Nerve Muscle Synapse Lecture 7 Flashcards
What are the 6 key molecular participants in the sliding filament theory of muscle contraction?
- Myosin (thick filament)
- Actin (thin filament)
- Tropomyosin - regulatory protein that binds to actin
- Troponin - binds actin and tropomyosin - site of calcium binding
- ATP
- Ca2+ - released from sarcoplasmic reticulum
Which protein is a regulatory protein that binds to actin
Tropomyosin - regulatory protein that binds to actin
Which protein binds actin and tropomyosin and is the site of calcium binding
Troponin
Myosin has two binding sites: one that binds to ____ and the other that binds to _____
Myosin has two binding sites: one that binds to ATP and the other that binds to actin
How does myosin move from low energy state to the high energy state?
By hydrolyzing a molecule of ATP
In an unstimulated muscle. the position of the ______ covers the binding sites on the actin subunits preventing the myosin cross-bridges from forming
In an unstimulated muscle. the position of the tropomyosin covers the binding sites on the actin subunits preventing the myosin cross-bridges from forming
_____ is a component of the thin filament that has a binding site for calcium
troponin
How does troponin facilitate the movement of tropomyosin allowing the actin molecule binding to be accessed by the myosin?
Ca2+ released from the terminal cisternae bind to troponin
Causes a conformation change in the tropomyosin-troponin complex “dragging” the tropomyosin off the binding site
What are the 6 steps of cross-bridge cycling (muscle contraction)?
- The influx of calcium triggering the exposure of binding sites on actin
- The binding of myosin to actin
- The “power stroke” of the cross-bridge that causes the sliding of the thin filaments
- the binding of ATP to the cross-bridge = cross-bridge disconnects from actin
- hydrolysis of ATP = reenergizes and repositions the myosin cross-bridge = allows another cycle
- the transport of calcium back into the sarcoplasmic reticulum
What happens PRIOR to cross-bridge cycling?
Muscle AP propagated through the T-tubule system, causing the release of calcium from the sarcoplasmic reticulum into the cytosol.
Coupling is through DHP and ryanodine receptor
Cross bridge cycling:
Calcium binds to _____ causing a change in the ________ complex = exposes myosin binding sites on actin
Cross bridge cycling:
Calcium binds to troponin causing a change in the troponin-tropomyosin complex = exposes myosin binding sites on actin
The energy from the _____ of ATP puts the myosin head in its ______ state
The energy from the hydrolysis of ATP puts the myosin head in its High-energy state
The pivoting of the ______ causes the H-zone to shorten.
The pivoting of the myosin cross-bridge causes the H-zone to shorten.
What is important about when myosin binds to actin in terms of ATP?
Remember: when things bind there is a conformation change = actin binding to myosin = conformation change of myosin = ADP and Pi are booted off the myosin molecule
In cross-bridge cycling, the _____ energy of ATP is transformed into the _____ energy of contraction
In cross-bridge cycling, the chemical energy of ATP is transformed into the mechanical energy of contraction
What causes the disconnecting of Actin and myosin?
What are two examples when we don’t have enough ATP to allow the myosin to dissociate from the actin?
The binding of Actin on myosin = conformation change
- Muscle cramp = not enough ATP
- Rigor mortis = no ATP following death
The release of myosin cross-bridge from actin triggers:
Hydrolysis of ATP into ADP and Pi = myosin returns to high-energy conformation = binds to Actin
The powerstroke moves the _______ inward, shortening the ______
The powerstroke moves the thin filament inward, shortening the sarcomere
What are two situations of muscle contraction where ATP is required:
- Binding of ATP is essential for the release of myosin cross-bridge from actin
- the hydrolysis of ATP is essential for re-energizing and repositioning the Myosin molecule to begin another cross-bridge cycle (allowing myosin to bind to actin)
During contraction, all cross-bridges are neither ____ nor _____ at the same time
During contraction, all cross-bridges are neither bound nor disconnected at the same time
What are the two metabolic variations of muscle fibres?
White and Red
Differ in size and colouration
What causes the colour variation in the different types of muscle fibres?
Their different methods of synthesizing ATP
Which Muscle Fibre:
- Large diameter
- Reduced myoglobin
- surrounded by few capillaries (low amounts of O2)
- relatively few mitochondria
- high glycogen content
White Muscle Fibres
White muscle fibres are used for _____ _____ activity
Short, intense
(powerlifting)
Which muscle fibre:
- smaller diameter
- Large quantity of myoglobin
- surrounded by many capillaries (high O2)
- Numerous mitochondria
- Low glycogen content
Red Muscle fibres
Red muscle fibres synthesize ATP ______ than white muscle fibres
Slower
What kind of activity are red muscle fibres more important for
Long lasting, continuous, light muscle contraction
How does white muscle fibre generate ATP
Glycolysis - anaerobic
How do Red muscle fibres generate ATP?
Oxidative phosphorylation and the Krebs Cycle (aerobic)
“fast twitch glycolytic fibres” refers to what
White muscle fibres
“Slow twitch oxidative fibres” refers to?
Red Muscle Fibres
