Flagellum

Some tiny living things have a little tail.

It looks like a small whip. This tail helps them swim. It moves them through the water. It helps them find food.

Some tails spin like a motor. Other tails bend back and forth. A tiny germ uses its tail to swim in a stomach. It can have one tail or many tails. This tail is a great tool for moving around.

A flagellum is a tiny, hair-like part on a cell.

Its name comes from a word that means "whip." This part helps cells swim through water. It is used by many tiny living things. This includes bacteria, fungi, and even some animal cells.

There are different ways flagella work. Some cells use a rotary motor. This means the tail spins like a propeller. This type is found in bacteria. Other cells use a bending movement. This tail lashes back and forth like a whip. These are called eukaryotic flagella.

In bacteria, the motor is at the base. It uses a flow of protons to get power. Protons are tiny parts of an atom. This motor can spin very fast. Some bacteria can move 60 body lengths in one second. This is very fast for such a small life form. A bacterium named Helicobacter pylori uses its tail to swim in a stomach. It moves to reach the lining of the stomach. This can lead to ulcers.

A flagellum is a tiny, hair-like part that helps cells move.

The name comes from a Latin word meaning "whip." This part lets many living things swim through water. You can find flagella on animal sperm cells and fungal spores. They are also used by many tiny microorganisms. Some bacteria, like Helicobacter pylori, use them to swim through the stomach. This helps them reach the stomach lining.

There are three main types of flagella in the world. These are called bacterial, archaeal, and eukaryotic flagella. They all help with movement, but they work in different ways. Prokaryotic flagella, found in bacteria and archaea, use a rotary movement. This means they spin like a propeller. Eukaryotic flagella use a bending movement. They lash back and forth instead of spinning.

In bacteria, the flagellum works like a tiny machine. It has a rotary motor at its base. This motor is powered by a flow of protons. Protons are tiny parts of an atom that move across the cell membrane. The motor can spin very fast. It can reach speeds between 6,000 and 100,000 rpm. Most bacteria use the motor at speeds between 200 and 1,000 rpm. A protein called FliG acts as a switch to change the direction.

Bacterial flagella are very detailed structures. They are made of a protein called flagellin. The shape is a hollow tube that is 20 nanometers thick. This tube is helical, which means it looks like a screw. A part called a hook helps the filament point away from the cell. In some bacteria, like Escherichia coli, the filament has 11 protofilaments. Other bacteria, like Campylobacter jejuni, only have seven.

Scientists study how these parts evolved over time. Some believe the flagellum evolved from a system used to inject proteins. This is called the type-three secretion system. Other scientists think they might have grown separately. Even though they are complex, flagella are very flexible. Many different proteins can be added or lost, and the cell still moves. This flexibility helps different kinds of life thrive in many places.

A flagellum is a hair-like appendage used by many organisms to achieve motility, or movement. The name comes from the Latin word for "whip," which describes its lashing motion. Flagella are found on various life forms, including animal sperm cells, fungal spores known as zoospores, and many microorganisms.

These structures are vital for survival in many environments. For example, the bacterium Helicobacter pylori uses its flagella to swim through the stomach. This allows it to reach the mucous lining of the epithelium. Once there, it can colonize the area and potentially cause gastritis or ulcers.

Across the three domains of life—Bacteria, Archaea, and Eukaryota—flagella perform the same function. However, they differ greatly in structure and how they move. Prokaryotic flagella, found in bacteria and archaea, use a rotary movement like a propeller. Eukaryotic flagella use a bending movement, lashing back and forth. In eukaryotes, flagella contain microtubules and a protein called dynein to create this bending. Archaea have a structure called an archaellum to distinguish it from bacterial versions. While eukaryotic flagella and cilia are structurally identical, they differ in length and specific function.

The bacterial flagellum is a highly complex machine requiring over 50 different proteins. It consists of a helical filament made of protein subunits called flagellin. This filament is a hollow tube about 20 nanometers thick. A part called the hook allows the filament to point away from the cell. The structure also includes a shaft and a basal body. In gram-negative bacteria, the basal body uses four specific rings: the L, P, M, and S rings.

These rings act like bearings to support the rotating shaft.

Movement in bacteria is driven by a rotary engine called the Mot complex. This engine is located at the anchor point on the inner cell membrane. It is powered by proton-motive force, which is the flow of protons across the membrane. This flow creates a concentration gradient that turns the rotor. The rotor can operate at speeds between 6,000 and 100,000 rpm. However, when the filament is attached, the speed usually drops to 200 to 1,000 rpm.

A protein named FliG acts as a molecular switch to change rotation direction.

Bacteria use these rotations to navigate their environment through a process called a biased random walk. They perform "runs" and "tumbles" to move toward attractants or away from repellents. Counterclockwise rotation acts as a "thruster mode," where the flagella lag behind the body. Clockwise rotation is called "traction mode," where the body follows the flagella. Some bacteria, like Vibrio species, use a sodium ion pump instead of a proton pump. This allows them to achieve remarkable speeds relative to their size. Some bacteria can move at 60 cell lengths per second.

Scientists have long debated how the flagellum evolved. One major theory is that it evolved from the type-three secretion system (TTSS). The TTSS is a structure used by many gram-negative bacteria to inject proteins. Both systems share many similar proteins and a similar number of components. Some researchers suggest they evolved from a common ancestor. Others believe they may have evolved in parallel. Despite arguments that the flagellum is "irreducibly complex," many mutations show the system is actually very flexible. It can lose or gain proteins and still function effectively.

Flagellar arrangements also vary significantly between different species. Scientists use the Greek root "tricho," meaning hair, to name these patterns. Monotrichous bacteria, such as Vibrio cholerae, possess only a single polar flagellum. Amphitrichous bacteria have one flagellum at each of two opposite ends. Lophotrichous bacteria have a tuft or crest of multiple flagella. These different arrangements allow different organisms to master their specific watery environments.