Question

ATP provides energy for muscle contraction by allowing for (a) An action potential formation in the muscle cell. (b) Cross-bridge detachment of myosin from actin. (c) Cross-bridge attachment of myosin to actin. (d) Release of \(\mathrm{Ca}^{2+}\) from sarcoplasmic reticulum.

Short answer

The correct answer is (b), ATP provides energy for muscle contraction by allowing for cross-bridge detachment of myosin from actin.

Step-by-step solution

Understand Muscle Contraction

Muscle contraction is a complex process that involves various proteins and compounds. Among them are actin and myosin, two proteins that interact to cause contraction, and \(\mathrm{Ca}^{2+}\) ions, which play a key role in triggering contraction.

Understand ATP's Role in Muscle Contraction

ATP, short for adenosine triphosphate, provides the energy for several processes within cells. In the context of muscle contraction, ATP has a specific job: it allows myosin to detach from actin after the power stroke, resetting the system for another contraction cycle. Without ATP, myosin would remain stuck to actin, preventing further contractions.

Match the Role of ATP to the Options

Given the choices in the exercise, we are looking for the one that describes the detachment of myosin from actin.

Key concepts

Muscle Contraction

Muscle contraction is a vital process for movement and involves an intricate series of steps. The journey begins when a signal from the nervous system reaches a muscle cell. This triggers the release of calcium ions (\( \mathrm{Ca}^{2+} \)) inside the cell, which plays a pivotal role in the contraction process. These calcium ions bind to specific proteins within the muscle fibers, allowing two main proteins—actin and myosin—to interact.
As a result, the muscle fibers slide past each other, shortening the muscle, and causing contraction. This sliding mechanism is what generates force and allows us to move. Every contraction and relaxation cycle is tightly regulated, ensuring smooth and coordinated muscle movements.

• Signal initiation by nervous system.
• Release of calcium ions.
• Interaction of actin and myosin.

Myosin-Actin Interaction

The interaction between myosin and actin is at the heart of muscle contraction. Myosin is a motor protein that, together with actin, forms a structure known as a cross-bridge. This interaction is powered by ATP, which is crucial for the cycling of myosin heads during contraction.
Initially, myosin heads bind to actin filaments to form a cross-bridge. ATP then binds to myosin, causing a change that allows myosin to detach from actin. After ATP is broken down into ADP and inorganic phosphate, the myosin head changes shape, pulling the actin filaments and causing a power stroke. The cycle then repeats, leading to continuous muscle fiber contraction and relaxation.
This ATP-fueled interaction ensures that muscle fibers can repeatedly contract and relax, making movement possible.

• Myosin forms cross-bridge with actin.
• ATP detaches myosin from actin.
• A power stroke is generated by myosin movement.

Role of Calcium in Muscle Contraction

Calcium ions (\( \mathrm{Ca}^{2+} \)) are fundamental in regulating muscle contraction. These ions are stored in the sarcoplasmic reticulum, a specialized structure within muscle cells. When a muscle cell receives a signal to contract, calcium ions are released into the cytoplasm.
Their primary role is to bind with troponin, a regulatory protein found on actin. This binding causes a conformational change, moving tropomyosin away from the binding sites on actin, allowing myosin heads to attach and initiate contraction. Without calcium, these binding sites remain blocked, making contraction impossible.

• Calcium ions are released from sarcoplasmic reticulum.
• Calcium binds to troponin, revealing actin sites.
• Facilitates interaction between actin and myosin.

Calcium is thus a crucial trigger for muscle contraction, ensuring that actin and myosin can interact effectively.