Flagellum

Flagella (Latin flagellum ) or flagella are thread-like structure on the surface of individual cells, which serve to locomotion. You are in prokaryotes (living without a nucleus ) and eukaryotes ( organisms with nuclei ) fundamentally different in structure and function:

• The flagella of prokaryotes are coiled protein fibers outside the cell membrane that are not actively deform, be transferred to her anchored in the cell end by a motor in rotation and in this way - exert a push or train - similar to a propeller.
• The flagella of eukaryotes, however, are filamentous, enclosed by the cell membrane invaginations of the cell, inside which a bundle of microtubules and is cause by active shape-changing movement.

With the two sometimes used synonymously names flagellum and flagellum two completely separate organelles are called. To the nomenclature to reflect differences in the structure and function of the various pro-and Eukaryotengeißeln, following Language is a German-speaking authors have proposed that "the scourges of eukaryotic cells have a very uniform structure. [ ... ] The term ' flagellum ' is quite different from the organized movement of organelles prokaryotes reserved. "

In the present article, this unique assignment of the terms " flagellum " and " scourge " largely considered ( difficulties arise eg " flagella ", see below). Should be noted, however, that in other current textbooks, this distinction is not made.

• 2.1 Structure
• 2.2 Motion manner
• 2.3 Variations Begeißelungstypen

The flagella of prokaryotes

Construction

Bacterial flagella are extracellular, helical threads ( " filaments "), which are anchored to a "hook " having a motor complex in the cell membrane (or membranes ) and the cell wall. The flagella including hook and motor complex consisting entirely of proteins. The diameter of the filaments is at most flagella about 15-20 nm and they are hollow. Because of their small diameter, they are not only with dark-field microscopy and electron microscopy to visualize with normal light microscopy, however, there are special staining methods, by which they are as much thickened that they are visible by light microscopy.

The structure of the filaments of the protein molecules ( flagellin ) to be transported through the hollow passage to the outer end of the flagella and grown there. If a sufficiently large stock of flagellin in the cell is present, the construction of a filament can be done very quickly.

The flagella of archaea are functionally similar in construction to that of the bacteria, however, consist of other proteins and a separate motor complex, which is driven by ATP.

Begeißelungstypen

After arrangement and number of flagella different Begeißelungstypen be distinguished ( in order of increasing swimming speed ):

• Holotrich Numerous flagella are uniformly distributed over the entire cell surface and cover the entire surface of the body
• Peritrich: Many flagella are scattered uniformly over the cell surface.
• Polytrich Bipolar: The flagella are available in two opposing groups at the cell poles. (also known as amphitrich ).
• Polytrich monopolar: The flagella are in a group at one of the cell poles (also referred to as lophotrich ).
• Monotrich: The cell having a single flagellum.
• Polar: The flagellum or flagella are at one or both poles of the cell.
• Lateral, lateral flagella: flagellar standing sideways, not at the poles of the cell

The lateral flagellum is often associated with high swimming speed, but it has the advantage that the bacteria can more easily squeeze into obstacles such as high viscosity liquids or gaps between solids.

Movement way

The flagella act similar to a propeller through its coiling. The engine is a complex difference in concentration of protons between the two sides of the inner cell membrane into rotational movement of a curved "hook" seated the coiled filament to and follows a similar design principle, such as ATP synthase. The Flagellenmechanik represents the only known real rotating joint in the entire biology represents the rotary frequency is 40-50 Hz

The direction of the motor caused by the flagellar rotation in combination with the winding direction of the flagellar filament determines whether a push or a train is applied to the bacterial body. The direction of the induced by the motor rotation can be reversed in a very short time, so you can change that thrust and train quickly.

In general, the rotational direction of the flagella is so that they push. This means that they are at the monopolar flagellated bacteria at the back end. The bacteria body rotates in the process (slow ) in the opposite direction ( conservation of angular momentum ).

