cytoskeleton structure

1. THE CYTOSKELETON
AND CELL MOVEMENT
Dr.Abhinav Golla MBBS, MD Pathology.
Asst Proff.
Medicure Diagnostics & reseaech center .
Vijayanagar colony. Hyderabad . Telangana

2. DEFINITION
• The ability of cells to adapt a
particular shape, maintain
polarity, organize the
relationship of intracellular
organelles, and move about
depends on the intracellular
scaffolding of proteins called the
cytoskeleton.

3. • Nevertheless, the cell membrane & intracellular organelles are not rigid or
static structures but are in a constant state of movement to accommodate
processes such as endocytosis, phagocytosis and secretion.
• Some cells (e.g. white blood cells) propel themselves about by amoeboid
movement; other cells have active motile membrane specialisations such as
cilia & flagella; while other cells (e.g. muscle cells) are highly specialised for
contractility.
• In addition, cell division is a process that involves extensive reorganisation of
cellular constituents.
• The cytoskeleton incorporates features
that accommodate all these dynamic function.

4. Structural elements of each cell

5. MICRO FILAMENTS
• Microfilaments are extremely fine
strands of protein actin
• Actin filaments are 5-9mm
diameter fibrils formed from the
globular protein actin (G-actin),the
most abundant cytosolic protein in
cells.
• The G-actin filaments monomers
noncovalently polymerize into long
filaments (F-actin) that intertwine
to form double-stranded helices
with defined polarity; new globular
subunits are added(or lost) at the
“positive” end of the strand.

6. • In muscle cells, the filamentous
protein myosin binds to actin and
moves along it, driven by ATP
hydrolysis( the basis for muscle
contraction)
• In non-muscle cells,F-actin
assembles via an assortment of
actin binding proteins into well-
organised bundles and networks
that control cell shape and
movement.

7. INTERMEDIATE FILAMENTS
• 10mm diameter fibrils that comprise a large and heterogenous family.
• Individual types have characteristic tissue-specific patterns of
expression that can be useful for assigning a cell of origin for poorly
differentiated tumors.*

8. Laminin A,B,C: nuclear lamina of all cells
Vimentin: mesenchymal cells(fibroblasts, endothelium)
Desmin: muscle cells, forming the scaffold on which actin & myosin
contract
Neurofilaments: axons of neurons, imparting strength & rigidity.
Glial fibrillary acidic protein: glial cells around neurons.
Cytokeratins: at least 30 distinct varieties, subdivided into
acidic(type1) and neutral/basic (type2); different types present in
different cells, hence can be used as cell markers.

9. IMMUNOHISTOCHEMICAL METHOD

10. MICROTUBULES
• Microtubules are 25nm thick fibrils composed of non-covalently
polymerized dimers of α- and 𝛽-tubulin arrayed in constantly
elongating or shrinking hollow tubes with a defined polarity; the ends
are designated “+” or “-” .
• The “-” end is typically embedded in a microtubule organising center
(MTOC or centrosome) near the nucleus where it is associated with
paired centrioles; the plus end elongates or recedes in response to
various stimuli by addition or subtraction of tubulin dimers.

11. • Within cells, microtubules can serve as connecting cables for “molecular
motors” proteins that use ATP to move vesicles, organelles, or other
molecules around cells along microtubules.
• There are two varieties of these motor proteins:
Kinesins, for anterograde(- to +) transport, and
Dyneins , for retrograde(+ to -) transport;
• They also participate in sister chromatid separation during mitosis.
• Notably, microtubules have been adapted to form motile cilia(e.g; in
bronchial epithelium) or flagella ( in sperm).

12. ABNORMALITIES OF CYTOSKELETON
• A number of blistering diseases of the skin are caused by
abnormalities of the cytoskeleton.
Epidermolysis bullosa simplex: mutations found in genes encoding for
cytokeratin 5&15

13. EPIDERMOLYSIS BULLOSA
MUSCULAR DYSTROPHY
PYLORIC ATRESIA

14. Take home message
property microtubules microfilaments Intermediate filaments
structure Hollow tubes;wall consists
of 13 columns of tubulin
molecules.
Two intertwined strands of
actin, each a polymer of
actin subunits,
Fibrous proteins
supercoiled into thicker
cables.
diameter 25nm with 15-nm lumen 7nm 8-12nm
Protein subunits Tubulin , a dimer
consisting of α-tubulin &
β-tubulin.
Actin One of several different
proteins of the keratin
family; depending on cell
type.
Main functions Maintenance of cell shape
(compression resisting
grinders)
Cell motility(as in cilia &
flagella)
Chromosome movement
in cell division
Organelle movements
Maintenance of cell shape
(tension bearing elements)
Change in cell shape
Muscle contraction
Cytoplasmic streaming
Cell motility(as in
pseudopodia)
Cell division(cleavage
furrow formation)
Maintenance of cell shape
(tension bearing elements)
Anchorage to nucleus and
certain other organelles
Formation of nuclear
lamina.