Eukaryotic flagella – Its structure and function


Eukaryotic flagella are whip-like appendages found on the surface of some eukaryotic cells, such as algae and protozoa. They are used for movement and propulsion, as well as for sensory functions such as detecting chemicals or temperature changes.

Unlike bacterial flagella, which are made up of a single protein called flagellin, eukaryotic flagella are more complex structures that are composed of multiple different proteins. They are also longer and thicker than bacterial flagella, and they have a more complex internal structure.

Types of eukaryotic flagella 

There are two main types of flagella in eukaryotic cells: cilia and undulipodia. Some eukaryotic cells, such as sperm cells, have long flagella that look like whips. These are called undulipodia. They move by a process called an undulatory movement, in which the flagellum moves in a wavelike pattern. 

Cilia are shorter flagella that look like hair and are on the outside of many eukaryotic cells. They are used to move, sense the environment, and move substances across the surface of the cell, among other things.

Eukaryotic flagella are formed by a process called “flagellar synthesis,” which involves putting together proteins into the right shape. Genes and proteins work together in a complicated way to control this process.

Structure of eukaryotic flagella 

Eukaryotic flagella are more complicated than bacterial flagella, which are made of just one protein called flagellin. Eukaryotic flagella are made up of many different proteins, and their internal structure is more complicated.

Under the electron microscope, At the bottom of the flagellum is a structure called the basal body. It keeps the flagellum attached to the cell and gives it the power to move. The rootlet, the centriole, and the procentriole are the three main parts of the basal body. The procentriole is a small structure that looks like a rod and helps make new flagella. The centriole, on the other hand, is a cylinder-shaped structure that helps set up the cytoskeleton. The rootlet is a network of fibers that connects the base of the plant to the cell membrane.

The axoneme is the main part of the flagellum that holds it together. It is found above the base. It is made up of a set of microtubules that are arranged in a 9+2 pattern, with nine pairs of microtubules on the outside and two microtubules in the middle. Proteins called dyneins to move along the microtubules and create the force needed for movement. The central tubules have a set of radial spokes that connect them to the A tubules of the peripheral doublets. The doublets are linked together by a flexible protein link called the nexin link, which serves as an interdoublet bridge.  This keeps the microtubules in place. When the dyneins move, they make the microtubules slide against each other. This makes the flagellum bend and moves in waves.

A layer of the plasma membrane covers the surface of the flagellum. This membrane is full of proteins that help the cell sense things like chemicals or changes in temperature. There are also a number of signaling pathways in the plasma membrane. These pathways help control how the flagella move.

Structure of flagella
Cited from Karp’s cell and Molecular Biology: Concepts and Experiments.Wiley.

The function of eukaryotic flagella 

Movement and propulsion: As mentioned above, movement and propulsion are two of the most important jobs of eukaryotic flagella. Flagella are used to move the cell or organelle through the fluid around it. This can be done by undulating (as in undulipodia) or beating in waves (as in the case of cilia). This lets the cell or organelle figure out where it is in its environment and move toward or away from things like light or chemical gradients.

Sensory functions: In addition to helping eukaryotic cells move, flagella also help them sense their environment. The plasma membrane that covers the flagellum is full of proteins that can sense chemicals or changes in temperature in the environment. This lets the cell know what’s going on around it and act accordingly. For example, cilia in the olfactory system help detect smells, and cilia in the auditory system help detect sound waves.

Developmental function: The development of embryos also depends on the flagella of eukaryotic cells. In some cases, flagella help move gametes (like sperm) during fertilization. In other cases, they help move the developing embryo or larva.

Repair and maintenance functions: Flagella are also used to repair and keep tissues in good shape. For example, cilia in the respiratory system help move mucus and particles that have gotten stuck in the lungs out of the lungs. Cilia in the uterus help move the fertilized egg toward the uterus so that it can be implanted.

Immune functions: Pathogens can be removed from the body with the help of eukaryotic flagella, which are also involved in the immune response. For example, cilia in the respiratory system can help move bacteria and other pathogens out of the airways, and cilia in the urinary system can help move bacteria and other waste out of the body.

Overall, eukaryotic flagella play a vital role in a wide range of biological processes, including movement, sensory functions, development, repair and maintenance, and the immune response.

How eukaryotic flagella bends 

In an intact axoneme, the stem of each dynein molecule is tightly attached to the outside of the A tubule, and the globular heads and stalks point toward the B tubule of the next-door doublet.

  • In step 1, the dynein arms that are attached to the A tubule of the lower doublet attach to binding sites on the B tubule of the upper doublet. 
  • In step 2, the dynein molecules go through a conformational change, or power stroke, which makes the lower doublet slide toward the base of the upper doublet. This change in a dynein heavy chain’s shape. 
  • In step 3, the dynein arms have separated from the B tubule of the upper doublet. Step 4 is putting the arms back on the upper doublet so that the next cycle can start.
  • In Step 4 is putting the arms back on the upper doublet so that the next cycle can start. 


Iwasa, J., Marshall W.F., and Karp, G.(2020). Karp’s cell and Molecular Biology: Concepts and Experiments.Wiley.

Mubashir Iqbal
Mubashir Iqbal

Mubashir Iqbal is a highly dedicated and motivated Microbiologist with an MPhil in Microbiology from the University of Veterinary and Animal Sciences. Currently, he is researching the efficacy of commercially available SARS Cov-2 vaccines to neutralize the omicron variant in Pakistan. He holds a Bachelor's degree in Microbiology and has experience in chemical and microbiological analysis of water samples, managing SOPs and documents according to standard ISO 17025. Additionally, he has worked as an internee in BSL 3, Institute of Microbiology, UVAS, where he gained experience in RNA extraction, sample processing, and microscopy.

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