2. What is cytoskeleton?
• The cytoskeleton is a network of different protein fibers that provides many functions:
• it maintains or changes the shape of the cell; it secures some organelles in specific
positions; it enables movement of cytoplasm and vesicles within the cell; and it enables
the cell to move in response to stimuli.
• Centrosomes, centrioles, and the locomotory structures like-cilia and flagella are made up
of cytoskeletal elements.
4. • Centrioles are found in animal cells, in some lower plant cells, and at the base of flagella and cilia, they are
absent in higher plants.
• it was first discovered by Boveri and Van Beneden in the 1880s, the centriole remains a surprisingly
mysterious organelle.
• Centrioles play a role in organizing microtubules that serve as the cell's skeletal system.
• They help determine the locations of the nucleus and other organelles within the cell.
5. Structure:
• In cell biology a centriole is a cylindrical organelle composed mainly of a protein
called tubulin .
• Centrioles are found in most eukaryotic cells, but are not present in conifers
(Pinophyta), flowering plants (angiosperms) and most fungi, and are only present
in the male gametes of charophytes, bryophytes, seedless vascular plants, cycads,
and Ginkgo.
• A bound pair of centrioles, surrounded by a highly ordered mass of dense
material, called the pericentriolar material (PCM),makes up a structure called
a centrosome.
• All the centrioles are formed of 9 groups of microtubule triplets organized in a
cylindrical shape.
• The detailed structure of centrioles can be studied only under an electron
microscope.
• These are associated together at right angles to each other.
• The embryo of Drosophila melanogaster and C. elegans are exceptions to this
organization.
• The former forms 9 pairs instead of microtubule triplets, whereas the premature
embryos and sperm cell of C. elegans have 9 single microtubules.
6. • Function of a Centriole :
• Cells form a complex endoskeleton of microtubules which allows substances to be transported to
any location in a cell
• Products are tagged with special glycoproteins (sugar and protein) which act as signals to specific
motor proteins.
• These proteins attach to the product, or vesicle that the product is stored in, and also attach to a
microtubule.
• Microtubules are arranged at the centriole, of which each centrosome has two. The centrioles
anchor the microtubules that extend from it and contain the factors needed to create more tubules.
• During mitosis, centrosomes are replicated by duplicating each centriole.
• The 4 centrioles then divide into two centrosomes, each with one centriole at a right angle to the
second centriole.
• Microtubules extend between the centrosomes which push the sets of centrioles apart. The
centrioles will be pushed apart, to opposite ends of the cell.
• Once established, each centriole will then extend microtubules into the cytoplasm that seek out
chromosomes.
• The microtubules attach to the chromosomes at their centromeres, which are parts of the DNA
specially formulated to allow the attachment of special proteins and microtubules.
• The microtubules are then disassembled from the centriole, which draws the microtubule back
toward the centriole, as motor proteins pull the chromosomes apart.
7. • Centriole helps in organizing the mitotic spindle and complete the process of cytokinesis.
• However, centrioles were believed to be necessary for the formation of the mitotic spindle
in the animal cell.
• Although, several recent types of research have explained that the cell which does not
have a centriole (surgically removed through laser) can function without it in the G1 level
of interphase and can be formed later in a de novo manner.
• The location of the centrioles plays a key role in the three-dimensional organization of the
cell as it also regulates the location of the nucleus.
• In flagellated and ciliated organisms the location of such organelle is decided after the
mother centrioles that form the base.
