Having a slender, curved, motile growth on certain bacterial cellsproteinThe accessory filaments are called flagella.The length of flagella often exceedsThallusSeveral times.The minimum number is 1-2, and the maximum number is hundreds.
Chinese name
Flagellum
Foreign name
flagellum
Definition
A slender, curved filamentous appendage of proteins with motor function that grows on certain bacterial cells
Length
About 150 microns
Mode of birth
Uniterminal flagellates, terminal arbuscular flagellates, terminal flagellates and peritrichum
ProtoplasmOne or more whips formed by the nerve stretching out of the cell have the functions of movement and feeding.FlagellatesAnd various animals and plantsspermAll have flagella.It is one of the common bacterial organelles.
Some bacteria are attached with slender and wavy filaments, ranging from 1-2 to hundreds.These filaments, called flagella, are responsible for the movement of bacteria.
From someProkaryotic cellandEukaryotic cellA projecting, movable projection on a surface.The flagellum is longer and less in number;ciliaIt has the same structure as the flagellum, but it is shorter and more numerous.The flagellum of bacteria has a completely different structure.
The flagellum is generally about 150 microns long, and the cilia are 5-10micronAnd their diameters are similar, ranging from 0.01 μ m to 0.03 μ m.majorityAnimals and plantsAll sperm have flagella.Sperm and manyprotozoanBoth use flagellum or cilia as the motor.
Most flagellated bacteria areVibrio、bacillusAnd individual cocci.
cell surfaceThe slender flagellate protoplasm protuberances of some bacteria have flagella at one end, both ends or around them.The main types are tail whip type, velvet whip type, etc.Tail whip type: A type of flagellum.Under the electron microscope, there is no trichome (or flagellum) on the flagellum surface.Common in Chlorophyta and CharophytaZoosporeOr the flagellum of sperm, and the sperm of mosses and ferns in higher plants are tail whip flagellum.There are also some algae and lower fungi with a tail whip type flagellum and a velvet whip type flagellum.Antler whip type: A type of flagellum.Under the electron microscope, there are many feathery hairs (or flagella) on the surface of flagella.Common species in gymnophyta and cryptophyta.In dinoflagellates, brown algae and some lower fungi, it is common to have one flagellum type flagellum and the other flagellum type flagellum on the same swimming cell[1]。
Flagella can be found on the surface of cells in various ways, including uniterminal flagellates, terminal arbuscles, terminal flagellates, and peritrichum.
There are three movements of flagella: swimming in liquid, sliding on solid surface, and rotating shuttle in liquid.Bacteria swim by flagella.Flagella are produced from a base point on the cell membrane and pass throughcell wallAnd the slime layer, the length of which can be several times the length of the cell.Most cocci have no flagella, and some bacilli have flagella,SpirillumThey all have flagella.Because the flagellum is very thin, it can only be used with a special dyeing methodoptical microscopeObserved.
type
Announce
edit
Archaellum
Archaea flagellum, which looks like bacterial (or Eubacterial) flagellum on the surface.
In the 1990s, many detailed differences between archaea and bacterial flagella were found, including:
The bacterial flagellum is composed of a flowing H+ion, and the ancient flagellum is almost certainly composed ofadenosineTriphosphoric acid [ATP].
Bacterial cells often have many filaments of flagellum, and ancient flagellum consists of many filaments in a bundle.
Bacterial flagellum
Different kinds of bacteria have different numbers of flagella.Monotrichous bacteria have a single flagellum (e.gVibrio cholerae）。 Lophototrichous bacteria have multiple flagella on the same surface of the bacteria, and act in concert to move the bacteria in a single direction.
In some bacteria, such as selenomonas, flagella are organized exosomes.
Eukaryotic flagellum is completely different from other flagellumprokaryoteFlagella in structure and evolutionary origin.
Flagella can be divided into terminal and peripheral
chemical composition
Announce
edit
Structural pattern of Escherichia coli flagellum root
Protein. Flagellin has strong antigenicity, which can be used to identify and type bacteria.
Structure: flagellum grows from the cell membrane and is free fromBacterial cellOutside, withbasal body 、Uncinate bodyandFilamentous bodyIt consists of three parts.G+bacteria（Gram positive bacteria）The basal body is composed of S and M rings, and G-bacteria（Gram negative bacteria）The basic body is composed of L, P, S and M rings.stayEscherichia coliIn, the L ring is connected to the outer membrane of the cell wall, the P ring is connected to the peptidoglycan layer, the S ring is located in the periplasmic gap, and the M ring is connected to the plasma membrane. The four rings are connected by the central rod.
Motor mechanism
Announce
edit
Cilia and flagella are composed of three main parts: central axis filament, plasma membrane around it and some cytoplasm.From the base of a cilia or flagellumGranaStraight to the top, a bunch ofmicrotubuleAt the bottom of grana, they gather into conical bundles and penetrate into the cytoplasm.
The microtubule arrangement on the cross section of the axial filament is 9+2, that is, there is a pair of microtubules wrapped by the central sheath in the center, and nine groups of microtubules connected by two pairs are surrounded by the peripheryDimer。
Structure image of matrixCentrioleThe same type is 9+0, and its 9 groups of microtubules are alsoTriplet。The microtubules in the cilia or flagella dimer extend from two microtubules in the grana triad.
The movement of flagella and cilia is the result of their local bending and wave pushing from the base to the top.Because of microtubuleDimerIt is speculated that this local bending is caused by the sliding of two adjacent microtubule dyads along the long axis.The energy required for local sliding is periodically generated by ATPhydrolysisProvided.
The structure and chemical composition of bacterial flagella are completely different from those of eukaryotic cells. There is no 9+2 microtubule pattern, but there are 2-5 flagella with a width of 40-50 angstromsMicrofilamentIts protein composition isFlagellin。Except for spirochete, flagella of other bacteria have no plasma membrane coating.Although their basement also goes deep into the particles in the protoplasm, this kind of particles has nothing in common with the grana.BacteriaFlagellationThe energy source of is not ATP, which is believed to come from the cell membraneElectron transfer systemProducedElectrochemical gradient。
Sliding model (Figure 1)
Sliding theory The movement of flagella is determined byaxonemal dynein It is caused by the mutual sliding between the adjacent dimer microtubules mediated by.From aDimerPipe A ofDynein armThe motor structure of is "walking" on the B tube of the adjacent dyad, and the process is shown in Figure 1 on the right.
Sliding model
(1) Pipe ADyneinThe contact between the head and the B tube promotes the binding of dyneinATP hydrolysis, the product is released, and the head angle is changed at the same time.
⑵ New ATP binding makes dynein head separate from B tube
⑶ ATP hydrolysis, the released energy restores the angle of the head
⑷ The dynein with hydrolysate is active, while the dynein on the other side is inactive. The alternate sliding of dynein between adjacent dimers to both sides will cause the flagellum to bend in different directions.
Function application
Announce
edit
Flagella can help bacteria move.Flagellates can move freely and quickly in liquid environment.
1. Chemical tendency movement helps bacteria move towards nutrients and escape from harmful substances.
2. It is related to bacterial pathogenicity.
3. Identification and classification of bacteria[2]。
