This presentation offers a brief idea about the exoskeleton and it's different types along with the basic idea of cytodifferentiation. Micro-tubules, Micro-filaments and Intermediate filaments, their structure along with their functions have been widely explored along with the diagrams taken from Google images. The presentation also offers the biophysical and biochemical principles to address the issues of cytoskeleton for the cellular integrity and dynamism. The different types of diseases in humans due to cytoskeleton damages and defects have been widely explored. The cytodifferentiation has been explained to make the subject more informative in this regard.

1. CYTOSKELETON: ROLE AND STRUCTURE OF MICROTUBULES,
MICROFILAMENTS AND INTERMEDIARY FILAMENT &
CYTODIFFERENTIATION
Dr. Nandadulal Sannigrahi,
Associate Professor,
Department of Botany,
Nistarini college, Purulia
D.B. Road, Purulia,
INDIA (W.B)

2. CYTOSKELETON
 The Cell have to number of functions for the sake structural integrity and
the functional mobility within the cell,
 The special network developed within the cell play a significant role in this
regard is cytoskeleton.
 The cytoskeleton of animal cells is one of the most complicated and
functionally versatile structures, involved in processes such as Endocytosis,
cell division, intra-cellular transport, motility, force transmission, reaction to
external forces, adhesion and preservation, and adaptation of cell shape.
These functions are mediated by three classical cytoskeleton filament types,
as follows: Actin, microtubules, and intermediate filaments.
 The named filaments form a network that is highly structured and dynamic,
responding to external and internal cues with a quick reorganization that is
orchestrated on the time scale of minutes and has to be tightly regulated.
 These cytoskeleton proteins differ not only in their chemical structure, but
also in the type of filaments and structures they form, ranging from fast
assembling.

3. CYTOSKELETON

4. CYTOSKELETON- TYPES
 Cytoskeleton are of three types- Microtubules, Microfilaments and
Intermediate filaments,
 Microtubules- A network of microtubules , 25-30 nm in diameter just below
the plasma membrane,
 Microfilaments- Cytoplasmic network of actin filaments called
microfilaments , 5-7 nm in diameter,
 Intermediate filaments- With a diameter of 10 nm, these filaments play an
important role in maintaining the structure and function of cell.
 Each of the cytoskeletal components is composed of simple protein subunits
that polymerize to form filaments of uniform thickness,
 These filaments are not permanent structure ; they undergo constant
disammebly into their monomeric sub units and reassembly of filaments,
 The location of the filaments are not fixed but they may change dramatically
with mitosis, cytokinesis or changes in the cell shape.

5. MICROTUBULES
 First observed by De Robertis and Franchi (1953) in the axoplasm of
myelinated nerve fibers,
 Exact nature of microtubules brought about by Sabatini, Bensch and
Berenett (1963),
 Microtubules of plant cells was explored by Ledbetter and Porter (1963),
 Both in plant and animal cells, microtubules are found to occur in Cilia or
flagella, Centrioles and basal bodies, Nerve processes, Mitotic apparatus,
the cortex of meristematic plant cells, elongating cells during
spermatogenesis and some selected structures of protozoa,
 STRUCTURE
 Long, hollow cylinders, outer diameter is 250 A, with hollow core and the
thickness of wall,
 Cytoplasmic microtubules shows 13 subunits – protofilaments , parallel to
the long axis of the microtubules, number may vary like 15 in cockroach
epidermis and 12 in crayfish nerve,

6. MICROTUBULES

7. MICROTUBULES
 The proto-filaments are made up of a linear series of globular proteins-
tubulin in the form of the strings of beads,
 Under physiological conditions, tubulin is a dimer composed of two similar
units – α tubulin and β- tubulin with Mol w. 55000 and 57000 respectively,
 The amino acid composition of the proteins subunits are like muscle protein,
actin or microfilament,
 Tubulin being helical nature, consists of 13 tubulin molecules per turn.
Beside tubulin, 20-25 secondary proteins called Microtubules associated
Proteins ( MAP) are important to make the connection,
 Kinesin and cytoplasmic dynein proteins bind to microtubules and move
along them using ATP to drive its motion,
 Each tubulin has two nucleotide binding site and is bound to GTP . One
molecules bind strongly while other binds loosely. Brain tubulin contains at
least one mol of Mg ++ per mole of tubulin dimer.
 Assembly of microtubules is complex series of steps needs the biochemical
issues,

