Centriolen

Centrioles are cylindrical organelles found in most animal cells and some lower plant forms. They are typically located within the centrosome, a region near the nucleus that serves as the main microtubule-organizing center. Centrioles play a crucial role in cell division, forming the spindle fibers that separate chromosomes. They are also involved in the formation of cilia and flagella, whip-like appendages that aid in cell motility or the movement of substances.

Structurally, a centriole consists of nine triplets of microtubules arranged in a pinwheel pattern. Each triplet is composed of three fused microtubules. Two centrioles are usually oriented perpendicular to each other within the centrosome, a structure known as the mother-centriole and the daughter-centriole. The mother-centriole, which is older, often bears appendages that help in the formation of basal bodies, the structures from which cilia and flagella grow.

Centrioles are replicated once during the cell cycle, ensuring that each daughter cell receives a centrosome. Their exact duplication mechanism is complex and involves precise regulation. While essential for cell division and the formation of motile appendages in many organisms, centrioles are absent in higher plants and fungi, suggesting alternative mechanisms for microtubule organization and cell division in these groups. The precise molecular machinery governing centriole assembly and function is an active area of research.