Centrioles are small, hollow cylinders found in animal cells, usually in a pair lying at right angles to each other near the nucleus. Each centriole is about 0.2 µm wide and 0.4 µm long and has no membrane.
Structure
Each centriole is made of microtubules, hollow tubes of the protein tubulin. The microtubules are arranged in nine triplets (groups of three) around the edge of the cylinder, the so-called 9 × 3 arrangement. The pair of centrioles, together with the surrounding material, forms the centrosome, the main microtubule-organising centre of an animal cell.Functions
• Cell division: before a cell divides, the centrioles replicate. During mitosis and meiosis, one pair moves to each pole of the cell, and the centrosomes organise the spindle fibres (microtubules) that attach to the chromosomes and separate them.
• Cilia and flagella: centrioles move to the cell surface and act as basal bodies, from which the microtubules of cilia and undulipodia (eukaryotic flagella, as in the sperm tail) grow.Distribution
Centrioles are present in animal cells and many protoctists and some fungi, but are absent from the cells of most flowering plants and conifers. These plant cells still form a spindle, organised by other microtubule-organising regions, which shows that centrioles are not essential for spindle formation.
StructureEach centriole is made of microtubules, hollow tubes of the protein tubulin. The microtubules are arranged in nine triplets (groups of three) around the edge of the cylinder, the so-called 9 × 3 arrangement. The pair of centrioles, together with the surrounding material, forms the centrosome, the main microtubule-organising centre of an animal cell.Functions
• Cell division: before a cell divides, the centrioles replicate. During mitosis and meiosis, one pair moves to each pole of the cell, and the centrosomes organise the spindle fibres (microtubules) that attach to the chromosomes and separate them.
• Cilia and flagella: centrioles move to the cell surface and act as basal bodies, from which the microtubules of cilia and undulipodia (eukaryotic flagella, as in the sperm tail) grow.Distribution
Centrioles are present in animal cells and many protoctists and some fungi, but are absent from the cells of most flowering plants and conifers. These plant cells still form a spindle, organised by other microtubule-organising regions, which shows that centrioles are not essential for spindle formation.