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CYTOSOL AND CYTOSKELETON
CYTOSOL fluid part of the cell
cytoplasm Components water ions enzymes
inclusion bodies
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CYTOSKELETON 3 classes of fibres 1./ actin
microfilaments (7 nm) 2./ intermediate filaments
(10 nm) 3./ microtubules (25 nm) Functions main
tainance of the cell shape take part in the
cell motility serve as anchoring points
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ACTIN MICROFILAMENTS I. They play a role in
every type of cell motility. Types a- actins (3
subtypes) non-muscle b-actin non-muscle
g-actin g-actin in intestinal smooth
muscle States of actin globular (G)
actin ATP-G-actin (predominant) ADP-G-actin
Fibrillar (F) actin ATP-F-actin ADP-F-actin
(predominant) Organization of actin
cytoskeleton bundles of filaments networks of
filaments planar 3-dimensional
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Actin (green) and mitochondria (orange) in a
fibroblast cell
Molecular structure of a G-actin molecule
Organization of G-actin
into F-actin molecular complex
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ACTIN MICROFILAMENTS II. Actin cross-linking
proteins short fimbrin, a-actinin
(bundles) long filamin, spectrin, dystrophin
(networks) Polymerization of actin filaments 3
phases lag phase formation of a
nucleus growth phase elongation of the
nucleus equilibrium between the amounts of G-
and F-actin
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• MYOSIN
• Motor protein, or mechanochemical enzyme.
• Types and functions
• 1./ Myosin I. cytoskeleton-membrane interactions
• 2./ Myosin II. muscle contraction and
  cytokinesis
• 3./ Myosin V. cytoskeleton-membrane interactions
• Parts head actin- and ATP binding sites
• neck regulation of the activity of
  the head
• tailbinding sites determining the
  formation of a dimer
• Function
• contraction in muscle cells
• stress fibres in non-muscle cells
• stiffen cortical membranes
• take part in cytokinesis

Light chains
Heavy chains
Heads
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ACTIN-MYOSIN INTERACTION
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MICROTUBULES I. Structure a- and b-tubulins form
heterodimers heterodimers form
protofilaments protofilaments form a
microtubule Cytoplasmic microtubules stable,
long-lived dynamic, short-lived Microtubule
dynamics they can oscillate between growing and
shortening dynamic instability
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MICROTUBULES II. Microtubular cell
organelles cilia, flagella, basal body,
centrioles
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Basal body, centriole
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MTOC microtubule organizing center
amorphous cytosol centrioles g-tubulin pericent
rin centrioles g-tubulin pericent
rin
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• INTERMEDIATE FILAMENTS
• They are smaller than microtubules, but larger
  than microfilaments
• They are present in all eukaryotic cells
  (epithelial cells and neurons
• contain the most)
• They are key determinants of cellular structure
• Functions
• To reinforce cells
• To organize cells into tissues
• Main properties
• Stability
• Assembly of a-helical rods
• Do not bind nucleotides

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Types 1./ Keratins interconnect adjacent
epithelial cells 2./ Neurofilaments form the
core of long axons
1./
2./
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3./ Glial filaments present in
astrocytes 4./ Vimentin in fibroblasts and
adipocytes
3./
4./
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Desmin connect adjacent Z-disks in muscle cells
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Intermediate filaments can be useful in the
diagnosis of cancer. Tumour cells loose their
character and it is difficult to establish their
origin. The identification of one of the
intermediate filaments can identify their
epidermal, neuronal, glial, or mesenchymal
origin.