In bipolar flagellated bacteria, the flagella of the two ends rotate in opposite directions. Thus, the flagella of the rear end sliding effect, the flagella of the front end are bent backwards and rotate around the front end of the bacterial body and thus increase the thrust. The rotational direction of the flagella inverted flaps to the filaments, the rear end of the bacterium to the front end and the front end to the rear end, the bacteria swim in the opposite direction.

The flagella peritrichous flagellated bacteria rotate in the same direction, and as a rule so that they push. They combine to form a rearwardly coiled bundle, referred to as " Geißelzopf ", which pushes forward the bacterium. If the rotational direction of the flagella peritrichous flagellated bacteria vice versa, the individual flagella directed radially protruding from the bacterial bodies and their pulling action on the bacterial body stands out on the means by which the bacterium tumbles in random motion in one place.

Reversing the direction of rotation of flagella and the associated change of the movement direction Taxien plays a significant role (see for example chemotaxis).

The flagella of eukaryotes

Construction

The flagella of eukaryotes are thread -like structures that protrude from the body outward into the surrounding medium and are surrounded by the cell membrane and filled with cytoplasm. In its interior are microtubules in a specific arrangement, the so-called 9 × 2 2; Nine double microtubules form a circle, there are two single microtubules in the center of the cross section. The double microtubules consist of a complete microtubule (A tubule ) and incomplete (B- tubule ). At the A- tubules are located in the same vertical distance, about every 20 nm, pairs of protein - poor, who are called dynein arms. This microtubule arrangement is referred to as 9 × 2 2 structure, the entire microtubule bundles as axoneme. This structure is stabilized by different bridge proteins ( esp. Nexin ). At the base of the flagellum, where it merges into the cell body, there is a Basalapparat, which is called Blepharoplast or kinetosome and structurally similar to a centriole. It consists of nine threefold microtubules in a circle ( 9 × 3 structure ), which is transverse to a second, similarly structured 9 × 3 structure. It is often referred to as centriole. At the free end of the eukaryotic flagella are pointed. Their diameter is about 250-300 nm, their length a few microns to over 150 microns.

An illustrative example of flagellated cells produce spermatozoa represents the movement goes in a wave with constant amplitude from the base to the tip of the Scourge.

Together with the cilia refers to the flagella of eukaryotes as Undulipodien.

Movement way

The required for hydrodynamic efficacy shape change comes after the present state of knowledge about through against each other -directed sliding of Doppelfibrillen. The energy to be provided by the Dyneinarmen, by hydrolytic removal of phosphate from ATP. The material forming the dynein arms protein dynein has ATPase activity. The microtubule gliding has a shape change of the scourge result.

The changes in shape of the flagella are different depending on the type scourge. You can in a about the scourge continuous wave ( undulation ) in a plane or in the form of a helix with existing circular to elliptical movements, they can also exist in a scourge strike, the scourge in the curves in one direction and to some extent undermined the medium and suggests extended in the opposite direction and thereby exerting a force. Flagella that move in the last -mentioned manner are called cilia. They are usually shorter than other flagella and are arranged in higher density on the surface of cells and tissues.

The sequence of the flagellum movement can be a continuous movement of the individual, but it may also have at rest an individual movement of the adjacent fluid, or of nearby particles result. Examples of locomotion of the individual: motile ciliates, flagellates, spermatozoa. Examples of movement of the adjacent medium or particles: sessile ciliates, ciliated epithelium in the trachea of animals.

Variations Begeißelungstypen

In some unicellular algae and protozoa are the scourges with many lateral short filaments, called Mastigonemen or fibrillation, occupied and are referred to as Flimmergeißeln. The Mastigonemen can occur in a row ( stichonematisch ) or two rows ( pantonematisch ). Heterokontae have two flagella of unequal length: the shorter of the two is directed in the direction of movement to the rear and is therefore referred to as a trailing flagellum, the longer of the two is a tinsel and directed in the direction of movement forwards.

After the insertion site of the Scourge, a distinction akrokont ( at the front end, Zuggeißel ) pleurokont (lateral) and opisthokont ( rear-end thrust scourge ).