Flagella : Structure, Functions, Examples

Flagella : Structure, Functions, Examples


At this time, ybstudy.com will discuss the topic of Flagella structure & Function with Example. In this article we will explore flagella, which are structures used by bacteria for motility. We will also examine the main characteristics of this particular structure.

Flagella (singular: flagellum) are long, thin, complementary whips attached to bacterial cells that allow bacterial movement (motility). Bacterial cells generally have a diameter of between 0.1 micron and 50 micron, but on average around 2 micron. Flagella can be several times longer than cells, averaging 10 microns long. Some bacteria have only a single flagellum that protrudes from one end of the cell, while others have many flagella that surround the entire cell.

Flagella : Structure, Functions, Examples

What is Flagella ?

A flagellum is a projection of cells in the form of a whip that participates in the locomotion of single-celled organisms and in the movement of various substances in more complex organisms.

Flagella are found in eukaryotic and prokaryotic strains. Prokaryotic flagella are simple elements formed by a single microtubule composed of flagellin subunits configured helically, forming a hollow nucleus. In eukaryotes, the configuration is nine pairs of tubulin microtubules and two pairs located in the central region. One of the typical examples of flagella is the extension of sperm, which gives them mobility and allows fertilization of the egg.

Cilia, another type of cell extension, have a structure and function similar to that of flagella, but should not be confused with them. They are much shorter and move differently.


Flagella of prokaryotes

In bacteria, flagella is a helix filament whose dimensions range from 3 to 12 microns in length and 12 to 30 nanometers in diameter. They are simpler than the same elements in eukaryotes.

Structure
Structurally, bacterial flagella consists of a molecular property of a protein called flagellin. Flagellins are immunogenic and represent a group of antigens called "H antigens" that are specific to each species or strain. It is configured in a cylindrical way, with a hollow center.

In this flagella, we can distinguish three main parts: the outer and long filaments, the hook located at the end of the filament and the basal body attached to the hook. The basal body shares features with secretory tools for virulence factors. These similarities may indicate that these two systems were inherited from a common ancestor.

Welding
Depending on the location of the flagellum, bacteria are classified into different categories. If the flagellum is located at the cell pole as a single pole structure at one end it is monotric and if it occurs at both ends it is amphitric.

Flagelum is also available as a "feather" on one or both sides of the cell. The latter case occurs when cells have many flagella that are spread homogeneously across the surface, and are called peritric.

Each of these types of whipping also shows variations in the type of movement performed by the whipping. On the cell surface, bacteria also have other types of projections. One is the faucet, this is more rigid than disaster and there are two types: short and abundant, and long involved in sexual intercourse.

Movement
Bacterial propulsion or rotation of bacteria is an energy product derived from proton-motor power and not directly from ATP.

The bacterial flagella is characterized by not rotating at a fixed speed. This parameter will depend on the amount of energy produced by the cell at a given time. These bacteria are capable of not only modulating speed, but also changing direction and movement of flagels.

When bacteria target a specific area, it is possible that the bacteria are attracted to the stimulus. These movements are known as taxis and disasters allow the body to move to the desired location.


Flagella of eukaryotes

Like prokaryotic organisms, eukaryotes show a series of elongations on the membrane surface. Eukaryotic flagella is made of microtubules and is a long projection involved in movement and movement. Furthermore, in eukaryotic cells there may be a series of extras that should not be confused with flagella. Microvilli are plasma membrane connections involved in the absorption, secretion, and adhesion of substances. It is also related to movement.

Structure
The structure of eukaryotic flagella is called axoneme: a configuration consisting of microtubules and other protein classes. The microtubulus is configured in a pattern called "9 + 2", indicating that there is a pair of microtubulus centers surrounded by 9 outer pairs.

While this definition is very popular in literature, it can lead to errors, as only one pair is located in the middle - and not two.

Microtubulus structure
Microtubules are protein elements made from tubulin. There are two forms of this molecule: alpha and beta tubulin. These are grouped together to form a dimer, which will form a microtubulous unit. Units polymerize and merge laterally.

There is a difference between the number of microtubulus-owned protofilaments located around the central pair. One is known as tubule A or complete because it has 13 protofilaments, in contrast to tubule B, which has only 10 to 11 filaments.

