Molecular Motors and Intracellular Transport

Study Notes

Cell functions likened to a city for easier understanding of transport dynamics.
Workers represent proteins, power plants symbolize mitochondria, and roads are actin fibers and microtubules.
Trucks are analogous to molecular motors: kinesin, dynein, and myosin.
Factories represent ribosomes, and the library symbolizes the genome. Other comparisons include lysosomes as recycling centers, chaperones as police, Golgi apparatus as post offices, and signaling networks as communication systems.

Microtubules (MT) function as freeways, facilitating rapid transport, while actin filaments serve as local streets for slower, more precise movement.
Intracellular traffic can involve dispersion (spreading cargo throughout the cell) and aggregation (retrieving cargo back to the nucleus).

Myosins and kinesins function as motor proteins that transport cargo along actin and microtubule structures.
Myosins are characterized by their ability to bind to actin filaments and move towards their plus ends, using ATP for energy and undergoing conformational changes during the process.

Myosin II, a specific type of myosin, plays a role in vertebrate muscle contraction through its cross-bridge cycling mechanism.

Comprising four polypeptide chains, kinesin includes two heavy chains (with globular head domains and long helical tails) and two light chains that vary depending on the type of cargo being transported.
Kinesin operates primarily in a plus-end directed manner along microtubules.

Dyneins are the largest and fastest molecular motors (14 mm/sec compared to kinesin's 2 mm/sec).
They direct cargo movement toward the cell center, including vesicles and the Golgi apparatus, and function as minus-end directed motors.