# INTRODUCTION:-

-> Centrioles are cytoplasmic organelles.

-> Mostly found in eukaryotic cells and are present in pairs called centrosomes.

-> Centriole lack a limiting membrane and DNA or RNA. 

-> Forms the spindle of microtubules during cell division (mitosis and meiosis).

-> Each centriole lies at a right angle to the other.

-> Surrounded by amorphous pericentriolar material.

# STRUCTURE:-

-> The length of the centriole is about 3,000 to 5,000 Ã and the diameter is about 1,500 to 1,800 Ã.

-> Centrioles are made up of lipids and protein and also contain carbohydrates.

->  Centrioles are a set of microtubules. Arranged in the form of open-ended cylinders.

-> Made up mainly of tubulin protein (alpha tubulin and beta tubulin).

-> Centrioles mainly consist of 9 evenly spaced peripheral triplet fibrils of microtubules.

-> The nine triplet microtubules are arranged in a pattern of 9+3,  linked with the help of an A-C linker.

# DUPLICATION:-

-> Before chromosome replication, the cell contains two centrioles(centrosome).

-> In the centrosome, the older centriole is termed the mother centriole and the other one is termed the daughter centriole.

-> During S-phase of the cell cycle, new centrioles grow at the proximal end of the mother and daughter centrioles.

-> The two pairs of centrioles remain attached to each other until mitosis.

-> They separate in mitosis with the help of the enzyme ‘separase’.

#FUNCTIONS:-

1) Cellular organisation;

-> Centrioles are involved in organising microtubules in the cytoplasm.

-> The position of the centriole in the cell determines the position of the nucleus and plays a critical role in the arrangement of cell organelles.

2) Formation of cilia and flagella:-

-> Centrioles form basal bodies, which give rise to axonemes of cilia and flagella. 

3)  In Cell division:-

∆ Mitosis.

• Mitosis is divided into four stages:-

1. Prophase

-> Prophase is marked by condensation of chromosomal material.

-> The nuclear membrane starts dissolving.

-> The centrioles(which are divided during S-phase) move to opposite ends of the nucleus.

-> The mitotic spindle fibres appear. 

2. Metaphase

-> In metaphase, spindle fiber attached with the centromere at the kinetochore (a protein structure where the spindle fiber attached).

-> Centrioles are at opposite poles; centrioles pull the chromosomes to the centre of the cell (metaphase plate).

3. Anaphase

-> During anaphase, chromosomes split lengthwise, and sister chromatids separate.

-> The spindle fibres contract, and they pull one sister chromatid towards the opposite pole.

Tw4. Telophase

-> The cell division occurs in telophase.

-> The nuclear membrane reappears around the chromatid cluster.

-> The new daughter cells contain a pair of centrioles. 

“From organising microtubules to helping cells divide, centrioles prove that even the smallest structures matter.”