Cilia, Flagella, Centrosomes, & Centrioles

Learning Goals

By the end of this lesson, you will be able to:

• Describe the actions cilia and flagella perform within eukaryotic cells
• Explain the importance of cilia and flagella in carrying out their own functions and the
  functions of the cell
• Describe the structure and function of centrosomes within the cell
• Describe the structure and function of centrioles within the cell

Key Vocabulary

Cilia – tiny, hair-like structures that project from the surface of cells. They are found in many types of cells throughout the human body and have various functions, such as helping cells to move, creating fluid currents, or sensing the environment.

Flagella – whip-like structures that protrude from the surface of certain cells and are used for locomotion or movement.

Centriole – a cylindrical organelle found in eukaryotic cells that plays an important role in cell division.

Centrosome – an organelle found in eukaryotic cells that plays a key role in organizing the microtubules within the cell.

Cilia and Flagella

Cilia and flagella are microscopic hair-like structures that protrude from the surface of certain cells. They are composed of microtubules and play important roles in cellular movement, sensory perception, and fluid movement.

Flagella are typically longer and fewer in number than cilia and are used for locomotion. They can be found in various organisms, such as bacteria, algae, and sperm cells. For example, in bacteria, flagella rotate like propellers to move the cell through liquid environments, while in sperm cells, the flagellum propels the cell toward the egg.

Cilia, on the other hand, are shorter and more numerous than flagella. They can be found in many types of cells, including those in the respiratory tract, oviducts, and the brain. In the respiratory tract, cilia help move mucus and foreign particles out of the lungs, while in the oviducts, cilia help move the egg toward the uterus. In the brain, cilia play a role in sensing and transmitting signals.

Overall, the functions of cilia and flagella are critical for many biological processes, including cell movement, sensing things in the environment, and fluid transport. Without these structures, many organisms would not be able to survive and carry out essential functions.

Centrosomes

The centrosome is a crucial organelle that regulates the organization and growth of microtubules in a cell. Positioned near the nucleus, it serves as the microtubule organizing center. The centrosome is composed of two cylindrical centrioles, which have a unique pattern of microtubule arrangement. When a cell divides, the centrosome duplicates and moves to opposite poles of the cell, where it plays a crucial role in organizing the microtubules that make up the mitotic spindle.

Centrioles

Centrioles are small, cylindrical structures found in most eukaryotic cells. A pair of centrioles make up a centrosome. They play an important role in cell division and organization of microtubules in the cytoplasm.

During cell division, centrioles duplicate and move to opposite ends of the cell, where they help to organize microtubules into spindle fibers. These spindle fibers attach to the chromosomes and pull them apart during cell division, ensuring that each new cell receives the correct number of chromosomes.

Note: The video below labels the centrosomes even though Morgan says “centrioles.” Just remember that the centrioles are part of the centrosomes, which is why the video is labeled this way.

Centrioles also play a role in organizing microtubules in the cytoplasm, which is important for maintaining the cell’s shape and supporting the movement of cellular structures. The microtubules that originate from the centrioles can form cilia and flagella.

In addition to their structural role in cell division and organization of microtubules, centrioles have also been implicated in a range of cellular processes, including cell signaling and regulation of DNA repair.

While centrioles are not essential for cell survival, they are critical for proper cell division and function in many types of cells. Defects in centriole function have been associated with a variety of human diseases, including cancer and ciliopathies, which are characterized by defects in cilia and flagella formation and function.

Quiz