Hand-over-hand model

Definition

The hand-over-hand model describes a mechanism of movement where one molecular motor protein binds to a filament and pulls another motor protein along, effectively resembling a relay system. This model is essential for understanding how molecular motors like myosin, kinesin, and dynein transport cellular cargo along cytoskeletal filaments in a coordinated manner.

5 Must Know Facts For Your Next Test

1. In the hand-over-hand model, two motor proteins alternate their binding and unbinding to the filament, allowing for continuous movement.
2. Kinesin typically moves towards the plus end of microtubules, while dynein moves towards the minus end, demonstrating directional transport using the hand-over-hand mechanism.
3. The efficiency of cargo transport increases significantly with the hand-over-hand model due to overlapping interactions between motors and filaments.
4. Myosin operates similarly on actin filaments, using ATP hydrolysis to power its movement in a hand-over-hand fashion.
5. This model helps explain how cells maintain intracellular transport processes essential for functions like cell division, signaling, and maintaining organelle distribution.

Review Questions

• How does the hand-over-hand model enhance the efficiency of molecular motors in intracellular transport?
  • The hand-over-hand model enhances efficiency by allowing two motor proteins to bind and unbind in a coordinated manner as they move along the cytoskeletal filaments. This overlapping action means that while one motor is pulling cargo forward, the other can prepare for the next step without losing momentum. As a result, this model enables continuous movement and reduces the likelihood of cargo detachment during transport.
• Compare and contrast the roles of myosin, kinesin, and dynein in relation to the hand-over-hand model.
  • Myosin, kinesin, and dynein all utilize the hand-over-hand model but operate on different types of filaments with distinct directional movements. Myosin moves along actin filaments towards the plus end, primarily involved in muscle contraction and cellular movements. Kinesin also moves towards the plus end of microtubules, transporting organelles and vesicles away from the cell body. In contrast, dynein moves towards the minus end, playing a crucial role in retrograde transport. Each motor type utilizes this model to effectively navigate their respective tracks.
• Evaluate the implications of the hand-over-hand model for understanding diseases related to dysfunctions in molecular motors.
  • Understanding the hand-over-hand model has significant implications for studying diseases caused by dysfunctions in molecular motors, such as neurodegenerative diseases. If these motors fail to transport cargo correctly due to mutations or malfunctions, it can lead to cellular imbalances and disruptions in vital processes like signaling and metabolism. For example, in conditions like Alzheimer’s disease, impaired axonal transport by kinesin or dynein can contribute to neuronal degeneration. Therefore, insights from this model can help develop targeted therapies aimed at restoring proper motor function or compensating for their loss.

Related terms

Molecular motors: Proteins that convert chemical energy into mechanical work to facilitate movement within cells.

Cytoskeleton: A network of fibers that provide structural support, shape, and organization to cells, serving as tracks for molecular motors.

ATP hydrolysis: The process by which ATP is broken down to release energy, powering the movements of molecular motors.