Problem 162 - Objective Biology for NEET

Question

Assertion: \(\mathrm{Ca}^{2+}\) ion plays important role in muscle contraction Reason: Calcium ion binds to subunit of troponin on actin filament and removes the masking of active sites for myosin

Step-by-Step Solution

Answer

Yes, the assertion is correct, and the reasoning provided is an accurate description of how \(\mathrm{Ca}^{2+}\) ions play an integral role in muscle contraction by binding to troponin and uncovering the active sites on actin for myosin binding, which leads to muscle contraction.

Step 1: Interpret the Assertion

Consider the statement: '\(\mathrm{Ca}^{2+}\) ion plays a vital role in muscle contraction'. This statement asserts that calcium ions are fundamental to the process of muscle contraction.

Step 2: Interpret the Reason

Consider the reason: 'Calcium ion binds to the subunit of troponin on actin filament and removes the masking of active sites for myosin'. Essentially, this statement is describing the role of calcium in the molecular mechanism of muscle contraction. In the presence of calcium ions, they bind to the troponin complex on actin filaments, leading to a conformational change that results in the exposure of the active sites on actin for myosin binding. These interactions enable the sliding filament mechanism, leading to muscle contraction.

Step 3: Confirm the Assertion with the Reason

With the information given in the reason, it can be confirmed that the assertion is correct. The \(\mathrm{Ca}^{2+}\) ions play a major role in muscle contractions by facilitating the interaction between actin and myosin.

Key Concepts

Calcium Ions

Calcium ions (\( \mathrm{Ca}^{2+} \)) are crucial players in muscle contraction. They function as a signal that triggers various cellular processes, including the contraction of muscles. Here's how it works:- When a muscle receives a signal to contract, calcium ions are released from the sarcoplasmic reticulum into the cytosol of the muscle cell.- The increase in calcium ion concentration allows these ions to interact with various proteins within the muscle cell, initiating the contraction process.In essence, without calcium ions, the events leading to muscle contraction would not occur. They serve as the on-off switch that decides when muscles should contract and relax.

Troponin

Troponin is a complex of three proteins located on the thin actin filaments of muscle tissue. It plays a central role in regulating muscle contraction. - Troponin has binding sites where calcium ions attach. This interaction is essential because it causes a structural change in the troponin complex. - This structural shift moves tropomyosin away from the myosin-binding sites on the actin filament, allowing for muscle contraction to proceed. Thus, troponin acts as a mediator in the contraction process, responding to the presence of calcium ions and facilitating the interaction between actin and myosin.

Actin Filament

Actin filaments are one of the primary components of muscle fibers. They are part of the thin filaments that work alongside myosin to induce muscle contraction. - Actin itself is a globular protein that forms a double helix structure, creating the foundation of the thin filament. - The actin filaments have binding sites that, when exposed, allow myosin heads to attach and perform the contraction. The role of actin filaments is essential; they are the "tracks" along which myosin heads walk, driving the muscle contraction cycle. Their interaction with myosin is tightly controlled by troponin and tropomyosin.

Myosin Binding

Myosin binding is an intricate process that is vital for muscle contraction. The binding of myosin to actin is a key step in the contraction cycle. - In a relaxed muscle, myosin binding sites on actin are blocked by tropomyosin. - When calcium ions bind to troponin, it causes tropomyosin to shift, uncovering these sites. - Myosin heads, powered by ATP, then bind to the exposed actin sites and pull the thin filaments, resulting in muscle contraction. This cycle of binding, pulling, and releasing is what generates the force used in muscle movement and is a fundamental component of muscle contraction.

Sliding Filament Theory

The Sliding Filament Theory explains how muscles contract to produce movement. It describes the interaction between actin and myosin filaments within muscle cells. - According to this theory, contraction occurs when the myosin heads form cross-bridges with actin filaments. - Once the binding occurs, the myosin heads pivot, pulling the actin filaments toward the center of the sarcomere - the functional unit of a muscle. - This sliding of actin over myosin shortens the muscle fiber, leading to contraction. This theory provides an elegant explanation of the mechanical processes involved in muscle contraction, showing how the precise arrangement and movement of actin and myosin lead to the generation of force and movement.