8. MICROTUBULES- FUNCTION
 Microtubules perform a number of functions-
 Mechanical Function-The shape of cells and protuberance like cilia,
flagella, dendrites are correlated to orientation and distribution of
microtubules,
 Cell membrane movement- Microtubules acts as cell muscle and involved in
cell membrane movement during pseudopodia activity, Endocytosis ,
extension of microvillus etc.
 Movement of Cilia and Flagella- The axial supports of cilia and flagella are
made up with microtubules which are associated with the movement of cilia
and flagella with the cost of ATP,
 Chromosomal movement during cell division- Specific shortening of
microtubules in involved with the kinetochores and thus splitter
chromosome movement towards opposite poles during the late metaphase,
 Circulation and transport- Transport of micro molecules in the cell interior
like melanin pigment movement through the channels of microtubules,
 Morphogenesis- Shaping of cell during cyto-differentiation particularly
spermatogenesis or muscle cell orientation in the embryo.

9. MICROFILAMENTS

10. MICROFILAMENTS
 Microfilaments, also called actin filaments, are the thinnest components of
the cytoskeleton, about 7 nm in diameter, and are composed of two
intertwined strands of the protein actin.
 Microtrabecular lattice is found in the three dimensional view of
microfilaments,
 The channels provide rapid diffusion of fluids and metabolites throughout
the cytosol,
 The filaments of lattice are in contact with the ER, microtubules and
polysome but mitochondria remain free in the lattice,
 When the lattice undergoes contraction, there is a bending of
microtrabecullae,
 They are dynamic and can be quickly assembled and disassembled, which
allows for cell shape changes, cell movement, and intracellular transport.
Key functions include muscle contraction (via interaction with myosin), cell
division, and creating structures like microvillus,

11. MICROFILAMENTS
 Microfilaments contain a number of proteins like actin, myosin,
tropomyosin,α- actnin etc,
 ACTIN
 It constitutes 20% of those proteins present in globular form and may
polymerize to form the microfilaments of fibrous actin,
 The cytoplasmic actin is similar to muscle actin consisting double helical
array of G-actin molecules,
 Actin-myosin complex has an arrow like shape with definite polarity ,
monomers can be added both the ends,
 Actin filament can be fragmented spontaneously to produce new nucleation
centre on a few monomers of G-actin aggregate to start nucleation.
 MYOSIN
 Myosin with molecular weight of 500000 at very low concentration ,
 All myosin filaments bind reversibly to actin filaments and contain Ca++
and activated ATP-ase,

12. MICROFILAMENTS
 Myosin filaments are 13-22 nm. In thickness,
 ACTIN-BINDING PROTEINS
 Cytoplasmic gel of macrophage has actin binding proteins which can be
grouped into three functional cases-
 Those promote cross-linking during geletion,
 Those able to serve the long actin filaments by capping to short fragments
during solation,
 Those proteins that tend to stabilize actin in G-form . Causing solation.
 Actin cross linking proteins establish the cross-links between actin
microfilaments resulting in are dimensional network,
 The protein filamin , holds two filaments together where they cross at right
angles.
 The protein, foldrin is another protein by which the filaments are cross-
linked and form side-by-side aggregates or bundles,
 Spectrin , a cross linking protein found in the cytoskeleton of RBC ,
 Villin is another cross-linking protein found in intestinal microvilli

13. INTERMEDIATE FILAMENTS
 Intermediate filaments are rope-like structural proteins that form a network
within the cell, providing mechanical strength and helping the cell maintain
its shape.
 They are composed of different types of fibrous proteins, are about 10 nm in
diameter (between microfilaments and microtubules), and play a critical role
in resisting tension, anchoring organelles, and forming cell-to-cell junctions,
 These filaments are intermediate in thickness (10 nm) between microtubules
and microfilaments,
 Having similar structural organization between intermediate filaments
despite heterogeneity,
 Formed by protein subunits of multigene class that are expressed
differentially in various cell types ,
 Different intermediate filaments proteins are organized in a similar way
forming tetrameric complexes,

14. INTERMEDIATE FILAMENTS

15. INTERMEDIATE FILAMENTS & TYPES
 Each basic unit of an intermediate consists of a dimmer composed of two α-
helical chains,
 These chains are oriented in parallel or intertwined protein filaments in a coiled
coil rod,
 The highly conserved head and tails are oriented in a definite head to tail
fashion,
 Four dimmers are associated in an antiparallel half staggered manner to produce
4-5 nm diameter protofibrils , and three to fur such protofibrils intertwine to
produce an apolar intermediate filaments.
 DIFFERENT TYPES OF INTERMEDIATE FILAMENTS
 There are four main types of intermediate filaments-
 Keratin filaments- Also known as tonofilaments, prekeratin or cytokeratin,
 Filaments are anchored to cell surface and tend to converge upon the
desmosome,
 In the epithelial cells, it forms keratin from the dead layers of stratum corneum,
 The size is ranging from 47000-58000 Daltons.

