microtubles

1. SEMINAR
ON
MICROTUBULES AND MICROFILAMENT
SUBMITTED BY
MR. AHMAD ALI
M.Sc. ZOOLOGY (Sem. II)
SUBMITTED TO
DR S.R.AKARTE
HEAD
OF THE DEPARTMENT ZOOLOGY
VIDYABHARATI MAHAVIDYLAYA, AMRAVATI.
2012-2013

2. IndexIndex• Microtubules
• Structure of microtubules
• Chemical composition of microtubules
• Microtubules in cilia and flagella
• Microtubules in cell division
• Motor proteins in membrane traffic
• Functions
• Microfilaments
• Actin filaments in muscles cells
• Actin filaments in non muscles cells

3. Microtubules :
Microtubules as the word indicates, are tube
like cylindrical structure which are unbranched
and can be several micron in length. They are
hollow tubes, about (20-30 nm) in diameter..
Microtubules are hollow, tubular structures, and
they occur nearly in all eukaryotic cells.
The first observation of these tubular structures in
the axoplasm was made by De Robertis and
Franchi in 1953.

4. Structure of Microtubules
Microtubules as the word indicates, are
tube like cylindrical structure which are
unbranched and can be several micron in
length. They are hollow tubes, about (20-30
nm) in diameter. These microtubules
consists of a circular array of 13 subunits
called as protofilaments. These subunits
are globular in shape and are 5-7 nm in
diameter.

6. Chemical composition and assembly :
The chemistry of microtubules has been studied in some
detail with the help of colchicines and its derivative colcemide
other chemicals like vincristine, vinblastini and
podophyllotoxin, which inhabit assembly of microtubules.
These chemicals bind to the globular subunit and prevent
polymerization.
Microtubules are composed of a single type of globular
protein called tubulin. Tubulin protein consists of -tubulinὰ
and β tubulin, each with a molecular weight of 60,000 daltons.
The dimeric protein,tubulins polymerize at 370
C (Human body
temperature ) to form characteristic microtubule structure.

9. • Microtubules are the central structural
supports in cilia and flagella.
–Both can move unicellular and small
multicellular organisms by propelling water past
the organism.
–If these structures are anchored in a large
structure, they move fluid over a surface.
• For example, cilia sweep mucus carrying trapped
debris from the lungs.
Fig. 7.2

10. • Cilia usually occur in large numbers on the
cell surface.
–They are about 0.25 microns in diameter and 2-
20 microns long.
• There are usually just one or a few flagella
per cell.
–Flagella are the same width as cilia, but 10-200
microns long.

11. In spite of their differences, both cilia and flagella have
the same ultrastructure.
Both have a core of microtubules sheathed by the
plasma membrane.
Nine doublets of microtubules arranged around a pair
at the center, the “9 + 2” pattern.
Flexible “wheels” of proteins connect outer doublets to
each other and to the core.
The outer doublets are also connected by motor
proteins.
The cilium or flagellum is anchored in the cell by a
basal body, whose structure is identical to a centriole.

13. Microtubules in cell division.Microtubules in cell division.
• After the two centromeres moves towards the opposite sides of the cell at
the beginning of mitosis ,the duplicated chromosome attach to kinetochore
and chromosomal microtubules and align on the metaphase plate.
• The links between chromatids breaks and anaphase begins. Anaphase
consists of movement of chromosome towards the spindle pole along the
kinetochore microtubule, which shortens as the chromosome movement
proceeds.
• Movement of chromosome along the spindle microtubules is driven by
kinetochore-associated motor proteins. Cytoplasmic dynien is associated
with kinetochore The action of these kinetochore proteins is coupled to
disassembly and shortening of both kinetochore and chromosomal
microtubules, which is mediated by kinesins that acts as microtubule-
depolymerizing enzymes.

14. MetaphaseMetaphase
Polar
microtubule
Kinetochore
proteins attached
to centromere Kinetochore
microtubule
Metaphase
plate

15. FigureFigure
9.99.9
Figure 9.9
figure 09-09.jpg
spindle

16. AnaphaseAnaphase
• As anaphase proceeds Kinetochore

17. Motor proteins in membrane traffic :-
Two type of motor proteins. Kinesins and
Cytoplasmic dyneins.
1) Kinesins:- iTs responsible for moving vesicles
and organelles from the cell body toward the synaptic
terminals. This motor protein, which was named,
Kinesin, it constructed from two identical heavy
chains and two light chains.

19. 2)Cytoplasmic Dyneins
iTs responsible for the movements of cilia
and flagella. The protein was named
dynein. It took over 20 years before a
dynein like proteins was purified and
characterized from mammalian brain
tissue.

20. Cytoplasmic dyneins is huge protein composed of
two identical heavy chain and a variety of intermediate
and light chains. Dyneins heavy chain as large globular
head, which acts evidence suggests at least two roles for
Cytoplasmic dynein.
1)A force – generating agent in the movement of
chromosome during mitosis.
2)A minus end-directed microtubular motor for the
positioning of the Golgi complex and the movement of
vesicles and organelles through the cytoplasm.

21. Different components of a dynein motor protein

22. Function :
Microtubules function as -
1) An internal Skeleton that provides structural
support and helps maintain the position of
Cytoplasmic organelles
2) Part of the molecular machinery that moves
materials and organelles from one part of a cell to
another.
3) The motile elements of cilia and flagella.
4) Actin components in chromosome separation
during mitosis and meiosis.

23. Microfilaments,
• the thinnest class of the cytoskeletal fibers,
are solid rods of the globular protein actin.
– An actin microfilament consists of a twisted
double chain of actin subunits.
• Microfilaments are designed to resist
tension.
• With other proteins, they form a three-
dimensional network just inside the plasma
membrane.

24. Fig. 7.26 The shape of the
microvilli in this intestinal
cell are supported by
microfilaments, anchored
to a network of
intermediate filaments.

25. • In muscle cells, thousands of actin filaments are
arranged parallel to one another.
• Thicker filaments, composed of a motor protein,
myosin, interdigitate with the thinner actin fibers.
– Myosin molecules walk along the actin filament,
pulling stacks of actin fibers together and
shortening
the cell.
Fig. 7.21a

26. • In other cells, these actin-myosin aggregates are less
organized but still cause localized contraction.
– A contracting belt of microfilaments divides the
cytoplasm of animals cells during cell division.
– Localized contraction also drives amoeboid movement.
• Pseudopodia, cellular extensions, extend and
contract through the reversible assembly and
contraction of actin subunits into microfilaments.
Fig. 7.21b

27. REFRENCESREFRENCES
2)Cell and Molecular biology2)Cell and Molecular biology
- Gerald Karp- Gerald Karp
3)The cell, A molecular approach3)The cell, A molecular approach
(fifth edition)(fifth edition)
- G.M. Cooper- G.M. Cooper
4) www.google.com4) www.google.com

28. •THANK YOU…