Flagella structure

Ill, THE GENETIC CONTROL OF FLAGELLA STRUCTURE IN CHLAMYDOMONAS REINHARDII... 

Class B. Suppressor of tubule mutations. This mutation has no effects on flagella structure when present alone but modifies the expression of certain center tubule mutations. It is discussed more fully in Warr et al. (1966). 

An isolated flagellum will continue to bend actively, indicating that this function is linked to its intrinsic structure. Treatment of cilia from the protozoan Tetra-hymena with the proteolytic enzyme trypsin selectively dissolves the nexin links and radial spokes but leaves unaffected the microtubules and dynein arms. If such a preparation is treated with a small amount of ATP, the loosened microtubule doublets slide against each other and through longitudinal overlap, extend for a distance that is up to nine times the original length of the cilium (Warner and Mitchell, 1981). 

Axons of antennal ORCs project through the antennal nerve to enter the brain at the level of the ipsilateral antennal lobe (AL) of the deutocerebrum (52). ORC axons project from the flagellum to targets in the AL, but axons from antennal mechanosensory neurons bypass the AL and project instead to an "antennal mechanosensory and motor center" in the deutocerebrum posteroventral (with respect to the body axis of the animal) to the AL (52, 58, 64). In moths and certain other insect groups, sex-pheromonal information is processed in a prominent male-specific neuropil structure in each AL called the macroglomerular complex (MGC) (16, 52, 64, 65). 

It is informative to compare these dimensions with those of the smallest structures visible in cells for example, a bacterial flagellum is -13 nm in diameter and a cell membrane -8-10 nm in thickness. Bricks of the size of the 300-residue polypeptide could be used to assemble a bacterial flagellum or a eukaryotic microtubule. Helical polypeptides may extend through cell membranes and project on both sides, while a globular protein of the same chain length may be almost completely embedded in the membrane. 

Flagellum 0.1 x 12,000 nm Protein structure arises from membrane. Responsible for motility... 

The discovery that the flagellum is more complex than first supposed, that it also contains an unpredicted, sophisticated protein-pumping mechanism, and that structures resembling the protein pump can occur independently, briefly set Darwinian hearts aflutter. The innocent optimism was based on Ken Miller s rhetorical redefinition of irreducible complexity, which decreed that parts of IC systems could not have any other function. Since a subset of the flagellum appeared to be part of the TTSS, then that violated Miller s dictum, and cheered some of the more unreflective Darwinists. 

Cilia and flagella are stable microtubule-based structures which project from the plasma membranes of particular eukaryotic cells. The energy-dependent oscillations of these structures can drive material over the surface of a cell or propel the cell along. For example, the whip-like motions of cilia on the cells at the head of the fallopian tube draw newly released ova from the ovaries into and along the oviduct. The snake-like movements of the flagellum on a sperm provide these cells with movement. 

Figure 34.29. Structure of Flagellin. A bacterial flagellum is a helical polymer of the protein flagellin. %...

Figure 34.32. Proton Transport-Coupled Rotation of the Flagellum. (A) MotA-MotB may form a structure having two half-channels. (B) One model for the mechanism of coupling rotation to a proton gradient requires protons to be taken up into the outer half-channel and transferred to the MS ring. The MS ring rotates in a counterclockwise direction, and the protons are released into the inner half-channel. The flagellum is linked to the MS ring and so the flagellum rotates as well.

Flagella - Flagella (singular, flagellum) are hairlike structures that provide a means of locomotion for those bacteria that have them. They can be found at either or both ends of a bacterium or all over its surface. The flagella beat in a propeller-like motion to help the bacterium move toward nutrients away from toxic chemicals or, in the case of the photosynthetic cyanobacteria toward the light. 

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