Cytoskeletal System Flashcards
Cytoskeleton
It is a network of interconnected filaments and tubules extending through the cytosol
-It plays roles in cell movement and division
-It is dynamic and changeable
-Cell interior is highly structured
Cytoplasmic microtubules
-Maintaining axons
-Formation of mitotic and meiotic spindles
-Maintaining or altering cell shape
-Placement and movement of vesicles
-Orientation of cellulose microfibrils during plant cell wall growth
Axonemal microtubules
-Includes the organised and stable microtubules found in structures such as:
-Cilia
-Flagella
-Basal bodies to which cilia and flagela attach
-The axoneme, the central shaft of a cilium or flagellum, is a highly ordered bundle of MTs
Microtubule structure
-Beta tubulin will always be N-terminal end that has a plus end
-Alpha tubulin will always be a C-terminal end that has a negative charge
rate-limitng step of microtubules
formation of dimers is slowest steps
Microtubule assembling
Microtubule Treadmiling
+ and - ends have different critical concentrations
-Treadmiling: addition of subunits at the plus end, and removal from the minus end ( constant elongation and shortening)
Dynamic instability model
One population of MTs grows by polymerisation at the plus ends, whereas another population shrinks by depolymerisation at the plus ends
-GTP gives stability and when there is no GTP, the dimer breaks down at plus end which is known as catastrophe
Catastrophe
-Individual MTs can go through periods of growth and shrinkage; a switch from growth to shrinkage
rescue
A sudden switch back to growth phase
Catastrophe and rescue graph
MTOC
Microtubule organising center
-Gamma tubulin binds to gamma-TuRC and stabilises Mt
MTOC distribution
Anaphase I- Centrosome
Basal body
Centrosomes
Composed of a triplet arrangement with 9 triplet microtubules being used to make a centriole
Colchicine, colcemid
Binds B-tubulin
-inhibitng assembly
Nocadazole
Binds beta-tubulin which inhibits polymerisation
Vinblastine, vincristine
Aggregates tubulin heterodimers
Paclitaxel (taxol)
Stabilises microtubules
-Uses up all tubulin causing cell to die because there is no movement
MTOC different cells
Nerves
Ciliated epithelial
RBC
Mt regulation
-great precision
-Mt-binding proteins use ATP to drive vesicle or organelle transport or to generate sliding forces between MTs
-Others regulate Mt structure
Microfilament functions
-Smallest filaments
1. Muscle contraction
2. Cell migration, amoeboid movement and cytoplasmic streaming
3. Maintenance of cell shape
4. Structural core microvilli
5. Cleavage furrow production during cytokinesis
G-actin
globular actin
single protein
gives rise to f-actin
-Has to be ATP-bound to be attached to filament
F-actin
Filamentous actin
multiple G-actins bound together to form MF (polymerised)
-2 F-actin eind together to form MF
Isoforms
alpha-actin-muscular
Beta-actin
gamma-actin
Polarity of MF
Polarity is reflected in more rapid addition or loss of G-actin at plus end than minus end
-After the G-actin monomers assemble onto MF, the ATP bound to them is slowly hydrolysed
-So growing MF ends have ATP-actin whereas most of MF is composed of ADP-actin
Architecture of Actin in crawling cells
-Rapid moving cells dont have stress fibers
-The cell cortex, just beneath the plasma membrane, has actin crosslinked into a gel of MF
Stress fibers
Cells that adhere tightly to underlying substratum have organised bundles called stress fibers
-found in contractile bundle
Cell cortex
gel
Lamelllpodium
Branched network
Flipodium
Parallel bundle
Actin binding proteins
Control where and how actin assembles into MF
Filament formation binding proteins
Monomer sequestering proteins prevent formation (thymosin)
-Actin polymerising proteins cause formation (formin)
Filament lenght binding proteins
filament-severing proteins (gelsolin)
Filament-capping proteins (CapZ)
Filament organisation actin binding proteins
Filament-crosslinking proteins (filamin)
Filament-bundling proteins ( alpha-actin, fibrinin)
Drugsthat affect stability of MFs
Intermediate filaments
Most stable
least soluble
likely support entire cytoskeleton
IF proteins are tissue specific
-Keratin is NB component of structures that grow on skin in animals
classes of IF
IF formation
Drugs that affect IF stability
Acrylamide- Causes loss of intermediate filament networks (carcinogenic)
IF functions
Critical concentration
The tubular heterodimer concentration at which MT assembly is exactly balanced with disassembly
