Cytoskeleton Motors Flashcards
(21 cards)
What are motor proteins?
Mechanochemical enzymes that convert chemical energy (ATP hydrolysis) into mechanical movement
What are the key roles of myosins?
Organelle transport.
Muscle contraction.
Cell migration
How does myosin move along actin filaments?
ATP hydrolysis causes conformational changes, enabling the myosin head to “walk” along actin.
What is the five step cycle in the movement of actin filametns?
1️ATP binding → Myosin releases actin.
2️ ATP hydrolysis → Myosin “cocked” state, storing elastic energy.
3️ Actin binding → Myosin attaches to actin filament.
4️ Power stroke → Pi release triggers forceful actin movement.
5️ ADP release → Myosin remains bound until ATP binds again.
Why does myosin cause rigor mortis in death?
Without ATP, myosin heads remain tightly bound to actin, causing muscle stiffness
What is the sarcomere?
The contractile unit of muscle fibers, composed of actin & myosin filaments.
What are the key regions in a sarcomere?
Z-disk: Anchors (+)-end actin filaments.
I-band: Actin filaments not overlapped with myosin.
A-band: Myosin filaments interdigitate with actin.
How does muscle contraction occur?
Myosin walks toward the (+)-end of actin filaments.
Z-disks are pulled inward, shortening the sarcomere.
Each sarcomere contracts equivalently, driving whole muscle fibre contraction.
What is the role of tropomyosin (TM) & troponin (TN)?
Tropomyosin blocks myosin-binding sites on actin.
Troponin controls tropomyosin position based on Ca²⁺ concentration.
What medical conditions are linked to TN & TM mutations?
Cardiomyopathies (heart muscle disorders)
How are heart attacks diagnosed using troponin?
Cardiac ischemia (low oxygen) → heart cell death → release of troponin into the bloodstream.
Elevated cardiac-specific troponin levels indicate heart attack severity.
What is kinesin?
A microtubule-based motor protein that uses ATP hydrolysis to move toward the (+) end of microtubules
How many kinesin families exist?
14 distinct families, with 45 kinesin genes in humans
How does Kinesin-1 move cargo?
ATP binding causes conformational changes.
Kinesin “walks” down microtubules in a hand-over-hand fashion.
Cargo is bound to kinesin’s C-terminal domain.
How do dyneins differ from kinesins?
Dyneins move toward the (−) end of microtubules, opposite kinesins.
Composed of 1–3 heavy chains, with ATPase motor domains.
Dynein complex is large (1.5 megaDaltons).
What are the two families of dyneins?
1️Cytoplasmic Dyneins → Transport organelles & vesicles, position nucleus, and assist mitotic spindle formation.
2️ Axonemal Dyneins → Power cilia & flagella beating.
How does dynein move?
ATP binding detaches dynein from microtubules.
ATP hydrolysis causes attachment & movement.
Release of ADP + Pi triggers the power stroke, shifting microtubule position by 8nm.
How does dynein interact with cargo?
Dynein binds cargo via the Dynactin complex, which includes:
Arp1 filament (actin-like structure)
Accessory proteins for specific cargo recognition
- BicD protein links dynein to dynactin, ensuring efficient cargo transport.
How do microtubules regulate melanosome movement in fish pigment cells?
Kinesins disperse melanosomes toward the (+)-end.
Dyneins aggregate melanosomes toward the (-)-end.
Controlled by cyclic AMP (cAMP) → High cAMP = dispersal, Low cAMP = aggregation.
How do kinesins & dyneins coordinate transport?
Organelles & vesicles use both kinesin & dynein for bidirectional movement.
Dynein moves cargo inward toward the nucleus (−).
Kinesin moves cargo outward to the periphery (+).
