Cytoskeleton Function in Animal Cell
1.3.7 Cytoskeleton
The cytoskeleton (Gk: Kytos, cell; Skeleton, dried body) are unbranched cylindrical structure that is made up of proteins and involved in internal structure, movement, contraction, relaxation, and maintain cell shape.
There are three types of cytoskeleton elements based on size and chemical composition, i.e., microtubules, microfilaments, and intermediate filaments.
Microtubules:
These are small hollow cylinders, made of self-assembling tubulin protein, 25nm in diameter. In plants, microtubules are often found associated with the cell walls. Perhaps these are involved in the transport of cell wall materials from Golgi bodies to the outside of the cell.
During cell division, these microtubules form spindle fibers. Several cell organelles are also derived from a special assemblage of microtubules e.g., cilia, flagella, basal bodies, and centrioles.
Microfilaments:
Microfilaments are considerably more slender, made up of a contractile protein called actin, and linked to the inner face of the plasma membrane. These are about 7.0 nm in diameter and occur in bundles or mesh-like networks. Actin filament contains two chains of actin molecules twisted to each other. Besides the actin protein tropomyosin and troponin proteins are also present.
These perform functions of muscle contraction and change in cell shape including division of cytoplasm during cell division.
Intermediate filament:
These filaments are called intermediate because they are intermediate in size between microfilament and microtubule (about 8-12nm) in diameter. These are composed of vimentin protein. The intermediate filaments assemble and disassemble and, therefore, play an important role in maintaining the shape of the cell, attachment of muscle cells, and support of nerve cell processes i.e. axon.
1.3.8 Peroxisomes
It is a tiny single membrane-bound cell organelle, which contains a large amount of oxidative enzymes (such as peroxidase, catalase, de-amino acid oxidase, etc.). These are spherical-shaped organelles about 0.6 to 0.7μm in diameter. Their number varies between 70 to 100 per cell. It was first isolated by De Duve and co-workers in 1965 in liver cells and other tissues that are rich in oxidative enzymes. It is also found in protozoans, yeasts, and many higher plants.
Function
The name peroxisome was applied because this organelle is specifically involved in the formation and decomposition of hydrogen peroxide (H, O,) in the
cell.
1.3.9 Glyoxisomes
These are cell organelles, mostly found in lipid-rich seeds and seedling cells of plants. These contain enzymes like glycolic acid oxidase and catalase. Some other enzymes are also present that are involved in the conversion of I carbohydrate by a process called the glyoxylate cycle.
Centrioles are non-membranous organelles, two in numbe 08158Pids into
1.3.10 Centrioles
located near the outer surface of the nucleus. The diameter of the centriole is 10nm. They are found in animal cells of some microorganisms and lower plants while absent in higher plants. Centrioles were discovered by Beneden in 1883
Structure:
The cytoplasm surrounded Centrid Boveri in 1895. is called "centrosphere". Centrioles and centrospheres are collectively called centrosomes. In cross-section, each centriole consists of a cylindrical array of nine microtubules. However, each of the nine microtubules is further composed of triplet tubules. Both centrioles are placed at a right angle to each other.
Function
They help in cell division. They are self-replicating units and replicate just before the cell division. Each pair migrates towards the opposite side of the nucleus. The spindle fibers are formed between
these two pairs of centrioles. They play an important role in the location of furrowing during cell division and the arrangement of microtubules.
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