Questions and Answers
What is the Sliding Filament Theory?
It is the process of muscle contraction involving the sliding of actin and myosin myofilaments past each other to shorten the length of each sarcomere.
What molecules are involved in the sliding filament theory of how a skeletal muscle contracts?
Myosin, Actin, Tropomyosin, Troponin, ATP, Calcium ions
What are the six steps of single cross bridge cycling?
- The influx of calcium, triggering the exposure of the binding sites on actin. 2. The binding of myosin to actin. 3. The power stroke of the cross bridge that causes the sliding of the thin filaments. 4. The binding of ATP to the cross bridge, which results in the cross bridge disconnecting from actin. 5. The hydrolysis of ATP, which leads to re-energizing and repositioning of the cross bridge. 6. The transport of calcium ions back to the Sarcoplasmic Reticulum.
An ___ brings about the release of calcium ions from the ______.
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Calcium ions flood into the cytosol & _____, causing a ________ of the troponin-tropomyosin complex. This conformation change ____ the binding sites on ___.
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The binding of myosin to actin brings about a _____ of the cross bridge, which results in the release of ___ & ___. At the same time, the cross bridge ___, pulling the ____ inward toward the . This movement is called the '.' The _____ has been transformed into the ____ of contraction.
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The release of the myosin cross bridge from actin triggers the ____ of the ATP molecule into ___ & ___.
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Calcium is _____ from the cytosol into the ____ by ____. As the calcium is removed, the troponin-tropomyosin complex again ____ the binding sites on ___.
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What are the three roles of ATP in the sliding filament theory?
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According to the sliding filament theory when a muscle contracts, what happens?
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Where is myosin found in skeletal muscle cells?
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What three protein molecules are thin filaments made of?
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What is the function of tropomyosin?
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What is the function of troponin?
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What causes the tropomyosin to cover back over actin binding sites?
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What causes the myosin binding sites on actin to be exposed?
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What are the two important binding sites found on cross bridges of myosin?
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Actin contains binding sites for?
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What is required to move calcium ions from cytosol back into the sarcoplasmic reticulum?
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Study Notes
Sliding Filament Theory
- Muscle contraction is primarily executed through the sliding of actin and myosin myofilaments past each other, shortening the sarcomere.
- Key molecules involved in the process include myosin, actin, tropomyosin, troponin, ATP, and calcium ions.
Single Cross Bridge Cycling Steps
- Calcium influx exposes binding sites on actin.
- Myosin binds to actin, initiating a power stroke that slides thin filaments.
- ATP binds to myosin, causing a disconnection from actin.
- ATP hydrolysis re-energizes and repositions the myosin cross bridge.
- Calcium is transported back to the sarcoplasmic reticulum, concluding the cycle.
Calcium Ion Dynamics
- An action potential triggers calcium ion release from the terminal cisternae of the sarcoplasmic reticulum.
- Calcium ions bind to troponin, altering the shape of the troponin-tropomyosin complex and exposing actin binding sites.
Power Stroke Mechanism
- Myosin undergoes a shape change during binding to actin, releasing ADP and inorganic phosphate.
- This shape change flexes the myosin cross bridge and pulls actin inward, termed the power stroke.
- Chemical energy from ATP is transformed into mechanical energy during contraction.
Myosin Cross Bridge and ATP
- Myosin releases from actin through hydrolysis of ATP into ADP and inorganic phosphate.
- The process of muscle contraction relies significantly on ATP for energizing cross bridges, facilitating disconnection from actin, and transporting calcium ions.
Protein Structures in Muscle Contraction
- Myosin is located in thick filaments; actin, tropomyosin, and troponin constitute the thin filaments.
- Tropomyosin prevents cross bridge binding by covering actin binding sites.
- Troponin functions to move tropomyosin aside, revealing the myosin binding sites.
Role of Calcium Ions
- Calcium ions released from the terminal cisternae bind to troponin to expose myosin binding sites on actin.
- The removal of calcium ions leads to tropomyosin covering the binding sites once again.
Importance of ATP
- ATP is essential for energizing the power stroke, disengaging myosin from actin, and powering calcium ion transport into the sarcoplasmic reticulum.
- Myosin binding sites on actin are crucial for contraction, and both ATP and actin have binding sites on myosin cross bridges.
Calcium Ion Transport
- Specialized ion pumps in the sarcoplasmic reticulum membrane are responsible for moving calcium ions from the cytosol back into the sarcoplasmic reticulum.
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Description
Explore the detailed mechanisms of muscle contraction through the sliding filament theory. This quiz covers key processes including single cross bridge cycling and calcium ion dynamics, critical for understanding muscle physiology. Test your knowledge on the role of actin, myosin, and ATP in muscle function.
