Microvilli and Cilia Structure and Function

Microvilli Structure

• Microvilli are made up of five main proteins: actin, fimbrin, villin, myosin (Myo1A), and calmodulin.
• Actin filaments are cross-linked into closely packed bundles by actin bundling proteins, particularly fimbrin and villin.
• Actin filaments attach to the plasma membrane by lateral arms consisting of myosin I and calmodulin.

Cilia and Flagella

• Cilia and flagella are microtubule-based plasma membrane projections.
• Cilia act as antennae, sensing extracellular signals and facilitating movement.
• There are two types of eukaryotic cilia: primary (non-motile) cilia and motile cilia.
• Primary cilia are found on most animal cells and are involved in sensing extracellular signals, including movement, odorants, and light.
• Motile cilia are responsible for cell movement.

Motile Cilia

• Found on the surface of epithelial cells in the upper respiratory tract, uterine tubes (oviducts), and efferent ducts.
• Their functions include moving mucus over epithelial surfaces in respiratory epithelium (clearing dust particles, dead cells, and bacteria from respiratory passages) and transporting the ovum toward the uterus in the uterine tubes.

Cell Culture

• Living cells can be suspended in an appropriate liquid for examination under a light microscope, but they will soon die.
• Prolonged study of living cells can be achieved by cultivating them in solutions containing necessary nutrients to keep them alive.

Cell Culture Conditions

• Cell culture requires a medium that supplies essential nutrients (amino acids, carbohydrates, vitamins, minerals), growth factors, hormones, gases (O2, CO2), and a regulated physicochemical environment (pH, osmotic pressure, temperature).
• Most cells are anchorage-dependent and must be cultured while attached to a solid or semi-solid substrate.

Mammalian Cell Culture Medium

• Rich media are required and contain essential nutrients like amino acids (including 10 essential amino acids that cannot be synthesized by vertebrates and must be obtained from the diet), vitamins, various salts, glucose, and serum (containing factors needed for cell proliferation, including growth factors).
• Most animal cells can only grow on special solid surfaces like treated plastics and glass.
• The medium should be changed frequently.
• Aseptic technique is necessary to avoid contamination (antibiotics are employed).
• Cell culture is typically performed in laminar-flow hoods at a temperature of 37°C and pH 7.4 (phenol red is used as an indicator dye).

Primary Cell Culture vs Cell Lines

• Primary cell culture is derived from living tissue or organs, with cells isolated directly from human or animal tissue using enzymatic or mechanical methods. It has a limited lifespan.
• Cell lines are widely used for experiments and consist of eukaryotic cells that have acquired the ability to proliferate indefinitely through genetic mutations or artificial modifications. They are immortalized or continuous cell lines.

This quiz covers the structure and functions of microvilli, cilia, and flagella. Learn about the proteins involved in microvilli and how cilia serve as sensory and motile structures in eukaryotic cells. Test your understanding of these vital cellular components.