CYTOSOL AND CYTOSKELETONCYTOSOL AND CYTOSKELETON

CYTOSOL: fluid part of the cell cytoplasmCYTOSOL: fluid part of the cell cytoplasmComponents:Components: waterwater

ionsionsenzymesenzymesinclusion bodiesinclusion bodies

CYTOSKELETONCYTOSKELETON

3 classes of fibres:3 classes of fibres:

1./ actin microfilaments (7 nm)1./ actin microfilaments (7 nm)

2./ intermediate filaments (10 nm)2./ intermediate filaments (10 nm)

3./ microtubules (25 nm)3./ microtubules (25 nm)

Functions:Functions: maintainance of the cell shapemaintainance of the cell shape

take part in the cell motilitytake part in the cell motility

serve as anchoring pointsserve as anchoring points

ACTIN MICROFILAMENTS I.ACTIN MICROFILAMENTS I.

They play a role in every type of cell motility.They play a role in every type of cell motility.Types:Types: - actins (3 subtypes)- actins (3 subtypes)

non-muscle non-muscle -actin-actinnon-muscle non-muscle -actin-actin-actin in intestinal smooth muscle-actin in intestinal smooth muscle

States of actin:States of actin:globular (G) actin:globular (G) actin: ATP-G-actin (predominant)ATP-G-actin (predominant)

ADP-G-actinADP-G-actinFibrillar (F) actin:Fibrillar (F) actin: ATP-F-actinATP-F-actin

ADP-F-actin (predominant)ADP-F-actin (predominant)Organization of actin cytoskeleton:Organization of actin cytoskeleton:

bundles of filamentsbundles of filamentsnetworks of filaments:networks of filaments: planarplanar

3-dimensional3-dimensional

Actin (green) and Actin (green) and mitochondria (orange) mitochondria (orange) in a fibroblast cellin a fibroblast cell

Molecular structure of a Molecular structure of a G-actin moleculeG-actin molecule

Organization of G-actinOrganization of G-actin into F-actin molecular complexinto F-actin molecular complex

ACTIN MICROFILAMENTS II.ACTIN MICROFILAMENTS II.

Actin cross-linking proteins:Actin cross-linking proteins:short: fimbrin, short: fimbrin, -actinin -actinin

(bundles)(bundles)long: filamin, spectrin, long: filamin, spectrin, dystrophin (networks)dystrophin (networks)

Polymerization of actin Polymerization of actin filaments:filaments:3 phases: lag phase: formation 3 phases: lag phase: formation

of a „nucleus”of a „nucleus”growth phase: elongation growth phase: elongation of the „nucleus”of the „nucleus”equilibrium between the equilibrium between the

amounts of G- and F-actinamounts of G- and F-actin

MYOSINMYOSIN

Motor protein, or mechanochemical enzyme.Motor protein, or mechanochemical enzyme.Types and functions:1./ Myosin I.: cytoskeleton-membrane interactions1./ Myosin I.: cytoskeleton-membrane interactions2./ Myosin II.: muscle contraction and cytokinesis2./ Myosin II.: muscle contraction and cytokinesis3./ Myosin V.: cytoskeleton-membrane interactions3./ Myosin V.: cytoskeleton-membrane interactionsParts:Parts: head: actin- and ATP binding sites head: actin- and ATP binding sites neck: regulation of the activity of the headneck: regulation of the activity of the head tail:binding sites determining the tail:binding sites determining the formation of a dimerformation of a dimerFunction:Function:• contraction in muscle cellscontraction in muscle cells• stress fibres in non-muscle cellsstress fibres in non-muscle cells• stiffen cortical membranesstiffen cortical membranes• take part in cytokinesistake part in cytokinesis

Heads

Light chains Heavy chains

MICROTUBULES I.MICROTUBULES I.Structure:Structure: - and - and -tubulins form heterodimers-tubulins form heterodimers

heterodimers form protofilamentsheterodimers form protofilamentsprotofilaments form a microtubuleprotofilaments form a microtubule

Cytoplasmic microtubules:Cytoplasmic microtubules: stable, long-livedstable, long-liveddynamic, short-liveddynamic, short-lived

Microtubule dynamics:Microtubule dynamics: they can oscillate between they can oscillate between growing and shortening: dynamic instabilitygrowing and shortening: dynamic instability

MICROTUBULES II.MICROTUBULES II.Microtubular cell organelles:Microtubular cell organelles:

cilia, flagella, basal body, centriolescilia, flagella, basal body, centrioles

Basal body, centrioleBasal body, centriole

MTOC: microtubule organizing center:MTOC: microtubule organizing center:

amorphous cytosolamorphous cytosol

centriolescentrioles

-tubulin-tubulin

pericentrinpericentrin centriolescentriolesg-tubuling-tubulinpericentrinpericentrin

INTERMEDIATE FILAMENTS:INTERMEDIATE FILAMENTS:

•They are smaller than microtubules, but larger than microfilamentsThey are smaller than microtubules, but larger than microfilaments•They are present in all eukaryotic cells (epithelial cells and neurons They are present in all eukaryotic cells (epithelial cells and neurons

contain the most)contain the most)•They are key determinants of cellular structureThey are key determinants of cellular structure

Functions:Functions:

•To reinforce cellsTo reinforce cells•To organize cells into tissuesTo organize cells into tissues

Main properties:Main properties:

•StabilityStability•Assembly of Assembly of -helical rods-helical rods•Do not bind nucleotidesDo not bind nucleotides

Types:Types:1./ Keratins:1./ Keratins: interconnect adjacent epithelial cells interconnect adjacent epithelial cells2./ Neurofilaments:2./ Neurofilaments: form the core of long axons form the core of long axons

1./1./ 2./2./

3./ Glial filaments:3./ Glial filaments: present in astrocytes present in astrocytes

4./ Vimentin:4./ Vimentin: in fibroblasts and adipocytes in fibroblasts and adipocytes

3./3./ 4./4./

Desmin:Desmin: connect adjacent Z-disks in muscle cells connect adjacent Z-disks in muscle cells

Intermediate filaments can be useful in the diagnosisIntermediate filaments can be useful in the diagnosisof cancer.of cancer.

Tumour cells loose their character and it is difficult to Tumour cells loose their character and it is difficult to establish their origin.establish their origin.

The identification of one of the intermediate filaments The identification of one of the intermediate filaments can identify their epidermal, neuronal, glial, or can identify their epidermal, neuronal, glial, or mesenchymal origin.mesenchymal origin.