F-Actin Is Not a Straight Polymer but Can Be Considered

question 30

Multiple Choice

F-actin is not a straight polymer but can be considered a double-helical assembly. The two protofilaments twist around each other and cross over approximately every 13 actin subunits, and the subunits in each protofilament are repeated every 2.8 nm along the helix. F-actin is almost 8 nm wide. Different myosin motors have different "step lengths" on actin depending on their function. Which of the following step lengths would you expect to belong to a processive myosin motor that carries large cellular cargoes such as endocytic vesicles?

• A) About 2.8 nm
• B) About 8 nm
• C) About 13 nm
• D) About 27 nm
• E) About 36 nm

---

Definitions:

Thin Lava Flows

Layers of lava that spread out over large areas and cool to form relatively thin sheets of rock.

Lava Fountain

A volcanic phenomenon in which molten lava is forcefully ejected into the air from a vent or crack in the Earth's surface.

Pyroclastic Flow

A rapid flow of hot gases and volcanic debris that descends along a volcano's slopes when there's a violent eruption.

Lava Dome

A roughly circular mound-shaped protrusion resulting from the slow extrusion of viscous lava from a volcano.