Kinesin is the molecular motor among the options, as it uses ATP hydrolysis to transport cargo along microtubules.

Question Analysis

The query identifies which option is a molecular motor—proteins that convert ATP energy into mechanical work for cellular movement.

Option Breakdown

• Kinesin: A microtubule-based motor protein with a motor domain that binds microtubules and ATP. It undergoes conformational changes via ATP hydrolysis to “walk” cargo toward the plus end, essential for transport and mitosis.

• Kinetin: A synthetic cytokinin (plant hormone) that promotes cell division; not a protein or motor—involved in growth regulation.​

• Keratin: A fibrous structural protein forming intermediate filaments for mechanical strength in skin, hair, nails—no motor activity.​

• Dynactin: A multi-subunit complex that regulates dynein (another motor) but lacks its own motor domain; acts as an adaptor.​

Answer: Kinesin—the true molecular motor.​

Introduction to Molecular Motors

The molecular motor kinesin powers intracellular transport by moving along microtubules using ATP. Unlike structural proteins or hormones, kinesin exemplifies motor proteins vital for vesicle trafficking and chromosome separation.

Kinesin Mechanism

Kinesin’s motor domain features an ATP-binding site and microtubule-binding loops. ATP hydrolysis triggers conformational shifts, advancing it 8 nm per step in a hand-over-hand motion.

Comparing Options

Kinetin drives plant cell division hormonally, keratin provides cytoskeletal support, and dynactin aids dynein without independent motility. Only kinesin fits the motor definition.​

Biological Importance

In neurons and dividing cells, molecular motor kinesin ensures organelle delivery. Dysfunctions link to diseases like neurodegeneration, highlighting its exam relevance.