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Centrosomes & Centrioles (Microtubules grow out from centrosomes…
Centrosomes & Centrioles
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Outer wall of centriole cylinder is 9 triplets MTs - A-tubule (complete) fused with B & C-tubules (incomplete)
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Centrioles
- Cylindrical structures
- Found in pairs - right angles to each other
- Each wall made of nine interconnected triplet microtubules
- Centriolar more stable that cytoplasmic
- Duplicates once each cell cycle
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Spindle Apparatus
- Microtubules for spindles apparatus - vital for organisation of cellular contents during cell division
- Mitotic spindle structure forms during cell division and separates duplicated chromosomes.
- Ensure they are equally divided among 2 daughter cells.
Molecular Motors
- Move materials from one place to another in the cytoplasm
- Moved using vesicles loaded with cargo that can move along the cytoskeleton
- Example - nerve cell with an axon
Motor proteins
- Bind to polarised cytoskeletal filament
- Associate with filament tracks through 'head' region or motor domain that binds and hydrolyses ATP
- Coordinated with cycle of nucleotide hydrolysis and conformational change.
- Proteins cycle between states
- Bound strongly to their filament tracks which they are unbound
Guiding movement of organelles
- Function as the track in the intracellular transport of membrane-bound vesicles and organelles
- Identity and direction of track movement determined motor domain head
- Identity of cargo determined by tail of motor protein
- KINESIN and DYNEIN - motor proteins associated with vesicle/organelle movement
- Move in opposite directions
- Kinesin towards the plus ends
- Dinesin toward the minus ends
Microtubules in flagella and cilia
- 9+2 arrangement through their cross section
- Cell possess one or two long flagella. Ciliated cells have many short cilia
Intermediate Filaments
- Diameter 8-12 nanometers
- Larger than microfilaments
- Smaller that microtubules
- a-helical proteins divided into 6 major classes or types
- The expression of each one is characteristic of a certain tissue or cell type.
Intermediate Filament Functions
- Maintenance of cell shape - tension bearing elements
- Anchorage of nucleus and other organelles
formation of nuclear lamina
- Link to extracellular matrix
Actin Filaments
- Most dynamic of the 3
- They grow, shrink and change conformation
- Provide mechanical support
- Connect contents of cytoplasm with cell membrane - supports signal transduction
- Vesicle and organelle moved along microfilament tracks - controlled cargo transport myosins V & VI
- Made up of identical actin proteins
- Arranged in long spiral chain
-Considered to have polarity
- 7nm in diameter
- Twisted double chain of actin subunits
- Structural role - bear tension, resisting pulling forces within cell.
- Form 3D cortex inside plasma membrane - support cells shape
Actin Filaments Functions
- Maintain cell shape
-Changes in cell shape
- Muscle contraction
- Cytoplasmic streaming
- Cell motility
- Cell division
Cytoskeleton Summary
- Network of insoluble protein fibres throughout cytoplasm.
- Organises contents of the cell
- Connects the cell physically and biochemically to the external environment
- Enables cell to move and change shape
- Dynamic, motor proteins can transport vesicle and organelles around the cell.