Flagellum Function in Prokaryotic Cells
A flagellum is a tail-like structure found on cells (bacteria) that help them move around and be more productive. Flagella are composed of proteins, and since they don’t need to separate like organelles, they can work together to propel the cell in many directions.
The flagellum is an organelle of many cell types in the body of microbes. In fact, the flagellum is the most common organelle that has been found in microbial cells. Flagella are long and thin, and they don’t jut out from the cell like a plant or animal cell. They can be found in some microbes on their outer surface, or they can be found inside—for example, the antibiotic-producing bacteria, Streptomyces.
The Importance of Flagella to Prokaryotes Prokaryotes are vital in the ecosystem. There are three types of prokaryotes: bacteria, archaea, and protozoa. These organisms are classified as prokaryotes because they have a cell membrane, ribosomes, a nucleus, and no mitochondria.
Types of Flagellum
Flagella are long, whip-like structures that propel bacteria through their environment.
- Monotrichous: A single flagellum at one end of the organism or the other.
- Lophotrichous: Several flagella on one end of the organism or the other.
- Amphitrichous: A single flagellum on both ends of the organism.
- Peritrichous: Several flagella attached all over the organism.
Monotrichous flagella are found in bacteria and archaea. They have a single, long flagellum that is used for locomotion. The bacterial flagellum rotates around its own axis, while the archaeal one rotates about an axis perpendicular to the cell’s surface.
Lophotrichous bacteria have multiple flagella located at the same spot on the bacterial surfaces, which act in concert to drive the bacteria in a single direction. In many cases, the bases of multiple flagella are surrounded by a specialized region of the cell membrane called the polar organelle.
Amphitrichous flagella have multiple filamentous structures that extend outward from the cell. The thin filaments are arranged asymmetrically on the cell surface, with one or two more prominent structures extending outward. The flagella allow the amoeba to glide, enabling the organism to move towards food sources.
The flagella are also believed to serve a sensory purpose; they can detect changes in direction and in force. For example, when the amoeba moves towards a surface, the flagella spread outwards like probes, suggesting that they can transmit information about objects and surfaces in their immediate environment.
The flagella also play a role in locomotion and may be required for the organism to swim. The flagella can bend and twist when the amoeba moves. The sensory function of these structures is not well understood.
“Pleurostomum libanoticum”‘s flagella are asymmetrical, with a larger, more prominent flagellum located on one side of the body. This seems to be true regardless of whether or not the organism is moving.
An example of an Amphitrichous Flagella bacteria is Proteus.
Peritrichous Flagella are one of the three main types of flagella. The other two are whiplike eukaryotic flagella and bacterial flagellum.
They are short, for they span a small length from base to tip, at the point where they connect with their motor proteins. They possess a central basal body that connects to the cell’s plasma membrane in which they reside. They have a contractile structure connecting the basal body to the tip of the cell. This structure is called the axostyle.
Peritrichous flagella undergo waves of contraction and relaxation, much like cilia and eukaryotic flagella. These contractions cause their tips to move back and forth, making peritrichous flagella useful for bacteria with characteristic gliding motility (e.g., “E. coli”).
This motion also causes the microvilli that line the intestine to beat in synchrony with the flagellum, which is helpful to organisms that reside in environments with little available oxygen as it increases the surface area of the intestines.
These flagella are used for a variety of purposes within their bacterial host. For example, they are often used for transport or motility. The process in which bacteria utilize these flagella to move around is called gliding motility. They can digest certain food sources as well.
Flagellum Function in Prokaryotic Cells
Bacteria have many small structures called flagella that allow them to swim through a liquid environment. These structures are driven by a rotating propeller at the cellular level. The motor that makes the propeller turn is powered by proton gradients, an electrical current that’s constantly generating new protons near the mitochondria, flowing down through the membrane, which creates a concentration gradient. Once the proton gradient is established, enough energy is to propel the bacteria through a liquid environment.
In prokaryotes, the flagellum is an organelle that helps them move. The protein associated with the flagellum is called flagellin. When the flagellum is in the forward position, it can propel the cell in that direction. The bacterium will move in the opposite direction if the flagellum is pointed backward.
