Final answer:
Most motor proteins, like kinesin and dynein, achieve unidirectional movement through ATP-fueled conformational changes that allow them to 'walk' along cellular structures such as microtubules and actin filaments in only one direction.
Step-by-step explanation:
Motor proteins ensure unidirectional movement through a combination of structural features and biochemical processes. The primary motor proteins, namely kinesin and dynein, walk along microtubules using the free energy from ATP hydrolysis. The irreversible conformational changes in these proteins during the ATP hydrolysis cycle provide unidirectional movement. As ATP binds to the motor protein, it induces a conformational change leading to the 'power stroke' that drives movement. Following this, ATP hydrolysis occurs, and the subsequent release of ADP and inorganic phosphate resets the protein for another cycle.
This mechanism is very similar in the actin-based motor protein, myosin. Bindings of ATP to myosin cause the dissociation from actin, which allows for the cyclic interaction between myosin and actin filaments for movement. Collectively, this ATP-dependent process ensures that motor proteins 'walk' in one direction along their respective filaments or tubules, carrying various cell cargo, such as neurotransmitter vesicles or other organelles. This targeted and directional transport is pivotal for numerous cellular functions, including neurotransmission and muscle contraction.