments? Which two are regulatory proteins?
Actin polymers
Regulatory Proteins: Tropomyosin and troponin complex
What is made of 300-400 G-blank subunits in double row and twisted to form helix backbone?
Actin polymers
What do the regulatory proteins do at rest in thin filaments?
Stop myosin and actin interacting
What protein blocks myosin binding sites on actin and which holds the protein in place?
Tropomyosin, held in place by troponin
Where does calcium come from in all skeletal muscle?
Sarcoplasmic reticulum
When a thin filament is activated by Ca2+ by being released into the cytosol, what does calcium bind to?
Troponin
Once calcium has binded to troponin, what happens to it?
Moves tropomyosin away from the myosin-binding site on actin, allowing myosin to bind to actin
In a contraction, hydrolysis of bound ATP does what to the head (cocking like a trigger)?
“Energizes”
The energized head can do what?
Bind actin
Release of Pi pulls the trigger, producing what, which pulls thin filament toward the center?
Powerstroke
Cross-bridge head cycling is what?
Asynchronous, Synchronous
Asynchronous
After the power stroke, ADP is released and a new what binds? This makes myosin do what, restarting the cycle? This causes what shortening and force production?
1). ATP
2). Actin
3). Sarcomere shortening and force production
While the myosin is then energized, the thin filament is blocked and must be activated to allow a contraction. What element is contraction dependent upon?
Calcium
In the relaxed state, what is blocked and what is ready?
Thin filament blocked and myosin head ready
In the relaxed state, is the myosin bound to actin?
It is weakly bound
In order for cross-bridge cycles to continue, what must be in the cytoplasm?
Calcium
