Cell Motors Flashcards
the cytoskeleton is mae up of what 3 things
microtubules, microfilaments, and
intermediate filaments
actin filaments can form?
filopodia, lamellipodia,
microvilli, stress fibers
what are motor proteins
molecular motors that bind to a polarized cytoskeletal filament
and use the energy derived from repeated cycles of ATP hydrolysis to move steadily
along it
what is the purpose of myosins
cause cytoskeletal filaments to slide against each other, generating the force
that drives muscle contraction
what is the function of kinesins and dyneins
carry membrane-enclosed organelles to their appropriate
locations in the cell.
Dyneins are responsible for ciliary beating and flagellar waves.
what are microtubules
hollow rods for: - shaping the cell – guiding movement of organelles – separating chromosomes during cell division - they grow out from a centrosome (MTOC)
what is the centrosome?
it is the MTOC, has a pair of centrioles which each have 9 triplets of microtubules
what are microfilaments
- solid rods, built as a twisted double chain of actin subunits. Function is to bear tension. They form a cortex to support cell shape. They make up microvilli
what are intermediate filaments?
- fibrous proteins supercoiled into thick cables
- proteins are of the keratin family
- maintain cell shape, anchor nucleus and organelles, form nuclear lamina
cytoskeleton filaments are x and y
dynamic and adaptable
give examples of self assembled structures
cytoskeleton filaments, virus coats,
bacterial flagella, protein machines. Also, pathogenic protein aggregates
(hemoglobin-S polymers, prions, Alzheimer’s plaques)
what is a polar filament?
Each asymmetric subunit points in the same
direction (orientation). The two ends are topologically different, therefore
the resulting filament lattice has inherent directionality.
what is a non polar filament
Polypeptides are always asymmetric, but they
can polymerize into filaments where both ends of the composing
subunits are topologically equivalent, therefore the resulting lattice has
no inherent directionality
what are the implications of filament polarity?
Proteins that bind a filament will adopt the same orientation(Only polar filaments can act as directional tracks for motor proteins) Different protein surfaces are exposed at the two ends – End-specific nucleation – End-specific capping
what is the preferred end for subunit addition of microtbules
+ end
what structure acts as tracks for movement of vesicles?
microtubules, Golgi
and lysosomes move towards minus ends
while secretory vesicles move towards plus ends
what is the preferred end for adding on subunits for actin?
actin filaments are organized
with their barbed ends pointing forwards. As the membrane protrudes,
new actin subunits polymerize onto these barbed ends
What is G-actin?
(globular actin), with
bound ATP, can polymerize to
form F-actin
what is F-actin?
may hydrolyze bound ATP ADP + Pi and release Pi ADP is not released from the filament because the nucleotide binding pocket is closed in Factin.
what is the purpose of G-actin?
can release ADP and bind ATP, which
is usually present at higher concentration than ADP in the cytosol.
the cleft of actin monomers faces
towards the minus end
actin filaments may undergo treadmilling, which is?
in which filament length remains approximately constant, while actin monomers add at the (+) end and dissociate from the (-) end.
what are the 3 groups of actin binding proteins?
banding and cross-linking proteins
regulatory proteins, motor proteins (myosin)
give examples of regulatory protein
Profilin: controls turnover of the G actin pool
Thymosin b4: regulates actin polymerization by sequestering G actin subunits
Formin: assists actin polymerization in cooperation with profilin
Tropomodulin: Prevents dissociation
of the filament into
monomer subunits
what is the function of actin-binding proteins such as a-actinin, villin and fimbrin
bind
actin filaments into parallel bundles.
filamins dimerize to form
V shaped cross-linking proteins that
are inherently flexible, organize actin filaments
into loose networks, may also have scaffolding roles
structure of myosin II
two heavy chains acids long and four light chains, The light chains are of two distinct types, and one copy of each type
is present on each myosin head. Dimerization occurs when the two
α helices of the heavy chains wrap around each other to form a
coiled-coil, driven by the association of regularly spaced
hydrophobic amino acids. The coiled-coil arrangement makes an
extended rod in solution, and this part of the molecule is called the
tail
myosin V is involved in
vesicle and organelle transport
kinesins walk towards
the + end of a microtubule
what are dyenins
minus-end-directed microtubule motors,
what are the 2 kinds of dyenins?
cytoplasmic dyneins, which are
typically heavy-chain homodimers, with two large motor domains as heads. Cytoplasmic dyneins are probably found in
all eucaryotic cells, and they are important for vesicle trafficking, as well as for localization of the Golgi apparatus near
the center of the cell.
Axonemal (ciliary) dyneins, the other large branch, include heterodimers and heterotrimers, with two or three motordomain heads, respectively. They are highly specialized for the rapid and efficient sliding movements of microtubules
that drive the beating of cilia and flagella.
can dyenin act on its own?
it need accessory proteins, like actin-related protein Arp1, spectrin and ankyrin
what is the common structure of cilia and flagella
a core of microtubules sheathed by the plasma membrane
– a basal body that anchors the cilium or flagellum
– dynein, which drives the bending movements of a cilium or
flagellum
