CENTRIOLE, CYTOSKELETON AND VACUOLE

CENTRIOLES:

A minute cylindrical organelle near the nucleus in animal cells, occurring in pairs and involved in the development of spindle fibers in cell division.

Animal cells and cells of some microorganisms and lower plants contain two centrioles located near the exterior surface of the nucleus. In cross section each centriole consists of a cylindrical array of nine microtubules. However, each of the nine microtubules is further composed of three tubules. The two centrioles are usually placed at right angle to each other. Just before a cell divides, its centrioles duplicate and one pair migrates to the opposite sides of the nucleus. The spindle then forms between them. They are absent in higher plants. Centrioles play important role in the location of furrowing during cell division, and in the formation of cilia.

CYTOSKELETON:

A microscopic network of protein filaments and tubules in the cytoplasm of many living cells, giving them shape and coherence.

Cytosol contains cytoskeletal fabric formed of microtubules, microfilaments and intermediate filaments. The main proteins that are present in cytoskeleton are tubulin (in microtubules), actin, myosin, tropomyosin and others which are also found in muscles. Several cell organelles are derived from special assemblies of microtubules, for examples cilia, flagella, basal bodies and centrioles. The movement of cyclosis and amoeboid movements are because, of microfilaments, whereas intermediate filaments are involved in determination of cell shape and integration of cellular compartments.

Microtubules:

These are long, un-branched, slender tubulin protein structures. One very important function of mirotubules is their role in the assembly and disassembly of the spindle structure during mitosis.

Microfilaments:

These are considerably more slender cylinders made up of contractile actin protein, linked to the inner face of the plasma membrane. They are involved in internal cell motion.

Intermediate filaments:

They have diameter in between those of microtubules and microfilaments. They play role in the maintenance of cell shape. 

Vacuole:

A space or vesicle within the cytoplasm of a cell, enclosed by a membrane and typically containing fluid.

Although vacuoles are present both in animal and plant cells, they are particularly large and abundant in plant cells often occupying a major portion of the cell volume and forcing the remaining intracellular structures into a thin peripheral layer. These vacuoles are bounded by a single membrane and are formed by the coalescence of smaller vacuoles during the plant's growth and development. Vacuoles serve to expand the plant cell without diluting its cytoplasm and also function as sites for the storage of water and cell products or metabolic intermediates. The plant vacuole is the major contributor to the turgor that provides support for the individual plant cell and contributes to the rigidity of the leaves and younger parts of the plants.