STPM Biology Structure of Cell and Organelle (Part 13)

Microtubules

Distribution:

• Found all over the cytoplasm of cells.
• For examples: cilia, flagella and centrioles.

Structure:

• Microtubules are tiny tubules composed of tubulin protein.
• The length of the microtubule varies. Its diameter is about 25nm; the diameter of the lumen is about 15nm.
• Microtubules can break and reassemble.

  

  Animal cell micrograph

Functions:

• Involved in cell division. Spindles are microtubules attached to chromosome during cell division.
• Microtubules in cytoplasm are vital in intracellular transportation. These microtubules contracts and relaxes continuously to move vesicles and organelles.
• Microtubules are cross-linked with microfilaments to form the cytoskeleton. This cytoskeleton provides mechanical support for the cell; it also determines the shape of the cell.
• Microtubules are main components of cilia and flagella. This shows that microtubule plays a part in movement of organisms or cells with cilia or flagella.
• Involved in formation of plant cell walls.

STPM Biology Structure of Cell and Organelle (Part 16)

Cilia and Flagella

Distribution:

Cilia:

• On protozoa (eg. Paramecium, Vorticella and Stentor)
• Respiratory tract (eg. trachea)
• Oviductus.

Flagella:

• On algae, a number of protozoa (eg. Euglena and Chlamydomonas) and a number of bacteria.
• Spermatozoa.

Structure:

• Cilium (plural: cilia) is a short, fine strand of hair, about 10μm long and 200nm in diameter.
• Flagellum (plural: flagella) is a long and fine strand of hair. Length: 10-150μm; Diameter: ~200nm.
• Cilia and flagella contain nine pairs of microtubules that are arranged in a ring around two central microtubules. Thus cilia and flagella are said to have a ‘9+2’ microtubule arrangement.
• Radial spokes connect the microtubule pair at the center to the peripheral microtubules.
• Each peripheral pair of microtubule has a pair of dinein arms.
• At the base of cilium and flagellum is the basal body. Basal body has a structure similar to the centriole. Basal body has a ‘9+0’ microtubule arrangement.
• On the outside of cilia and flagella is the plasma membrane.

Cilia and flagella structure

Functions:

• Cilia and flagella are for locomotion by protozoa.
• Cilia in the oviductus help to move ovum down the tube.
• Cilia on the lining of respiratory tracts trap particles.