Lecture 22 Flashcards
What is the relationship between kinesin and dynein in Zebrafish embryos
Survival method used for camouflage
Melanin granules are dispersed outward by kinesin and cause the embryo to be darkly coloured
Melanin granules are brought toward the center by dynein to make the embryo to be lightly coloured
What are the functions of microfilaments?
Maintenance of cell shape
Cell movement
Vesicle transport
Muscle contraction (tissue movement/contraction, happens all at once)
Cytokinesis (contractile ring)
Describe the structure of microfilaments
Thinnest cytoskeletal element (~8nm)
Polymer of actin protein
Actin acts as a monomer (G-actin or globular actin) or as a polymer (F-actin or fibrous actin)
What is the structure of G-actin?
Has 4 subdomains
Divided by the central cleft that creates 2 almost equal-sized lobes
What is the structure of an F-actin unit?
Made of 2 strands of G-actin monomers.
One F-actin unit has 28 subunits of G-actin and is 72 nm in length
Are microfilaments polar like microtubules
Yes, F-actin filament have a plus and minus end
Plus end: assembles/disassembles quickly
Minus end: assembles/disassembles slowly
What is Phalloidin?
A toxin in the phallotoxin family
Found in death cap mushrooms and is lethal once it reaches the bloodstream
The toxin binds to and stabilizes F-actin and prevents the depolymerization of actin fibers
Describe the arrangement/assembly of F-actin microfilaments
What substance regulates the assembly?
Arranged in a loose array network (meshwork) or in tight bundles/cables/fibers
actin-binding proteins regulate the organization structure
What are myosins? What direction do they move in?
Myosins: superfamily of motor proteins associated with microfilaments and actin
They move toward the “+” end of the microfilaments
What are the 2 groups of myosins? What are their functions?
Conventional myosins: primary motors for muscle contraction,Type II (diagram on slide 22)
Unconventional myosins: orangelle/vesicle movement
Type I and types III-XVIII (diagram on slide 22)
What is the function of unconventional myosins, actin and regular myosins in relation to non-muscle cell functions
Unconventional myosins: generates force and contribute to motility in non-muscle cells
Actin: protrusion (push) of leading edge (lamellipodium) powered by action growth
Myosin: contraction pulls the trailing edge forward (to extend the cell)
What function do microtubule-based and microfilament-based motors both share
They work together in intracellular transport
Kinesin transfers vesicle to myosin motor protein to move it to it’s final destination
Describe the structure of intermediate filaments (IF)
What is their only function?
~10nm in diameter
Only found in multicellular animal cells
Stable compared to MTs of MFs
Arrangement of fibrous alpha-helical proteins
Not polar (IFs are not used for transport)
Function: provides structural support and mechanical strength
What are some examples of intermediate filaments (IFs)
Keratins: epithelial cells (in cytoplasm)
Neurofilaments: neuron-specific
Lamins: nucleus of cells
Where are intermediate filaments most abundant
In the axons of neurons (neurofilaments)
