1. CYTOSOL AND CYTOSKELETON CYTOSOL: fluid part of the cell cytoplasm Components:water ionsenzymes inclusion bodies

2. CYTOSKELETON 3 classes of fibres: 1./ actin microfilaments (7 nm) 2./ intermediate filaments (10 nm) 3./ microtubules (25 nm) Functions:maintainance of the cell shape take part in the cell motility serve as anchoring points

4. ACTIN MICROFILAMENTS I. They play a role in every type of cell motility. Types:  - actins (3 subtypes) non-muscle  -actin non-muscle  -actin  -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

5. 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

6. ACTIN MICROFILAMENTS II. Actin cross-linking proteins: short: fimbrin,  -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

7. 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 neck: regulation of the activity of the head tail:binding sites determining the formation of a dimer tail:binding sites determining the formation of a dimerFunction: contraction in muscle cells contraction in muscle cells stress fibres in non-muscle cells stress fibres in non-muscle cells stiffen cortical membranes stiffen cortical membranes take part in cytokinesis take part in cytokinesis Heads Light chains Heavy chains

8. MICROTUBULES I. Structure:  - and  -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

9. MICROTUBULES II. Microtubular cell organelles: cilia, flagella, basal body, centrioles

10. Basal body, centriole

11. MTOC: microtubule organizing center: amorphous cytosol centrioles  -tubulin pericentrin centrioles g-tubulinpericentrin

12. 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 neuronsThey are present in all eukaryotic cells (epithelial cells and neurons contain the most) They are key determinants of cellular structureThey are key determinants of cellular structureFunctions: To reinforce cellsTo reinforce cells To organize cells into tissuesTo organize cells into tissues Main properties: StabilityStability Assembly of  -helical rodsAssembly of  -helical rods Do not bind nucleotidesDo not bind nucleotides

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

14. 3./ Glial filaments: present in astrocytes 4./ Vimentin: in fibroblasts and adipocytes 3./4./

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

16. 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.