Lecture 6: Cytoskeleton Flashcards
What are the main types of proteins that make up the cytoskeleton?
Microfilaments (actin)
Intermediate filaments
Microtubules
What are the characteristics of actin?
Diameter: 7nm
Organization: bundles and 3D networks
Bind directly or indirectly to transmembrane protein.
What is monomer of actin called?
G-actin (globular)
What is polymerized actin called?
F-actin (filamentous)
Describe the polarity of an actin filament
Barbed end (positive end): growth occurs more rapidly
Pointed end (negative end): disassembly occurs more rapidly
Describe what happens to an actin filament at high, intermediate, and low cytoplasmic concentrations.
High concentrations favors actin filament growth.
Intermediate concentrations result in a dynamic equilibrium between growth and disassembly at the barbed and pointed end respectively; TREADMILLING
Low concentrations favor actin filament disassembly
What does cytochalasin do?
Binds the barbed end of actin and prevents elongation.
What does phalloidin do?
Binds to actin filaments at different parts and prevents dissociation.
What does spectrin do?
Binds the cortical cytoskeleton to the plasma membrane in RBCs.
What does dystrophin do?
Binds the cortical cytoskeleton to the plasma membrane.
What do villin and fimbrin do?
Forms cross linkages in microvilli.
What do calmodulin and myosin I do?
Forms cross-linkages between actin and plasma membrane inn microvilli.
What does alpha-actinin do?
Forms cross linkages in stress fibers and connects to protein plasma membrane complexes.
What does filamin do?
Forms cross-linkages in actin to for a screen-like gel.
What does thymosin do?
Captures actin monomers; prevents polymerization.
What does profilin do?
Binds monomers and facilitates exchange of ADP for ATP.
What does gelsolin do?
Caps actin filaments and destabilizes it. Fragments the filament in high concentration of calcium.
What does cofilin do?
Disassembles ADP actin at the pointed end.
What does arp2/3 do?
Initiates growth on the sides of actin filaments; causes branching.
What do latrunculins do?
Bind G-actin inducing F-actin depolymerization.
What are the characteristics of intermediate filaments
Diameter: 8-10nm
Provides tensile strength.
Form cytoplasmic network.
Scaffolding to organize internal structures.
What is the structure of an intermediate filament?
Two polypeptides from a coiled dimer.
Dimers assemble in a staggered antiparallel fashion to form a tetramer.
Tetramers align end to end to form protofilaments.
Eight protofilaments are wound together to form a filament.
What are the structure of a microtubule?
- dimer of alpha and beta tubulin
- dimers line up to form protofilaments
- 13 protofilaments form a hollow cylinder, microtubule
- 25 nm
Describe how microtubules assemble.
- assembly is more rapid on the plus end and slower on the minus end
- tubulin-GTP is added to the plus end and hydrolyzed
- exhibits treadmilling
