Lesson 4. Cytoskeleton, The Sarcomere As An Example PDF

C3 Cytoskeleton © Copyright Universidad Europea. Todos los derechos reservados 1  Index  Cytoskeleton Overview  Actin Microfilaments  Structure...

C3 Cytoskeleton © Copyright Universidad Europea. Todos los derechos reservados 1  Index  Cytoskeleton Overview  Actin Microfilaments  Structure  Functions  Intermediate filaments  Structure  Functions  Microtubules  Structure  Functions  Junctional complex © Copyright Universidad Europea. Todos los derechos reservados 2  Cytoskeleton Link to video Functions: Cell shape Internal organization Cell movement Mechanical strength © Copyright Universidad Europea. Todos los derechos reservados 3  Components CYTOSKELETON ACTIN INTERMEDIATE MICROTUBULES MICROFILAMENTS FILAMENTS (25 nm) (7 nm) (8-10 nm) © Copyright Universidad Europea. Todos los derechos reservados 4 4 (2)  Filaments distribution Actin microfilaments Intermediate filaments Microtubules  Highly concentrated in the  Across the cytoplasm (mechanical  Radially distributed, cortex, beneath the plasma strength) emerging from the membrane (shape) microtubule organizing  Beneath the nuclear membrane center (MTOC). (Cell division, (nuclear protection) transport inside the cell)  Inside cillia and flagella (movement) © Copyright Universidad Europea. Todos los derechos reservados 5 5 (2)  Cytoskeleton distribution © Copyright Universidad Europea. Todos los derechos reservados 6  Actin microfilaments CYTOSKELETON ACTIN INTERMEDIATE MICROTUBULES MICROFILAMENTS FILAMENTS (25 nm) (7 nm) (8-10 nm) © Copyright Universidad Europea. (2)Todos los derechos reservados 7 7  Actin microfilaments  Monomers of G-actin assemble into a helix-shaped thread called F-actin.  Monomers can attach (+ end) or detach (- end) from the polymer Link to video G actin F actin Polarized structure - end + end (1) G actin F actin (monomer) Ca2+ (polymer=thread) ATP Polymerization-depolymerization: Dynamic assembly © Copyright Universidad Europea. Todos los derechos reservados 8  Actin microfilaments In non-muscle cells: 1. Cell shape 2. Microvilli 3. Cytokinesis contractile ring Platelet activation © Copyright Universidad Europea. Todos los derechos reservados 10  Actin microfilaments In non-muscle cells: 4. Actin cytoskeleton from adjacent cells bind through “adherens belts” © Copyright Universidad Europea. Todos los derechos reservados 11  Actin microfilaments In muscle cells: contraction Actin filaments are part of the sarcomere (functional and structural unit of striated muscle) © Copyright Universidad Europea. Todos los derechos reservados 12  Actin microfilaments In muscle cells: contraction Actin filaments move over other filaments (myosin), producing muscle contraction © Copyright Universidad Europea. Todos los derechos reservados 13  Actin microfilaments: functions Summary © Copyright Universidad Europea. Todos los derechos reservados 14  Intermediate filaments CYTOSKELETON ACTIN INTERMEDIATE MICROTUBULES MICROFILAMENTS FILAMENTS (25 nm) (7 nm) (8-10 nm) © Copyright Universidad Europea. (2)Todos los derechos reservados 15 1  Intermediate filaments  Ropelike fibers of long strands of proteins twisted together  No energy is required for polymerization © Copyright Universidad Europea. (2)Todos los derechos reservados 16  Intermediate filaments Strands of different proteins (depending on the cell) Epithelial cells: keratin Muscle cells: desmin Neurons: neurofilaments Characteristics Very stable Resistant to temperature changes © Copyright Universidad Europea. (2)Todos los derechos reservados 17  Intermediate filaments Functions: provide mechanical strength 1. Desmosomes 2. Hair and nails 3. Nerve axons © Copyright Universidad Europea. (2)Todos los derechos reservados 21 2  Intermediate filaments Functions: provide mechanical strength 4. Myosin anchoring in the sarcomere (Z-disc) INTERMEDIATE FILAMENTS (desmin) ACTIN © Copyright Universidad Europea. (2)Todos los derechos reservados 22 2  Microtubules CYTOSKELETON ACTIN INTERMEDIATE MICROTUBULES MICROFILAMENTS FILAMENTS (25 nm) (7 nm) (8-10 nm) © Copyright Universidad Europea. (2)Todos los derechos reservados 23 2  Microtubules Structure  Hollow tubes of about 25 nm  Subunits: dimers of α-tubulin + β-tubulin  Binding of dimers  Protofilament  Binding of 13 protofilaments => MICROTUBULE © Copyright Universidad Europea. Todos los derechos reservados (2) 24  Microtubules STRUCTURE Polymerization requires energy GTP Polarized structure (1) Dimers Protofilament GTP Polymerization-depolymerization: Dynamic assembly © Copyright Universidad Europea. Todos los derechos reservados 25 2  Microtubules FUNCTIONS MT emerge from the MTOC (MT organizing center) (- end) and grow towards the cell membrane (+end) + + + + -- - + + - - - + + + + 1. Vesicles and organelles trafficking (motor proteins required) 2. Mitotic spindle 3. Movement of cilia and flagella © Copyright Universidad Europea. Todos los derechos reservados 27  Microtubules 1. VESICLE AND ORGANELLES TRANSPORT ATP needed Motor proteins Kinesin: towards + end Dynein: towards - end (2) © Copyright Universidad Europea. Todos los derechos reservados 28  Coast Microtubules “hacia la Costa: cinesina” Towards de Coast: kinesin + + + 1. VESICLE AND ORGANELLES TRANSPORT - + + Kinesin  + end  towards plasma membrane Dynein  - end  towards MTOC © Copyright Universidad Europea. Todos los derechos reservados 30  Microtubules 2. MITOTIC SPINDLE (29) © Copyright Universidad Europea. Todos los derechos reservados 35  Microtubules 3. MOVEMENT OF CILIA AND FLAGELLA (29) © Copyright Universidad Europea. Todos los derechos reservados 36  Microtubules 3. MOVEMENT OF CILIA AND FLAGELLA (29) © Copyright Universidad Europea. Todos los derechos reservados 37  Cytoskeleton © Copyright Universidad Europea. Todos los derechos reservados 42  Cytoskeleton JUNCTIONAL COMPLEX Structure formed between 2 adjacent cells Consists of 3 components: tight junction + adherens junction + desmosome (3) (3) © Copyright Universidad Europea. Todos los derechos reservados 43  Cytoskeleton 1. TIGHT JUNCTIONS 1 Seal cells to prevent molecules from leaking No intercelular space 2. ADHESION BELTS 2 Attach adjacent cells through their MF cytoskeleton Bound to actin filaments 3. DESMOSOMES Attach adjacent cells through their IF 3 cytoskeleton Anchored to intermediate filaments © Copyright Universidad Europea. Todos los derechos reservados 45  REFERENCES 1. ALBERTS B et al, Molecular Biology of the Cell, 6ª ed, Editorial Garland Science, 2015. 2. LODISH H et al, Moleculas Cell Biology, 7ª ed, Editorial W. H. Freeman, 2013. 3. SILVERTHORN DU et al, Human physiology: an integrated approach, 7ª ed, Editorial Pearson, 2015. 4. KARP G, Biología Celular y Molecular, 5ª ed, Editorial McGraw Hill, 2009. 1 2 3