Question

Select the total number of true statements from the following. 1\. Each myosin (thick) filament is also a polymerized protein. 2\. Many monomeric proteins called meromyosins constitute one thick filament. 3\. Each meromyosin has two important parts, a globular head with a short arm and a tail, the former being called the heavy meromyosin (HMM) and the latter is called the light meromyosin (LMM). 4\. The HMM component, i.e., the head and short arm projects outwards at regular distance and angle from each other from the surface of a polymerized myosin filament and is known as cross arm. 5\. The globular head is an active ATPase enzyme and has binding sites for ATP and active sites for actin. (a) 1 (b) 2 (c) 4 (d) 5

Short answer

The total number of true statements is 5, so the answer is (d) 5.

Step-by-step solution

Analyze each statement individually

Let's check each statement one by one.\n 1. True. Myosin filaments are indeed constructed from polymerized protein.\n 2. True. Myosin filaments are constructed from many monomeric proteins, known as meromyosins.\n 3. True. Each meromyosin does have a globular head with a short arm and a tail, with the respective names provided in the statement.\n 4. True. The HMM component, i.e. the head and short arm, do project outward at regular intervals from the filament, known as cross-arms.\n 5. True. The globular head does contain active sites for both ATP and actin, and is indeed an active ATPase enzyme.

Count the true statements

All five statements are true. So the total number of true statements is 5.

Key concepts

Myosin Filaments

Myosin filaments form the core structure of muscles and play a key role in muscle contraction. These filaments are known as thick filaments and are made up of a large number of protein subunits that create a long, rope-like structure.

Myosin itself is a motor protein that interacts with actin filaments to produce muscle contraction. This interaction is crucial for motions ranging from a simple blink to running a marathon.

During contraction, myosin filaments slide past actin filaments in a process powered by ATP, leading to a shortening of the muscle fiber and, hence, a contraction. It's important to note the polymerized nature of the myosin filament. They are built from smaller parts combining together, which means they are indeed polymerized proteins.

Meromyosin

Meromyosin refers to the components that make up the myosin filament. These components are protein monomers or subunits that attach together to form the complete filament structure.

Each of these monomeric units is referred to as meromyosins and can be classified into two different types based on function and structure:

• Heavy Meromyosin (HMM): This part has a globular head and a short arm. It plays a vital role during muscle contraction because the globular head acts as a cross-bridge that connects to actin filaments.
• Light Meromyosin (LMM): This is essentially the tail portion, which allows for the assembly of the myosin filament itself.

Meromyosins are critical as they are directly involved in the mechanism of contraction and maintain the structural setup of the filament, ensuring they align properly to facilitate consistent contraction.

ATPase Activity

The ATPase activity is crucial in muscle contraction, powering it on a molecular level. The globular head of the heavy meromyosin has ATPase activity, which means it can hydrolyze ATP. This hydrolysis provides the energy necessary for the cross-bridge cycle to occur.

The process goes as follows:

• ATP binds to the head of the myosin, which results in a conformation change.
• The ATP is broken down into ADP and an inorganic phosphate (Pi), a process that releases energy.
• This energy release drives the power stroke, where the myosin head pulls on the actin filament, causing the muscle to contract.
• Once the power stroke is complete, a new ATP molecule binds, causing the myosin head to detach from actin and reset for the next cycle.

Without the ATPase activity of myosin, the muscles would be unable to contract efficiently, highlighting the importance of this enzymatic function.

Protein Polymerization

Protein polymerization is the process by which proteins, like myosin, oligomerize to form larger, complex structures. In muscle fibers, this occurs extensively to create the intricate network necessary for muscle function.

Polymerization occurs when monomeric proteins, meromyosins in this context, bind together in a specific arrangement to form a functional myosin filament. This type of polymerization is crucial for ensuring the structural integrity and alignment of muscle fibers.

Through this process, proteins not only form myosin filaments but also gain unique mechanical properties, which are essential for muscle contraction. The well-organized assembly of myosin in a polymerized state allows for coordinated muscle movement and strength. This aspect of protein science ensures that muscle cells can withstand and respond to various physical demands, from subtle movements to powerful exertions.