Dynein and nexin
Each microtubulus, attached at its negative end to a structure known as the basal body or kinetosome, is similar in structure to the center of the centrosome with nine triplets of microtubules.

The dynein protein, which is very important in eukaryotic flagellar movement (ATPase), is connected by two arms to each A tube. Nexin is another important protein in the composition of flagellum. This is responsible for combining nine pairs of outer microtubules.

Movement
Eukaryotic flagella movement is driven by dynein protein activity. This protein, along with kinesin, is the most important motor element that accompanies microtubules. They "walk" in the microtubules.

Movement occurs when there is a transfer or slip of the outer microtubular pair. Dynein is connected to both type A and type B tubules. Specifically, the base is connected to A and the head is associated with B. Nexin also plays a role in movement. There are several studies responsible for explaining the specific role of dynein in flagel movement.

Flagella : Structure & Functions


The difference between prokaryotic and eukaryotic flagella

Dimensions
The flagella in the prokaryotic lineage is smaller, 12 um in length and an average diameter of 20. Eukaryotic flagella length can exceed 200 um and its diameter approaches 0.5 um.

Structure configuration
One of the great features of eukaryotic flagella is the 9 + 0 microtubulous organization and the 9 + 2 fiber configuration. The prokaryotic organisms lack this organization. Prokaryotic flagella does not cover the plasma membrane, as do eukaryotes.

The composition of the prokaryotic flagella is simple and includes only the flagellin protein molecule. The composition of eukaryotic flagella is more complex, and consists of tubulin, dynein, nexin, and a set of additional proteins - in addition to presenting other large biomolecules such as carbohydrates, lipids, and nucleotides.

Energy
The prokaryotic flagellar energy source is not provided by the membrane-bound ATPase protein, but by the proton motif strength. Eukaryotic flagella has the protein ATPase: dynein.


Similarities in flagella with cilia

Role in movement
Confusion between cilia and flagella is common. Both are cytoplasmic connections that resemble hair and are located on the cell surface. Functionally, both cilia and flagella are projections that facilitate cell movement.

Structure
Both originate from the basal body and have a very similar ultra structure. Similarly, the chemical composition of the two projections is very similar.


Differences in Cilli & Flagella

Long
An important difference between the two structures relates to length: while the cilia are short projections (length between 5 and 20 um), the flagella is much longer and can reach a length greater than 200 um, almost 10 times longer. of cilia.

Quantity
When cells have cilia, they generally occur in large numbers. In contrast to cells that have flagella, which generally have one or two.

Movement
Furthermore, each structure has a strange movement. Silia moves in a strong, wavy flagella, similar to a whip. The movement of each cilium in the cell is independent, while the movement of the flagella is coordinated. The cilia are anchored to the corrugated membrane and the flagella is not.

Complexity
There is a strange difference between the complexity of cilia and flagella in each structure. Chile is a complex projection as a whole, while the complexity of the flagellum is limited to the base, where the rotating motor is located.

Function
Regarding its function, cilia are involved in the movement of matter in a certain direction and flagella is only related to movement. In animals, the main function of the cilia is the mobilization of fluid, mucus or other substances on the surface.


How do bacteria use flagella to find food?

Receptors on the surface of bacteria can detect nutrients in the environment. When the cell is close to the source of nutrition, with a high concentration of nutrients. Further from the source it reduces the concentration of nutrients, resulting in a gradient. This bacterium is able to detect this gradient, orient its body towards the source and rotate the flagella to swim towards nutrition. Movement in response to chemical gradients is called chemotaxis (chemo means chemistry and booth means movement).

If the swimming bacteria encounter a decrease in the concentration of nutrients, it will stop by slowing down the flagella, turning in one place to reorient itself and continuing to swim in different directions. By testing multiple pathways, bacteria can determine the direction of the gradient and orientation to move toward a source of nutrition.

It is important to note that the opposite may happen. If the bacteria detect toxic chemicals, it will spin and move away from the source of the poison, lowering the concentration gradient.


Examples of flagella bacteria

1. Escherichia coli (E. coli) is a classic example of the flagella bacteria. E. coli is a common cause of urinary tract infections. The flagella allow bacteria to move up the urethra into the bladder. Once in the bladder, E. coli can colonize and cause infection.

