The document discusses the structural framework and functions of the cytoskeleton in eukaryotic cells, highlighting its role in transporting materials and maintaining cell shape. It defines the three main components of the cytoskeleton—microtubules, microfilaments, and intermediate filaments—and their specific functions in cellular movement, structural integrity, and cell division. Additionally, it emphasizes the dynamic nature of these structures, which adapt to changes within the cell.

1. Structural framework of a
cell
G.Keertana
Tutor
Department of biochemistry

2. Time to think….
1. How can the cell purposely move and control the location of
materials between these organelles?
2. How can a eukaryotic cell transport compounds
from their place of origin (in most cases the cyotoplasm) to
where they are needed (perhaps the nucleus, the
mitochondria, or the cell surface)?

3. ● One possible solution is for the cell to
create a network that can connect all
the different parts of the cell together
● we can use a map to determine the
direction we need to travel and roads
to connect and travel from home to
campus.
● Likewise, an interconnecting network
inside the cell can be used to direct
and move compounds from one
location to a final destination

5. Intracellular network
● Needs to be extensive, and connect every area of the cell.
● Needs to be flexible, able to change and adapt as the cell
grows larger, divides into two cells, or physically moves
from one environment to another.
● Needs to be strong, able to hold up to mechanical
pressure from inside the cell or from outside of the cell.

6. Intracellular network
● Needs to be composed of different fibers and each of these fibers needs
to be for a specific connection in the cell. For example, certain fibers
might be involved in holding organelles in place, and other fibers would
be involved in connecting two different organelles.
● The fibers need to have directionality (or polarity), meaning they need
to have a defined starting point and a defined end to help direct
movement from one location to another.
● The fibers need to work with proteins that can convert chemical energy
into kinetic energy, to actively transport compounds along the fibers.

7. The skeleton of a vertebrate
is a familiar organ system consisting of hardened elements that support the
soft tissues of the body and play a key role in mediating bodily movements.

8. Eukaryotic
cells also
possess a
“skeletal
system” –
a
cytoskelet
on –which
has
analogous
functions.
The answer
is
Cyto skeleton…

9. Functions of Cyto-Skeleton
● Providing structural support that can determine the shape
of the cell and resist forces that tend to deform it.
● An internal framework responsible for positioning the
various organelles within the interior of the cell.
● A network of highways that direct the movement of
materials and organelles with cells
Eg: delivery of mRNA molecules to specific parts of a cell,
the movement of membranous carriers from the
endoplasmic reticulum to the Golgi complex, and the
transport of vesicles containing neurotransmitters down
the length of a nerve cell.

10. Functions of Cyto-Skeleton
● The force generating apparatus that moves cells from
one place to another.
● A site for anchoring mRNAs and facilitating their
translation into polypeptides.
● An essential component of the cell’s division machinery.
● Cytoskeletal elements make up the apparatus
responsible for separating the chromosomes during
mitosis and meiosis and for splitting the parent cell into
two daughter cells during cytokinesis.

11. ● The cytoskeleton (CSK) is
composed of three well-defined
filamentous structures-
● microtubules, microfilaments,
and intermediate filaments
● which together form an elaborate
interactive network.
● Each of the three filaments is a
polymer of protein subunits with
distinct mechanical properties.

12. ● Microfilaments are solid, thinner structures composed
of the globular proteins- actin.
● Microtubule are rigid tubes composed of subunits of the
globular protein- tubulin.
● Intermediate filament are tough, rope like fibers
composed of a variety of related proteins.

13. Although the components of the cytoskeleton appear
stationary, in reality they are highly dynamic structures
capable of rapid and dramatic reorganization

14. Microfilaments
Composition: polymerized chains of the
protein: actin
Location: mostly near the plasma
membrane
Functions:
● Protect cells from physical force
● Facilitate cellular movement (with
myosin and ATP)
● Play a crucial role in cytokinesis (cell
division)

15. ● Actin can be present as
either
a free monomer called G-
actin (globular) or as part of
a polymer microfilament
called F-actin ("F" for
filamentous).
● Actin must be bound to ATP
in order to assemble into its
filamentous form and
maintain the structural
integrity of the filament.

16. ● The actin filament itself has structural polarity
Polarity here refers to the fact that there are two distinct ends to
the filament.
These ends are called the "(-)" end and the "(+)" end.
At the "(+)" end, actin subunits are adding onto the elongating
filament and at the "(-)" end, actin subunits are disassembling or
falling off of the filament.
This process of assembly and disassembly is controlled by the ATP
to ADP ratio in the cytoplasm.

18. ● Protect cells from physical
force

19. ● Facilitate cellular movement (with myosin and ATP)

20. ● Play a crucial role in cytokinesis (cell division)

21. Intermediate filaments
Composition: made of filamentous
proteins
Location: dispersed throughout a cell
Functions:
● Provide structural support to cells
● Withstand tension, making cells
more rigid
● Help keep organelles in place

22. Various types of intermediate filaments

23. Provide structural support to cells

24. ● Help keep organelles in place

25. Microtubules
Composition: hollow tubes made of strings of
tubulin protein
Location: distributed throughout the cytoplasm
Functions:
● Provide structure to the interior of the cell
● Create a network of pathways for
transporting materials (with kinesin and
dynein proteins)
● Assist in organizing a cell's microtubule
network with centrosomes and centrioles
● Crucial for cell division and chromosome
segregation

26. ● These polymers are made
up of globular protein
subunits called α-tubulin
and β-tubulin.
● Both the α-tubulin and β-
tubulin subunits bind to
GTP.
● When bound to GTP, the
formation of the
microtubule can begin,

27. ● As more GTP tubulin dimers assemble onto the
filament, GTP is slowly hydrolyzed by β-tubulin to
form GDP.
● Tubulin bound to GDP is less structurally robust and
can lead to disassembly of the microtubule.

28. ● Provide structure to the interior of the cell

29. ● Create a network of pathways for transporting materials (with
kinesin and dynein proteins)

30. ● Assist in organizing a cell's microtubule network with
centrosomes and centrioles

31. Centrosomes and Centrioles
Composition: made up of nine
microtubule triplets
Functions:
● Organize the cell's microtubule
network
● Crucial for cell division and
mitotic/meiotic spindles

32. ● centrosomes, structures that act as microtubule organizing
centers in animal cells.
● A centrosome consists of two centrioles oriented at right
angles to each other, surrounded by a mass of "pericentriolar
material," which provides anchoring sites for microtubules
● The centrosome is duplicated before a cell divides, and the
paired centrosomes seem to play a role in organizing the
microtubules that separate chromosomes during cell
division.

34. ● Crucial for cell division and chromosome segregation

36. Microtubules radiating from centrale of eukaryotic cell

37. Motile structures (cilia and flagella)
Composition: nine pairs of microtubules
with two microtubules running through
the middle
Functions:
● Cilia: move materials on the surface
of the cell
● Flagella: allow an entire cell to move

38. there are 9 pairs of microtubules
arranged in a circle, along with an
additional two microtubules in the
center of the ring. This
arrangement is called a 9 + 2 array
motor proteins called dyneins
move along the microtubules,
generating a force that causes the
flagellum or cilium to beat.

41. Thank you