16. INTERMEDIATE FILAMENTS & TYPES
 Neurofilaments –
 Together with microtubules. It forms axon, dendrites and neuronal
perikarya,
 These are very sensitive to proteolysis in presence of Ca++,
 They form three dimensional lattice that converts axoplasm in a highly
structured gel,
 It is of three types- NF-1, NF-M and NF-H.
 Glial Filaments- Found throughout the cytoplasm of astrocytes and are
composed of a very acidic protein of mol. Wt. 51000 Daltons,
 Heterogeneous filaments- Intermediate filaments have similar morphology
and localization but different proteins such as desmin, vimentin and
synemin.
 In skeletal muscle, the myofibrils are held by a linkage present at the Z- and
M- lines,
 Three proteins have wide distribution and network.

17. INTERMEDIATE FILAMENTS-FUNCTIONS
 The intermediate filaments perform multiple roles for cellular integrity and
mechanical outcomes for the cell sustainability and dynamism to perform
the diverse functions in a coordinated manner. The error here may cause
irreparable damages as stated below:
 Mechanical support
 Tension bearing: Intermediate filaments are strong and flexible and bear
mechanical tension, which prevents cells from being stretched and distorted.
 Tissue integrity: They anchor cells to each other and to the extracellular
matrix, providing structural support that strengthens tissues against
mechanical stress.
 Cellular strength: They provide resistance against shear stress, making
them particularly abundant in tissues that undergo a lot of mechanical stress,
such as skin.
 Cellular organization
 Organelle anchoring: They anchor the nucleus and other organelles,
positioning them within the cytoplasm and preventing them from moving
too freely.
 Nuclear lamina: A network of intermediate filaments in the nucleus, called
the nuclear lamina, helps maintain the nucleus's shape and stability.
 Cytoplasmic organization: They act as an organizer of cytoplasmic space,
influencing the positioning of various cellular components and organelles.

18. INTERMEDIATE FILAMENTS-FUNCTIONS
 Cell-cell junctions: They are involved in forming specialized junctions
between cells.
 Signal transduction: They play a role in cell signaling and growth
regulation.
 Intracellular transport: They are involved in organizing and facilitating
intracellular trafficking.
 During mitosis, the intermediate filaments undergo reversible disintegration
and restoration,
 They may interact with microtubules and help in the motility process
making a bridge between microtubules and intermediate filaments,
 Mutations in the genetic sequences for intermediate filaments can cause
diseases like epidermolytic hyperkeratosis, epidemolytic palmoplanar
peratoderma, amystrophic lateral sclerosis , cardiovascular lesions and
skeletal muscle myopathy like misfortunes causing distress to the patients
and even the death.

19. CYTODIFFERENTIATION
 Cytology deals with cell & differentiation is the further modification of the
newly borne cells to undergo specialization to perform desired function with
shape.
 So, during the growth and the maturation of the callus tissue or free cells in
suspension culture, few dedifferentiated cells undergo cytoquiesence and
cytosenesence and these twin phenomenon are mainly associated with the
differentiation of vascular tissues in general and tracheary elements & sieve
tubes in particular. Not only in plants, the animal kingdom also envisages
this complex biological orchestra for the complete development of the entire
body along with regeneration of body parts in need in almost all the
consequences.
 This whole developmental process is called Cytodifferenciation.
 Thus , Cytodifferentiation is defined as the development of specialized cells
from unspecialized ones through the stimulation of specific nutritional and
hormonal factors. In tissue culture, the differentiation of callus or single
cells in suspension culture is the result of dedifferentiation of a few cells due
to the twin phenomenon of cytoquiscence and cyto-senescence.

20. THANK YOU FOR YOUR VISIT
 ACKNOWLEDGEMENTS:
a. Google for images,
b. Different websites for enriching the course content,
c. Science Direct pages,
d. A textbook of Botany- Vol III – Hait, Bhattacharya & Ghosh.
e. A Text Book of Cell and Molecular Biology- Ajay Paul,
f. Cell and Molecular Biology- Kar and Halder,
g. Concept of Genetics- Klug. Cummings, Spencer, Palladino,
DISCLAIMER:
This presentation has been designed to address the academic fraternity
without any financial interest. This is absolutely free to use . The author
does not claim any kind of financial benefits from this content.