Kinesin, Dynein, and Intracellular Transport
Cells use molecular motors such as kinesin and dynein to transport cargo along cytoskeletal tracks.
The Investigative Question
How do molecular motors move cellular cargo to particular locations within a cell?
What We Observe
Large eukaryotic cells cannot rely upon random diffusion to place every component where it is needed. Molecular motors transport vesicles, organelles, proteins, chromosomes, and other cargo along organized cytoskeletal structures.
Scientific Background
Kinesins and dyneins convert chemical energy from ATP into directed movement along microtubules. Motor proteins bind cargo through additional proteins and molecular complexes, allowing different materials to be transported to appropriate cellular locations.
Why It Matters
Intracellular transport demonstrates that cellular organization depends upon more than manufacturing molecules. Cells also require systems that distribute materials in space and time.
What Is Known
The stepping mechanisms, structures, ATP dependence, directionality, and many cargo interactions of kinesin and dynein motors have been characterized experimentally.
What Is Proposed
Evolutionary explanations trace motor-protein families through gene duplication, divergence, specialization, and changes in cargo-binding and regulatory systems.
What Remains Uncertain
Although relationships among modern motor proteins can be reconstructed, the earliest stages by which primitive cytoskeletal transport systems became integrated with cargo recognition and regulation remain less certain.
Key Numbers
Individual molecular motors operate at nanometre scales while transporting cargo over distances that can be enormous relative to the size of the motor itself.
Design Relevance
Directed transport is relevant to design because successful cellular operation requires coordinated relationships among motors, tracks, cargo, energy sources, destinations, and regulatory signals.
Assessment
Molecular motors provide another example of organized cellular machinery. Their existence is not by itself evidence sufficient to establish design, but their origin and integration contribute to the cumulative question of how cellular organization arose.