2. Bacillus cereus is another type of bacterial flagellum. This bacterium is a common cause of food poisoning in buffet restaurants. The presence of flagella allows bacteria to form biofilms and spread on the glass surface serving the dish.

Flagell, Faster than cheetahs
Still, do you think a bacterial cell, supported by flagella, is faster than a cheetah? In real numbers, cheetahs can run around 110 km / hour. Bacteria can only reach speeds of 0.00017 km / hour. Based on pure speed, this race isn't even close, but let's adjust for the big size difference. At 110 km / h, cheetahs can move about 25 bodies every 1 second. Bacteria, at 0.00017 km / h, can move 60 cell lengths per second! Which is pretty impressive for a single cell without muscle or bone.


Frequently Asked Questions About Flagella


What is the role of flagella?
Answer : A flagellate may have one or several flagella. The main function of a flagellum is locomotion, but it also usually functions as a sensory organelle, being sensitive to chemicals and temperatures outside the cell.


What is a Flagella made of?
Answer : Flagella are composed of subunits of a low molecular weight protein, flagellin (20 to 40 kDa), organized helically. The filamentous part of the flagellum extends outside the bacterial surface and is anchored to the bacteria by its basal body.


What are the types of flagella?
Answer : Types and examples of flagella

  1. Monotrophic. - Unique polar scourge. - Example: Vibrio cholerae.
  2. Amphitrichous. - Unique scourge on both sides. - Example: Alkaligens faecalis.
  3. Lophotrichous. - Tufts of flagella on one or both sides. Report this ad.
  4. Peritrichous. - Numerous gullies throughout the bacterial body.



How are the scourges?
Answer : A flagellum is a whip-like structure that allows a cell to move. Although all three types of flagella are used for locomotion, they are structurally very different. The eukaryotic flagellum is a long, rod-shaped structure, surrounded by an extension of the cell membrane like a sheath.


Where are flagella found in the human body?
Answer : Flagella are usually found at one end of the cell and, although they may be sensitive to temperature or certain substances, they are used mainly for cell movement. The cilia have several possible sensory functions, especially when they are part of the nerve cells, and may not move.


Where are flagella found?
Answer : Flagella are filamentous protein structures found in bacteria, archaea and eukaryotes, although they are more commonly found in bacteria. They are normally used to propel a cell through liquid (ie, bacteria and sperm). However, scourges have many other specialized functions


Flagella of human sperm?
Answer : The moving tail of a sperm is a long flagellum, whose central axoneme emanates from a basal body located just after the nucleus


Do females have flagella?
Answer : The only human cells that have flagella are gamete cells - the sperm cells. There are also cilia found in the female reproductive system, where they can also help sperm cells to move towards the egg.


What causes flagella to move?
Answer : Dinein molecules use energy from adenosine triphosphate (ATP), an energy storage molecule, to produce flexion movement in flagella. The dinein molecules cause the flagella to fold by moving the microtubules up and down against each other.


What is the difference between flagella and Cilli?
Answer : Cilia and flagella are structurally similar cellular organelles, but differentiated based on their function and / or length. The lashes are short and there are usually many (hundreds) of lashes per cell. On the other hand, flagella are longer and there are fewer flagella per cell (usually one to eight).


What would happen if there were no Flagella?
Answer : The whip movement produced by the flagella helps to move the cell and its substances. Without flagella, cells would be unable to move, unable to remove substances from their surface. I wouldn't be able to swim towards sunlight or other food.


What is the basic structure of flagella?
Answer : A bacterial flagellum has three basic parts: a filament, a hook and a basal body.


What is faster cilli or flagella?
Answer : Cilia are present in organisms such as paramecium, while flagella can be found in bacteria and sperm. The lashes are shorter and more numerous than the flagella. Cilia and flagella are the most common organelles for locomotion in single-celled organisms. organisms with Flagella can move more quickly and efficiently.


Who discovered lashes and flagella?
Answer : Anthony van Leeuwenhoek
Cilia are the oldest known cell organelle, first described in 1675 by Anthony van Leeuwenhoek in protozoa.