Overview
This lecture explains the structure and functions of cilia and flagella, highlighting their similarities, differences, and their roles in cell movement and substance transport.
Structure and Function of Cilia and Flagella
- Cilia and flagella are cytoplasmic projections aiding movement in various cells.
- Flagella are long, whip-like structures, usually single or few, for locomotion in bacteria, sperm, and some plant/animal cells.
- Cilia are short, hair-like projections, numerous on the cell surface, moving substances over cell surfaces (e.g., in the respiratory tract, fallopian tubes).
- Both structures are anchored by the basal body (blepharoplast), which is similar to a centriole (9 triplet microtubule arrangement, called 9+0).
- Rootlets anchor the basal body in the cytoplasm, providing support.
- Above the basal body is the basal plate, where microtubule arrangement changes from triplets to doublets.
- The shaft consists of nine peripheral doublets and two central singlets of tubulin (9+2 arrangement).
Detailed Microtubule Arrangement
- Tubulin proteins (A and B types) form pairs (doublets) in the flagella and cilia shaft.
- The 9+2 arrangement: 9 doublets form a circle around 2 central singlets.
- Dynein protein "arms" with ATPase activity connect adjacent doublets, enabling movement.
- Radial spokes connect the central pair to peripheral doublets for stability.
- Nexin protein links adjacent doublets, maintaining structural integrity.
- The shaft is usually surrounded by a cell membrane, except sometimes in sperm tails.
Differences Between Cilia and Flagella
- Cilia are shorter, numerous, and cover the cell surface; flagella are longer and fewer.
- Cilia move with a pendular (one-directional) motion; flagella undulate in a rotary manner.
- Cilia function in movement, feeding, and aeration; flagella mainly provide movement.
Key Terms & Definitions
- Cilia — Short, hair-like projections on cell surfaces that move substances.
- Flagella — Long, whip-like projections aiding in cell movement.
- Basal body/Blepharoplast — Structure anchoring cilia/flagella, similar to centrioles.
- Microtubules — Tubular proteins (A and B tubulin) forming the structural core.
- 9+2 arrangement — Nine doublets surround two central microtubules in cilia/flagella shafts.
- Dynein — Motor protein facilitating movement using ATP.
- Nexin — Protein linking adjacent microtubule doublets.
- Rootlets — Fibrous structures anchoring the basal body in the cytoplasm.
Action Items / Next Steps
- Research and find out what stimulates sperm flagella movement and its energy source.
- Optional: Review centriole structure and function for deeper understanding.