Structure and function

1. MICROFILAMENTS AND
INTERMEDIATE FILAMENTS
Submitted by,
Swathy T
M.Sc. Microbiology
Submitted to,
Jaya Miss

2. CYTOSKELETON
• The cytoskeleton is a complex, dynamic network of
interlinking protein filaments present in the cytoplasm
of all cells.
• The cytoskeleton is responsible for contraction, cell
motility, movement of organelles and vesicles through
the cytoplasm.
• It is a complex network of 3 types of protein filaments
.
• 1) Microtubules
• 2) Microfilaments
• 3) Intermediate filaments

3. MICROFILAMENTS
• Microfilaments are the polymers of the protein actin and are smallest
filaments of the cytoskeleton with diameter of about 5 – 7 nm.
• They are formed of contractile protein actin, myosin, troponin,
tropomyosin etc...
• Actin form major constituent of microfilaments, myosin present in low
conc. And other proteins occur in very small amount.
• Functions: give mechanical support to the cell, involve cell membrane
motility, endocytosis and exocytosis, secretion and vesicle
transfer,changes in cell shape.

4. ACTIN
• Main structural protein of microfilaments.
• Actin exist either in the free monomeric and globular form called G-
actin.
• or in the polymerised , filamentar fibrous form called F-actin.
• They undergo polymerization reaction from G-actin monomer state to
F-actin polymer state.

5. • Treadmiling
• At a critical conc. of G-actin, the
polymerisation and
depolymerisation of F-actin are in
dynamic equilibrium. In such a state,
the rate of the addition of G-actin
monomers at the plus end of the F-
actin is equal to the rate of their loss
from the minus end. As a result, the
length of actin filament remains
almost unchanged. This
phenomenon is called treadmiling

6. MYOSIN
• Myosin molecule is formed of 2 spirally twisted peptide chains. It is
almost rod like , with a globular “head” and a filamentar “tail”.
• The head is called heavy meromyosin (HMM).
• The tail is called Light meromyosin (HMM).
• Head has 2 sub units HMM-S1 and HMM-S2.
• S1 is the most important part and it forms a projecting cross bridge for
binding with actin filament, also contain binding sites for enzyme
ATPase.
• Myosin servers as the “molecular motor” which associates with actin
filaments and provides the force for cell movement.

8. INTERMEDIATE FILAMENTS
Intermediate filaments (IF) are tough and durable protein Fibres in the
cytoplasm of most higher eukaryotic cells.
They are between 8 to 10 nm in diameter, which is Intermediate btw the
thin and thick filaments in muscle cells.
Functions: highly resistant to stress and strains, provide tensile strength
and mechanical stability to cell, more stable than microfilaments and
microtubules, intermediate fibres form network that connect nucleus to
plasma membrane.
It contain N terminal and C terminal of IF proteins. N terminal head
domain binds to DNA.

10. • Different kinds of IFs
• Keratin filament: formed of fibrous protein keratins. They are most
complex type of Ifs. Found in epithelial cells.
• Glial filaments : found in the cytoplasm of some glial cells. They found
only in astrocytes
• Neurofilaments : found in neurons. Together with microtubules they
form the main structural elements of cyton, axon and dendrites.
• Vimentin: is widely distributed in cells of mesenchymal origin
• Desmin: found in both striated and smooth muscle cells.
• Synemin: present in Ifs of muscle, together with vimentin and desmin.

11. THANK YOU