14.4 Microtubule Motors and Movement Flashcards
what are the 2 protein motors involved in powering microtubule movement?
- kinesins - move towards plus ends of microtubules
- dyneins - move towards minus ends of microtubules
compare and contrast the general structure of kinesins and dyneins
- both kinesins and dyneins have heavy and light chains
- only dyneins have intermediate chains
motor movement of kinesins and dyneins is powered by ()
ATP
how does ATP allow for kinesin/dynein movement along microtubules
interaction of motor protein globular head domains (motor domains) with ATP causes a conformation change in the head domains, thus allowing them to move along microtubules
experiments (isolation of kinesin) found that in the presence of ATP, motor proteins (i.e. kinesins) ()
interact and release from microtubules
how are kinesins and dyneins involved in cargo transport
- microtubules are usually oriented with their minus ends anchored at the centrosome and their plus ends extending toward the cell periphery
- kinesins usually bring cargo (usually vesicles/organelles) towards cell periphery, where as dyneins usually bring cargo towards the center of the cell
cargo selection can be very specific → dyneins and kinesins recognize different microtubules by the ()
posttranslational modifications of tubulin
which motor proteins are involved in position which membrane-bound organelles in the cell?
- kinesins play a role in positioning and pulling the ER towards cell periphery
- dyneins play a role in positioning the Golgi at the center of the cell
the ER extends to the periphery of the cell through ()
association with microtubules
() are microtubule-based projections of the plasma membrane that are found on almost all types of animal cells
cilia and flagella
() act as antennae that sense a variety of extracellular signals as well as being responsible for movement
cilia
some bacteria have (), but these are protein filaments projecting from the cell surface rather than microtubule-based projections
flagella
() are found on most animal cells and are involved in sensing extracellular signals; they play an important role during development but have no motor function in adults
primary cilia
() are responsible for movement (same with flagella) either across a surface or movement of fluid/mucus across cell surface (e.g. in epithelial cells)
motor cilia
structures of cilia and flagella are similar; both have:
- basal body - where the protrusion (i.e. cilia or flagella) extends from cell body
- axoneme - actual protrusion of cell
describe the structure of the basal body
- centriole containing 9 triplets of microtubules (triplet microtubules)
- derived from centrioles that have been transported to the plasma membrane
- serve to initiate the growth of axonemal microtubules as well as anchor cilia to the surface of the cell
describe the general structure of an axoneme
contains 9 doublet microtubules (two from each of the triplets in the basal body extend into axoneme); contains a complete A tubule (13 protofilaments) and an incomplete B tubule (10-11 protofilaments)
axonemes of motile cilia and flagella contain an additional () and () that are responsible for motility
- central pair of microtubules
- associated proteins
in motor cilia and flagella, doublet microtubules are arranged in a ()
”9+2 pattern” → central pair is surrounded by 9 doublets
in motor cilia and flagella, outer doublets are connected to the central pair by ()
radial spokes
in motor cilia and flagella, outer doublets are connected to each other by links of a protein called ()
nexin
what proteins/structures are present in motor cilia/flagella but not in primary cilia?
- central pair of microtubules
- radial spokes
- nexin
- dyneins
in motor cilia and flagella, () → motor activity drives movement of cilia/flagella
dynein bases are attached at each A tubule; head groups attach to the B tubule of the adjacent microtubule doublet
how do motor cilia/flagella bend?
- dynein motor heads move along B tubules (towards minus ends) → A tubule of one doublet slides towards the base of the adjacent B tubule
- because the doublets are linked and held in place by nexin, the doublets bend
during mitosis, dynamic instability accelerates as a result of ()
increased microtubule growth and catastrophe rates
microtubule array in interphase cells disassembles to form the () (responsible for separation of daughter chromosomes)
mitotic spindle
restructuring of microtubule cytoskeleton is directed by duplication of (1) → forms 2 separate (2)
- centrosome
- microtubule organizing centers at opposite poles
what are the 3 kinds of microtubules involved in the formation of the mitotic spindle
- kinetochore microtubules
- interpolar microtubules
- astral microtubules
microtubules that attach to the condensed chromosomes of mitotic cells at their centromeres
kinetochore microtubules
microtubules that aren’t associated with chromosomes but are stabilized by overlapping with each other in the center of the cell
interpolar microtubules
microtubules that extend outward from the centrosomes to the cell periphery; plus ends are anchored in cell cortex
astral microtubules
how are duplicated chromosomes aligned at the metaphase plate
alignment of chromosomes is mediated by rapid growth of kinetochore microtubules and capture of their plus ends by kinetochores
what happens during Anaphase A
- chromosomes move towards the spindle poles along the kinetochore microtubules
- kinetochore microtubules shorten as they are disassembled by kinesins (act as microtubule-depolymerizing enzymes)
what happens in Anaphase B
- both interpolar and astral microtubules contribute to chromosome movement by pushing the spindle poles apart
- kinesins cross-linking interpolar microtubules move towards plus ends → causes overlap between interpolar microtubules to decrease and spindle pole to be pushed apart
- dyneins anchored on the cell cortex pull the spindle poles apart by pulling them closer to the cell cortex; this is aided by the depolymerization of astral microtubules as the dyneins move towards their minus end
