Cytoskeleton Microtubules Mind Map PDF

**Definition**:The cytoskeleton is a dynamic and...

**Definition**:The cytoskeleton is a dynamic and flexible network of protein filaments that permeates the cytoplasm of eukaryotic cells Example: **Taxol (Paclitaxel)**. Organization of the cytoplasm. 1. **Stabilizing Agents**: Binds microtubules, preventing **Functions**: Cell shape and structural support. depolymerization. **Chemotherapy Targets**: Facilitation of cell movements. Examples: **Vinca alkaloids** (e.g., Vincristine, Vinblastine). 2. **Destabilizing Agents**: Diameter: ~10 nm. Prevent polymerization of tubulin dimers. Microtubules in Cancer Therapy Cytoskeleton Overview **Intermediate Filaments**: Rope-like fibers structure. They are more stable Disrupts mitotic spindle formation. **Effect**: Provides mechanical strength and stability to cells Blocks mitosis and induces apoptosis in cancer cells. Diameter: ~25 nm. Hollow cylinders (13) made of tubulin dimers. Cilia and flagella are projections of the plasma membrane supported by microtubules **Microtubules**: Rigid and dynamic. They are nucleated **Cilia**: Involved in particle movement over cell surfaces Role: Involved in intracellular transport, cell (e.g., mucus transport in the respiratory tract) **Types of Filaments**: division (spindle formation), and structural support **Active phase**: Dynein arms slide adjacent Diameter: ~7 nm. **Function**: microtubules. **Motion**: Helical polymers of actin. **Recovery phase**: Cilium returns to original **Actin Filaments (Microfilaments)**:  position. Concentrated in the cell cortex (peripherie of the cell) **Flagella**: Enable locomotion of individual cells (e.g., sperm cells) Role: Shape, motility, intracellular transport.  Core structure of cilia and flagella Cilia and Flagella The three filament types are interconnected by accessory A-microtubule: Complete (13 protofilaments) proteins, allowing coordination and integration of their functions Axoneme: B-microtubule: Incomplete (10 protofilaments, 9 peripheral doublets (A and B microtubules) sharing 3 with A) Hollow tubes of variable length. Link adjacent microtubule doublets, preventing Composed of a 9+2 arrangement: Nexin bridges: Composed of **13 protofilaments** arranged in sliding and converting dynein movement into bending **Basic Structure**: a ring-like structure **Structure**: 2 central singlet microtubules Each tubulin dimer binds to GTP for its Made of α-tubulin and β-tubulin dimers. polymerization Attached to A microtubules and generate motion by walking along neighboring B **Plus (+) end**: Rapid growth, directed toward microtubules Microtubules: Structure and Dynein arms: the cell periphery. Organization **Polarity**: ATP hydrolysis drives this motor action **Minus (-) end**: Depolymerizes rapidly, anchored to the centrosome (MTOC) Stable MTs (e.g., cilia and flagella). Regulate microtubule length. ** 2 Types of MTs**: Labile MTs (e.g., mitotic spindle).  Connect microtubules to each other or to other structures. **Functions**: Microtubule stability Initiated by **γ-tubulin ring complex (γ-TuRC)** (Gamma tubuline ring complex) Their is 13 wich will Cytoskeleton: 1. **Nucleation**: at the centrosome. serve for initiation of each 13 protofilaments Enable intracellular transport.  Microtubules Mind Tubulin-GTP binds, adding dimers to the α-tubulin binds to β-tubulin, forming dimers MAP2: Extends long projecting arms, spacing microtubules apart Map 2. **Polymerization**: protofilament. Example: MAP2 and Tau GTP cap at the (+) end stabilizes growth. Tau: Shorter arms, organizes microtubules more **Steps**: closely together Bind along the microtubule lattice to enhance GTP on β-tubulin hydrolyzes to GDP post- stability and suppress depolymerization assembly. Other eg: XMAP215: = A stabilizing MAP that Microtubule-Associated Proteins promotes rapid growth by delivering tubulin (MAPs) 1. **Stabilizing MAPs**: dimers to the plus (+) end 3. **Hydrolysis**: Result: Longer and less dynamic microtubules Promote microtubule shrinkage by disrupting their structural integrity The stability of the microtubule is maintained by a GTP cap at Microtubule Assembly the plus (+) end. If the cap is lost, depolymerization ensues Eg: Kinesin-13 (a catastrophe factor) pulls 2. **Destabilizing MAPs**: apart protofilaments at microtubule ends Result: Shorter and more dynamic microtubules **Types**: Permits transport of organelles, vesicles, and other cellular cargo along microtubules Polymerization occurs when tubulin-GTP concentration > GTP hydrolysis rate concentration of tubulin-GTP dimers **Regulation**: determines polymerization vs. depolymerization. Depolymerization occurs when tubulin-GTP Kinesins: Move cargo toward the plus (+) end concentration < GTP hydrolysis rate  Examples: 3. **Motor MAPs**: Dyneins: Move cargo toward the minus (-) end Motor proteins are crucial for intracellular transport, mitosis, and positioning of organelles like the Golgi apparatus A phenomenon where tubulin dimers are added at **Treadmilling**: the plus (+) end and removed at the minus (-) end, maintaining a constant microtubule length The primary microtubule-organizing center (MTOC) in animal cells Contains 2 perpendicular centrioles surrounded by **Structure**: a dense matrix called pericentriolar material Centrioles are composed of 9 triplets of microtubules arranged in a 9+0 pattern (9T+0) Dynamic Behavior Centrosome Interphase cell ciliated cell Different with the type of cell **Functions**: Catastrophe: Transition from polymerization dividing cell to depolymerization due to the loss of the GTP cap Eg of microtubules searching for chromosomes when cell division. nerve cell Microtubules undergo cycles of growth and Rescue: Growth resumes when tubulin-GTP **Dynamic Instability**:  shrinkage: subunits are added (This dynamic behavior allows the cytoskeleton to reorganize rapidly in response to cellular needs)