TOPIC 19. Nonmembranous cell organelles – Cytocenter
Centrioles
Centrioles are discs built from microtubule material, with nine microtubule triplets arranged in a cylinder. Each of the nine triplets has two connecting microtubules. When the cell is not dividing, two centrioles are paired with each other at 90 degree angles. Along with some other proteins, the two centrioles combine to make the centrosome.
Centriole – composed of nine microtubular triplets (9x3)
Centrosome
The centrosome is an organelle and it is the microtubule-organizing centre MTOC for the mitotic spindle and consists of paired centrioles and proteins. The proteins are responsible for the anchoring of the microtubules. The spindle fibres develop from the centrosome during cell division.
Two centrioles in a centrosome exist at right angles to each other
Functions of centriole:
- 1. Formation of mitotic spindle
- 2. Generation of cell’s cytoskeleton – formation of cilia and flagella and building of their basal bodies
- 3. Before cell division/interphase each centrosome duplicates itself so that now each centrosome has two pairs of centrioles. During mitosis, the centrosome divide into halves, which move to opposite poles of the cell and become organising centres for the microtubules of the mitotic spindle
Role of centrosome:
Centrosomes are associated with the nuclear membrane during prophase of the cell cycle.
In mitosis the nuclear membrane breaks down and the centrosome nucleated microtubules (parts of the cytoskeleton) can interact with the chromosomes to build the mitotic spindle. The mother centriole, the one that was inherited from the mother cell, also has a central role in making cilia and flagella.
The centrosome is copied only once per cell cycle so that each daughter cells inherits one centrosome, containing two structures called centrioles. Centrosomes are required for survival of the organism.