Problem 166 - Objective Biology for NEET

Question

Assertion: Myosin is structural protein but also act as enzyme. Reason: Myosin is use to form myofibril and can hydrolyse ATP.

Step-by-Step Solution

Answer

The myosin protein, found in muscle fibers, not only helps in the formation of muscle structure but it also functions as an enzyme through its ability to break down ATP. Thus, affirming its dual role as a structural protein and an enzyme.

Step 1: Understanding Myosin

Myosin is an important protein found in muscle fibers, and plays critical roles in muscle contraction. This is the structural role it plays as a protein.

Step 2: Myosin and ATP

Not only is myosin a structural protein, it also possesses enzymatic properties, particularly as an ATPase. An ATPase is an enzyme that can break down ATP (adenosine triphosphate) into ADP (adenosine diphosphate). This process releases energy, which can be used for muscle contraction.

Step 3: The Duality of Myosin

Thus, myosin serves two roles: a structural one as a protein found in muscle fibers, and an enzymatic one as an ATPase, breaking down ATP for energy release. This understanding affirms the dual nature of myosin, which validates the assertion and the reason provided

Key Concepts

Structural Protein

Structural proteins are the building blocks of cells and tissues. They form the framework and architecture of muscles, giving them shape and support. Myosin is a prime example of a structural protein. It is located within muscle fibers and helps build the essential contractile units of a muscle called myofibrils.
Myofibrils are composed of repeating units called sarcomeres, which are the functional units responsible for muscle contraction. Structural proteins like myosin interact with other key proteins such as actin to form these repeating units.

• Myosin contributes to muscle integrity and resilience.
• It maintains the structural alignment necessary for muscle function.

By forming such a robust framework, myosin ensures that muscles retain their form and efficiently carry out their primary role of contraction.

ATPase

ATPases are enzymes that facilitate the breakdown of ATP (adenosine triphosphate), releasing energy needed for various biological processes, including muscle contraction. Myosin, beyond its role as a structural protein, acts as an ATPase.
This means myosin can catalyze the hydrolysis of ATP to ADP (adenosine diphosphate) and an inorganic phosphate group. This crucial reaction releases the chemical energy stored in the ATP molecule.

• ATP hydrolysis provides energy for myosin movement.
• Myosin's ATPase activity is essential for muscle contractions and other cellular motions.

By serving as an ATPase, myosin transfers the energy necessary for muscle fibers to shorten and generate force, which is vital for movement and overall function.

Muscle Contraction

Muscle contraction is a complex biochemical process that involves the shortening of muscle fibers to produce movement. Central to this process are myosin and actin, two proteins that work in tandem within the sarcomere, the fundamental unit of a muscle.
When a muscle is stimulated, myosin heads bind to actin filaments, forming cross-bridges. This initiates a series of events known as the sliding filament mechanism. Powered by the energy released from ATP hydrolysis facilitated by myosin's ATPase activity, actin filaments slide past myosin, resulting in sarcomere shortening and muscle contraction.

• The interaction between myosin and actin is key to muscle movement.
• ATP is crucial in powering the contraction cycle.

Myosin's dual role as a structural protein and enzyme is fundamental in ensuring efficient energy use and muscle contraction process, thus paving the way for coordinated muscle activities needed for physical tasks.