# INTRODUCTION:-

-> Centrioles is a cytoplasmic organelles.

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

-> Centriole lack limiting membrane and DNA or RNA. 

-> Form spindle of microtubule during cell division (mitosis and meiosis)..

-> Each centrioles lie at right angle to each other.

-> Surrounded by amorphous pericentriolar materials.

# STRUCTURE:-

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

-> Centrioles is made up of lipid and protein, also contain carbohydrates.

->  Centriole is a set of microtubules. , arranged in form of open ended cylinders.

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

-> Centrioles mainly consists 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 a-c linker.

# DUPLICATION:-

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

-> In the centrosome the older centriole is termed as mother centriole and another one is termed as daughter centriole.

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

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

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

#FUNCTIONS:-

1) Cellular organization ;

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

-> The position of centriole in cell determine the position of nucleus and play 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 start dissolving.

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

-> The mitotic spindle of threads appear. 

2. Metaphase

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

-> Centrioles are at the opposite poles of each other, centrioles pull the chromosome to the center of cell (metaphase plate).

3. Anaphase

-> During anaphase chromosome splits lengthwise, sister chromatids separate.

-> The spindle fiber centrioles contract and they pull one sister chromatid towards opposite pole.

Tw4. Telophase

-> The cell division occur in telophase.

-> Nuclear membrane reappear around the chromatid cluster.

-> The new daughter cells contains pair of centrioles. 

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