Cell Physiology Part 7 Flashcards
(30 cards)
According to the sliding filament theory, what happens to the overlap between actin and myosin filaments during muscle contraction?
The overlap between actin and myosin filaments increases. The thin filaments (actin) slide past the thick filaments (myosin).
Does the length of the actin and myosin filaments change during muscle contraction according to the sliding filament theory?
No, the lengths of the individual actin and myosin filaments remain the same. Only the degree of their overlap changes.
What are the primary protein components of the thin filament?
Actin, tropomyosin, and troponin
What are the key parts of a myosin molecule that are involved in muscle contraction?
The myosin head (which binds to actin), the tail, and the hinge region.
What are the steps in the cross-bridge cycle?
1.Resting fiber, crossbridge is cocked,
not attached to actin
2.crossbridge attaches to actin when troponin- tropmyosin binds with calcium
3.power stroke causes crossbridge to tilt ,filaments slide
4.A new ATP binds with myosin head, allowing it to release from actin
ATP is hydrolyzed for the next cycle
In the first stage of the cross-bridge cycle ,what is the state of the myosin head and what is bound to it?
The myosin head is energized (cocked) and not attached to actin. ADP and inorganic phosphate (Pi) are bound to it
What triggers the myosin head to attach to actin in the second stage of the cross-bridge cycle?
The presence of calcium, which binds to troponin and causes a shift in tropomyosin, exposing the binding sites on actin.
What occurs during the power stroke (third stage) of the cross-bridge cycle, and what is released from the myosin head?
The myosin head pivots, pulling the actin filament towards the center of the sarcomere (sliding the filaments). ADP and Pi are released.
What causes the myosin head to detach from actin in the fourth stage of the cross-bridge cycle?
The binding of a new ATP molecule to the myosin head.
What happens to ATP after the myosin head detaches from actin, preparing for the next cycle?
ATP is hydrolyzed into ADP and inorganic phosphate (Pi), which re-energizes (cocks) the myosin head.
What is the role of calcium ions in the cross-bridge cycle?
Calcium ions bind to troponin, leading to the exposure of myosin-binding sites on actin, allowing cross-bridge formation.
What are the two key functions of ATP in the cross-bridge cycle?
1.Providing the energy for the myosin head to be cocked (via hydrolysis).
2. Causing the detachment of the myosin head from actin.
What is the crucial role of calcium ions in the cross-bridge cycle?
Calcium ions bind to troponin, causing a conformational change in the troponin-tropomyosin complex. This uncovers the myosin-binding sites on actin, allowing cross-bridge formation.
What are the two essential functions of ATP in the cross-bridge cycle?
. ATP hydrolysis provides the energy for the myosin head to be energized and cocked.
2. ATP binding to the myosin head causes the detachment of myosin from actin, allowing the cycle to repeat.
hat are the roles of troponin and tropomyosin in regulating muscle contraction, and how is calcium involved?
Tropomyosin blocks the myosin-binding sites on actin in a relaxed muscle. Troponin, when bound to calcium, undergoes a conformational change that moves tropomyosin away from these binding sites, allowing myosin to bind to actin and initiate contraction.
What is excitation-contraction coupling?
The sequence of events by which transmission of an action potential along the sarcolemma (muscle cell membrane) leads to the sliding of myofilaments and thus muscle contraction.
What is the role of the action potential in excitation-contraction coupling?
The action potential travels along the sarcolemma and down the T-tubules, triggering the release of calcium from the sarcoplasmic reticulum (SR).
What are dihydropyridine receptors (DHPRs) and where are they located? What is their role in excitation-contraction coupling in skeletal muscle?
DHPRs are voltage-sensitive receptors located in the T-tubule membrane. In skeletal muscle, they undergo a conformational change in response to the action potential, directly triggering the opening of ryanodine receptors (RyR) on the sarcoplasmic reticulum.
What are ryanodine receptors (RyR) and where are they located? What is their role in excitation-contraction coupling?
RyRs are calcium release channels located in the membrane of the sarcoplasmic reticulum (SR). When opened (mechanically linked to DHPRs in skeletal muscle), they allow a large influx of calcium ions into the sarcoplasm.
What is the sarcoplasmic reticulum (SR) and what is its primary role in muscle contraction and relaxation?
The SR is an elaborate smooth endoplasmic reticulum in muscle cells that stores and releases calcium ions. Its primary role is to regulate intracellular calcium concentration, which is essential for the initiation and termination of muscle contraction.
How is calcium removed from the sarcoplasm to allow for muscle relaxation?
Calcium is actively transported back into the sarcoplasmic reticulum by the SERCA pump (Sarco/endoplasmic reticulum Ca2+-ATPase). Calcium is also pumped out of the cell via the Na+/Ca2+ exchanger (NCX) and the plasma membrane Ca2+-ATPase (PMCA), although SERCA is the primary mechanism for relaxation.
What is the role of ATP in the context of the SERCA pump?
ATP provides the energy for the SERCA pump to actively transport calcium ions against their concentration gradient back into the sarcoplasmic reticulum. This is crucial for muscle relaxation.
What factors influence the performance of muscle contraction?
•Muscle Muscle tension & load
• Constant length & constant tension
Depends on: preload & afterload & contractility & summation
What is preload?
Preload is the force on the muscle prior to contraction.
> * It sets the initial length of the muscle before contraction
