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#axoneme

4 public questions tagged with this topic.

Fertilization in mammals-l

Main structural component of sperm flagellum:

Mammalian sperm flagellum core structure comprises microtubule-based axoneme anchored at basal body in neck region extending through midpiece and principal piece. Axoneme follows canonical 9+2 arrangement of nine doublet microtubules surrounding central pair, with outer dynein arms hydrolyzing ATP generating sliding between doublets converted to bending by radial spokes and nexin links. Accessory outer dense fibers and fibrous sheath provide elasticity. Microtubule dynamics drive progressive and hyperactivated motility; defects in axonemal components cause immotile cilia syndromes, primary ciliary dyskinesia, infertility due to impaired propulsion and flagellar function and reduced fertilization rates.

Ref: Fawcett, The Cell, 2nd ed., Chapter 15: 9+2 microtubule axoneme – dynein-driven motility of sperm flagellum.

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Cytoskeleton

In cilia, what keeps the doublet microtubules from sliding past each other completely?

Motile cilia contain nine plus two axoneme where outer doublets composed of A and B tubules slide relative to each other when axonemal dynein arms anchored on A tubule bind and walk toward minus end of neighboring B tubule, activated in coordinated wave from base to tip. Unrestrained sliding would cause doublets to telescopically extend apart, disrupting structure. Restraint provided by nexin links now recognized as nexin-dynein regulatory complex, elastic proteinaceous bridges composed of DRC1-4 and associated proteins connecting adjacent doublets circumferentially every ninety six nanometers. They limit sliding amplitude to about sixty to seventy nanometers per beat cycle and store elastic energy that recoils to produce bending. Additional resistance from radial spokes transmitting signals from central pair regulates dynein activity. Electron tomography shows N-DRC as hook-like structures. Protease digestion generating sliding disintegration assay causes ATP-induced complete doublet separation, confirming structural role. Kinesin does not reside in axoneme, actin absent, phosphorylation tunes waveform not tethering.

Ref: Porter & Sale J Cell Biol; nexin-DRC elastic links limit sliding, convert sliding to ciliary bending.

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Eukaryotic Cell - Cell Wall and Cell Membrane - Fluid Mosaic Model

Consider the following relationships within the axoneme of a eukaryotic cilium: I. The two central microtubules are conn

The central pair is connected by bridges and enclosed by a central sheath. Nine radial spokes extend towards the peripheral doublets, and the peripheral doublets are also interconnected by linkers. These relationships accompany the 9+2 axonemal arrangement.

Ref: NCERT Class 11 Biology Chapter 8: Cell: The Unit of Life Eukaryotic Cell - Cell Wall and Cell Membrane - Fluid Mosaic Model

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