السلام عليكم ورحمة الله : تحية طيبة
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1 : كيف تفرق تشريحيا ومورفولوجيا مابين السوط الخلوي عند حقيقات النواة وغير حقيقات النواة؟
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السوط عند غير حقيقيات النواة مكون من انيبيب أجوف (20 نانوميتر ) لولبي الشكل مكون من بروتين الفلاجللين
Bacterial flagellum
The filament is composed of the protein flagellin and is a hollow tube 20 nanometers thick. It is helical, and has a sharp bend just outside the outer membrane called the "hook" which allows the helix to point directly away from the cell. A shaft runs between the hook and the basal structure, passing through protein rings in the cell's membranes that act as bearings. Gram-positive organisms have 2 rings, one in the cell wall and one in the cell membrane. Gram-negative organisms have 4 rings, 2 in the cell wall and 2 in the cell membrane.
The bacterial flagellum is driven by a rotary engine composed of protein, located at the flagellum's anchor point on the inner cell membrane. The engine is powered by proton motive force, i.e., by the flow of protons across the bacterial cell membrane due to a concentration gradient set up by the cell's metabolism (in Vibrio species the motor is a sodium ion pump, rather than a proton pump). The rotor transports protons across the membrane, and is turned in the process. The rotor by itself can operate at 6,000 to 17,000 revolutions per minute (rpm), but with a filament attached usually only reaches 200 to 1000 rpm.
The components of the flagellum are capable of spontaneous assembly in bacterial membranes. Both the basal structure and the filament have a hollow core, through which the component proteins of the flagellum are able to move into their respective positions. The basal structure has many traits in common with some types of secretory pore which have a hollow rod-like "plug" in their centers extending out through the cell wall, and it is thought that bacterial flagella may have evolved from such pores.
Different species of bacteria have different numbers and arrangements of flagella. Monotrichous bacteria have a single flagellum. Lophotrichous bacteria have multiple flagella located at the same spot on the bacteria's surface which act in concert to drive the bacteria in a single direction. Amphitrichous bacteria have a single flagellum each on two opposite ends (only one end's flagellum operates at a time, allowing the bacteria to reverse course rapidly by switching which flagellum is active). Peritrichous bacteria have flagella projecting in all directions.
Some species of bacteria (those of Spirochete body form) have internal flagella that lie between their inner and outer membranes, the rotation of which causes the entire bacterium to corkscrew through its medium.
Anticlockwise rotation of monotrichous polar flagella thrusts the cell forward with the flagellum trailing behind. Periodically the direction of rotation is briefly reversed, causing what is known as a "tumble", and results in reorientation of the cell
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السوط في حقيقيات النواة يتبع النظام 9+2 أي انه يتكون من 9 انيبات دقيقة مزدوجة على محيط السوط واثنان مفردان في وسط السوط .
Eukaryotic flagellum (similar to the cilium)
The eukaryotic flagellum is completely different from the prokaryote flagella in structure and in evolutionary origin. The only thing that the bacterial, archaeal, and eukaryotic flagella have in common is that they stick outside of the cell and wiggle to produce propulsion.
A eukaryotic flagellum is a bundle of nine fused pairs of microtubules called "doublets" surrounding two central single microtubules (the so-called 9+2 structure; also called the "axoneme"). At the base of a eukaryotic flagellum is a microtubule organizing center about 500 nanometers long, called the basal body or kinetosome. The flagellum is encased within the cell's plasma membrane, so that the interior of the flagellum is accessible to the cell's cytoplasm. This is necessary because the flagellum's flexing is driven by the protein dynein bridging the microtubules all along its length and forcing them to slide relative to each other, and ATP must be transported to them for them to function.
For information on biologists' ideas about how the various flagella may have evolved, see evolution of flagella.
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