Many prokaryotic cells use flagella to move around, which can be found in the single-cell organisms of bacteria. The flagellum is made up of a propeller, and a motor protein called the rotary motor and a filament known as the hook. The filament is used to generate thrust due to its spinning motion while at the same time in contact with other molecules in the fluid.
To function, flagella require help from more complex cells. The flagellum can “push” cells using dynein motor proteins. How the flagellum moves depends on whether it’s powered by a rotary motor (as in the archetypal whip-like bacterial form) or a linear motor (as in many other forms).
The flagellum structure is dynamic, and it changes shape based on the direction and velocity of its motion. For the prokaryotes that form flagella, these changes are significant because they allow them to adapt to different environments.
Flagella can also be used for two other purposes in addition to propulsion. One is chemotaxis, which is when cells move towards chemicals (or away from chemicals) in their surroundings. Another is the ability to move across surfaces that bacteria do not have cell walls.
Flagella function has been studied from many different perspectives—studies of structure, movement, and dynamics often come as a package with RNA interference studies and attention to the flagellum’s chemical machinery.
Scientists have done a lot of research into the three main proteins that make up a flagellum—the components of an HCP called FliH. One of these proteins, FliH, was chosen to be the most studied prokaryotic gene after its discovery by Barbara McClintock in her studies on maize.
Flagella function is essential for microbes that need to move around or for locomotion purposes. Bacteria that lack flagella will die off if they do not have another type of motility system—a flagellum can give them their only chance to move around and stay alive. Without these microbes, the world would be in danger of starvation.
A flagellum is a tail-like structure and therefore has two main parts: an axial part and a basal part with associated components. However, the flagellum is not shaped like a tail. Instead, it is located on the cell surface and shaped like a blade (looking downward). The appearance of the tail can be different for different species.
For example, the tail of Escherichia coli is short and straight, while the tail of Mycoplasma genitalium is long and curved.
The flagellum moves to utilize a rotary motor that forces it to rotate. The assembly of the HCP and its motor proteins is what determines how fast the flagellum can move. Besides using proteins to make motility possible, the flagellum also contains a kind of homing agent to help in natural selection and adaptation.
Flagella are important for prokaryotes. After all, they help them move, which is important for these organisms because most of them live in the water or need to move around searching for food. There are many causes of flagellar dysfunction, but the main one is infection from viruses that do not have protein coats and thus can get into the cell.
It is also possible to stop a bacterium’s flagella by doping it with a very toxic compound that kills off the cell. The compound is used as a poison to kill bacteria that are harmful to humans.
Not all bacteria have flagella, and not all cells with flagella are bacterial. There are flagella on the bacterial endosymbionts of plants, animals, and fungi, and for these organisms they need to move around in search of food or new habitat.
Flagella have been present in human cells for more than 40 years, but the function has only just recently been discovered—by geneticists. Flagella are used by the cells that line the fallopian tubes and give rise to an embryo’s cell cycle. The flagella help facilitate a mitotic spindle, which is what enables embryos to grow.
The prokaryotic flagellar function has been studied in various fields, such as biochemistry, biophysics, and molecular biology. Research in biochemistry has focused on the processes that help to turn flagella into motility. Studies have also been done on how motor proteins work and how they are made.
These studies have shown that all three of these factors are important for making the flagellum work. Research has shown that chemical rearrangements in motor protein structure (called post-transcriptional modifications) change how fast the flagella move.
Much of the research for how prokaryotes move has been done in molecular biology. Scientists have studied the genes that are involved in the flagellum structure and its function, such as FliH. Barbara McClintock discovered FliH after looking into the cause of a genetic mutation that caused brown spots to appear on the leaves of corn.
She discovered that these spots occurred on chromosomes within the nucleus and that a change in the DNA structure caused this. Further research has shown that the genetic mutations in FliH occur across many species of bacteria.
Even though FliH is not as well studied genetically, it is still one of the most important genes to understand prokaryotic motility better.