Architecture of the bacterial flagellum: Which of the following are the major structural components of a bacterial flagellum?

Introduction / Context:
The bacterial flagellum is a rotary nanomachine that enables swimming motility. Understanding its modular architecture is essential for appreciating how rotation is transmitted from the motor to the helical propeller and how direction changes govern runs and tumbles during chemotaxis.

Given Data / Assumptions:

• The question lists three candidate parts.
• We need to determine whether each is part of the flagellum core.
• We focus on the classic Gram-negative model, which also generalizes to many Gram-positives with differences in rings.

Concept / Approach:

The basal body houses the rotary motor and rings that span the membranes and cell wall. The hook functions as a flexible universal joint coupling the motor to the filament. The filament is the long, helical propeller composed mainly of flagellin. Together, these elements convert ion motive force into rotation and thrust to propel the cell through liquid environments.

Step-by-Step Solution:

Verification / Alternative check:

Mutations eliminating any single module abolish motility, confirming functional necessity. Electron cryotomography images clearly resolve these parts and their spatial arrangement.

Why Other Options Are Wrong:

Picking any single element alone ignores the integrated machine.

Excluding any component is inconsistent with established structural and genetic data.

Common Pitfalls:

Confusing pili with flagella; pili do not rotate and are used for adhesion or DNA transfer. Also, mixing up Gram-negative ring composition with Gram-positive architecture does not change the three-module concept.

Final Answer:

All of these