Question

If a motor protein was held in place and a cytoskeletal filament was free to move, what type of motion would occur when the motor protein was active? a. The motor protein would "walk" along the filament. b. The filament would move. c. The filament would bend. d. all of the above e. Only b and c would happen.

Short answer

The correct answer is 'Option b: The filament would move.'

Step-by-step solution

Understanding the relationship of motor proteins and cytoskeletal filaments

Motor proteins are molecules that are able to move along the surface of a suitable substrate. They convert chemical energy into mechanical work by the hydrolysis of ATP. These proteins 'walk' along the filament to carry out their function in the cell.

Considere the reverse scenario

In this case, rather than the motor protein moving along the filament, the motor protein is held stationary, and the filament is free to move.

Reflection about the consequences

By considering the motor protein as stationary but active, the chemical energy from hydrolysis of ATP would be transferred to the filament and cause it to move instead.

Choose the correct alternative

Given that understanding, the answer should be the one that represents the filament moving.

Key concepts

Cytoskeletal Filaments

Cytoskeletal filaments are an essential component of the cell's infrastructure. They form a network that provides structural support to the cell, much like the framework of a building. This network is made up of three main types of filaments: microtubules, actin filaments, and intermediate filaments.
While each type has specific functions, their main role is to maintain the cell's shape, offer support, and facilitate cellular movement.

• **Microtubules**: These are the thickest filaments and are involved in intracellular transport and separation of chromosomes during cell division.
• **Actin Filaments**: Also known as microfilaments, they are the thinnest and contribute to cell movement and contraction during cell division.
• **Intermediate Filaments**: These offer tensile strength, helping the cell withstand mechanical stress.

The interaction of motor proteins with these filaments is vital for many cellular processes. Motor proteins can "walk" along these filaments to perform vital functions like transport of cellular cargo and chromosome separation.
Understanding how these filaments interact with motor proteins helps explain how cellular movement and organization occur.

ATP Hydrolysis

ATP hydrolysis is a chemical reaction that involves the breakdown of ATP (adenosine triphosphate) to ADP (adenosine diphosphate) and an inorganic phosphate. This reaction releases energy that the cell can use to power various functions, including muscle contraction and motor protein activities.
The equation for ATP hydrolysis is: \[ATP + H_2O \rightarrow ADP + P_i + energy\]This process is essential for motor proteins, as they need energy to move along cytoskeletal filaments.
When a motor protein binds ATP, it undergoes a conformational change that enables movement. As ATP is hydrolyzed, the energy released permits the motor protein to "step" forward along the filament, facilitating functions such as intracellular transport.
This cycle of ATP binding, hydrolysis, and release of its products is central to the ability of motor proteins to convert chemical energy into mechanical work. Without ATP hydrolysis, motor proteins would lack the energy needed to perform their functions effectively.

Mechanical Work

Mechanical work refers to any process that involves the transfer of energy to an object, causing it to move. In a cellular context, motor proteins perform mechanical work by using the energy from ATP hydrolysis to move along cytoskeletal filaments. This movement can take several forms:

• **Transport of Cellular Cargo**: Motor proteins, like kinesins and dyneins, transport organelles and vesicles along the filaments to their necessary location within the cell.
• **Muscle Contraction**: Myosin interacts with actin filaments to contract muscle fibers.
• **Cell Division**: During mitosis, motor proteins play a role in separating chromosomes.

In the exercise given, when a motor protein is held in place and the cytoskeletal filament is free to move, the energy from ATP hydrolysis is transferred to the filament causing it to move. This demonstrates the conversion of chemical energy into mechanical work within the cell.
Mechanical work is crucial for maintaining cellular organization and enabling vital biological processes.