2. INTRODUCTION
• The cytoskeleton in cell biology is a system of fibrillar structures that diffuses the
cytoplasm.
• As such, it can be defined as the part of the cytoplasm which provides a cell with the
internal supporting framework.
• In addition to providing structural support, it is also involved in various types of
movement (where it supports specific cellular structures such as the flagellum) as well as
cellular matter movement.
• DEFINITION: The cytoskeleton is a network of filaments and tubules that stretches
throughout a cell, through the cytoplasm, which is all the substance within a cell except
the nucleus itself.
• It is found in all cells, although the proteins it is made of vary from organism to organism.
• The cytoskeleton supports the cell, shapes the organelles, organizes and teters them,
and plays a role in molecule transport, cell division and cell signaling.
3. • A cell's cytoskeleton ensures stability, energy, and motility.
• This provides a cellular scaffolding that arranges the cellular organization into.
• Note the cytoskeleton is extremely extensive.
• Notice that the cytoskeleton seems to have many ribosomes attached to it.
• Polysome refers to two ribosomes, or more.
• The ribosomes attached to the cytoskeleton are often referred to as' free' ribosomes to
differentiate them from those ribosomes attached to the membranes of the nuclear or
ER.
5. MICROFILAMENTS
• The thinnest are the microfilaments (7 nm in diameter) which are solid and are
principally made of two intertwined strands of a globular protein called actin. For this
reason, microfilaments are also known as actin filaments.
• Actin is powered by ATP to assemble its filamentous form, which serves as a track for
the movement of a motor protein called myosin.
• This enables actin to engage in cellular events requiring motion such as cell division in
animal cells and cytoplasmic streaming, which is the circular movement of the cell
cytoplasm in plant cells.
6. • Microfilaments are normally located at the periphery of the cell, where they run from
the plasma membrane to the microvilli (e.g. they can be discovered in the
pericanalicular zone where they form the pericanalicular web / meshwork).
• They are present here in bundles that together form an intracellular three -
dimensional meshwork.
•
• Microfilaments are highly diverse and versatile although they are the thinnest
components of the cytoskeleton.
7. FUNCTIONS
1.They maintain the shape of the cell.
2.Form contractile component of cells, mainly of the muscle cells.
3.White blood cells can move to the site of an infection and engulf the pathogen due to
microfilaments.
8. MICROTUBULES
• Microtubules are the largest of the three cytoskeleton components, with a diameter
ranging from 15 to 20 nm.
• Microtubules, unlike microfilaments, consist of a single type of globular protein known
as tubulin (a protein made up of kd polypeptides and alpha and beta tubulin).
• In favorable conditions, tubulin heterodimers join within the cell to form linear
protofilaments.
• Such filaments assemble in turn to form the microtubules (hollow tube-like straws).
• Like microfilaments, the cells often arrange microtubules into bundles.
• However, with some microtubules going through growth cycles and shortening of
their population, they have also been shown to be very unstable.
9. • Heterodimer subunits are separated from specific ends of the tubes during shrinkage
processes but inserted during the growth phase. This complex instability has been
attributed to the high variance in internal organization and size of the microtubule.
• Each microtubule consists of roughly 13 linear protofilaments arranged around a
hollow core.
• In a cell, microtubules emerge in a hub-spoke fashion from the center of the cell. They
radiate from here all through the cytoplasm where they perform a number of
functions.
10. • Unlike the other elements of the cytoskeletons, intermediate filaments comprise a
large family of polypeptides. For this reason, different types of cells contain a wide
variety of intermediate filaments.
• Studies have shown that there are more than 50 different types of intermediate
filaments classified into six major groups which include:
11. INTERMEDIATE FILAMENTS
• Unlike the other elements of the cytoskeletons, intermediate filaments comprise a
large family of polypeptides.
• For this reason, different types of cells contain a wide variety of intermediate filaments.
• Studies have shown that there are more than 50 different types of intermediate
filaments classified into six major groups which include:
12. • Type 1 and II – In most epithelial cells, it consists of about 15 different proteins.
• Type III - This group of proteins includes such as vimentin and desmin.
• Type IV - This group includes proteins such as α-internexin and neurofilament proteins
found in nerve cells.
• Type V - Lamins are an example of the proteins found in that group.
• Type VI - Found in neurons, just like nestin.
13. • Central rod domains of two polypeptide chains are first wrapped around each other
during assembly to form a coiled (dimer) structure. The resulting dimers then come
together to form tetramers which assemble to form protofilaments at their ends (end
to end). In the end, the protofilaments are assembled to form the intermediate
filaments.
• In terms of size, intermediate filaments range from 8 to 10 nm in diameter-So the word
"intermediate filaments." They are likewise more robust compared to the other two and
therefore more enduring.
14. MOTOR PROTEINS
• A number of motor proteins are found in the cytoskeleton.
• As their name suggests, these proteins actively move cytoskeleton fibers.
• As a result, molecules and organelles are transported around the cell.
• Motor proteins are powered by ATP, which is generated through cellular respiration.
There are three types of motor proteins involved in cell movement.
• Kinesins move along microtubules carrying cellular components along the way. They
are typically used to pull organelles toward the cell membrane.
• Dyneins are similar to kinesins and are used to pull cellular components inward
toward the nucleus. Dyneins also work to slide microtubules relative to one another as
observed in the movement of cilia and flagella.
• Myosins interact with actin in order to perform muscle contractions. They are also
involved in cytokinesis, endocytosis (endo-cyt-osis), and exocytosis (exo-cyt-osis).
15. CYTOPLASMIC STREAMING
• The cytoskeleton helps to make cytoplasmic streaming possible.
• Also known as cyclosis, this process involves the movement of the cytoplasm to
circulate nutrients, organelles, and other substances within a cell.
• Cyclosis also aids in endocytosis and exocytosis, or the transport of substance into and
out of a cell.
• As cytoskeletal microfilaments contract, they help to direct the flow of cytoplasmic
particles.
• When microfilaments attached to organelles contract, the organelles are pulled along
and the cytoplasm flows in the same direction.
• Cytoplasmic streaming occurs in both prokaryotic and eukaryotic cells.
• In protists, like amoebae, this process produces extensions of the cytoplasm known as
pseudopodia.
• These structures are used for capturing food and for locomotion.
16. CYTOSKELETON FUNCTION
• The cytoskeleton extends throughout the cell's cytoplasm and directs a number of
important functions.
• It helps the cell maintain its shape and gives support to the cell.
• A variety of cellular organelles are held in place by the cytoskeleton.
• It assists in the formation of vacuoles.
• The cytoskeleton is not a static structure but is able to disassemble and reassemble its
parts in order to enable internal and overall cell mobility.
17. CYTOSKELETON FUNCTION
• Types of intracellular movement supported by the cytoskeleton include transportation
of vesicles into and out of a cell, chromosome manipulation during mitosis and
meiosis, and organelle migration.
• The cytoskeleton makes cell migration possible as cell motility is needed for tissue
construction and repair, cytokinesis (the division of the cytoplasm) in the formation of
daughter cells, and in immune cell responses to germs.
• The cytoskeleton assists in the transportation of communication signals between cells.
• It forms cellular appendage-like protrusions, such as cilia and flagella, in some cells.
