Pset 1 Concepts Flashcards
Which motor protein mediates dispersion/aggregation and why?
Dynein mediates aggregation and kinesin mediates dispersion. Dynein, a minus end-directed motor, transports
[X] along microtubules towards the center of the cell, and kinesin, a plus end-directed motor, transports [X] along microtubules toward the cell periphery.
the organization of the microtubule cytoskeleton in interphase cells
Microtubules radiate from the
centrosome, with minus ends embedded in the centrosome near the nucleus and plus ends
extending towards the cell periphery.
One mechanism that cells employ to directly regulate protein function
Post-translational modifications (i.e. the addition of functional groups to protein side chains) is one of the most common mechanisms cells employ to directly regulate protein function. The most common post-translational modification is phosphorylation, in which a phosphate group is transferred from ATP to an amino acid side chain (serine, threonine, or tyrosine, all of which
contain hydroxyl groups). The phosphate group affects protein function either by inducing conformational changes and/or changing binding affinities. Protein kinases catalyze the addition of the phosphate group, and protein phosphatases catalyze its removal.
Hormone redistribution of given molecule vs. change in gene expression
Depending on the info given regarding redistribution (could be based on observation) but generally, Changes in gene expression take much longer (hours) than hormone-triggered redistribution of a molecule (potentially on time scale of minutes).
Western blotting
involves separating proteins by their size
using gel electrophoresis (specifically SDS-PAGE), transferring the separated proteins from the
gel to a nitrocellulose membrane (which looks like a thick piece of paper), and labelling a specific
protein by incubating the membrane with an antibody (e.g. anti-dynein IC1 or anti-kinesin LC1).
Two specific molecular mechanisms that could, in
principle, regulate motor-microtubule binding.
Hormone treatment could trigger post-translational modification (e.g. phosphorylation) of one of
the motors, which, in turn, could induce a conformational change that affects microtubule binding
affinity. Alternatively (or in addition), hormone treatment could up- or down-regulate a MAP or
MAPs that binds to microtubules and prevents kinesin or dynein from binding to the microtubule.
TIRF microscopy, and why do the authors use TIRF instead of regular epifluorescence
microscopy
TIRF (Total Internal Reflection Fluorescence) microscopy is a type of light microscopy in which
light from a laser beam, when it strikes a glass coverslip at a critical angle, is entirely reflected, generating a highly restricted electromagnetic field right at the surface of the coverslip. This evanescent field has a frequency identical to the incident light, and it decays exponentially with
distance from the surface of the coverslip. Because of this, the evanescent field excites
fluorophores only within ~200 nm of the surface. TIRF is useful for in vitro motility experiments,
because it allows for resolution of individual, fluorophore-tagged molecules (e.g. the chassis in
this paper) bound to the surface against a sea of unbound molecules floating in solution above the
surface.
Inertia in cell motor movement?
Molecules and cells operate at a
very low Reynolds number, where viscous forces dominate over inertial forces. Inertia plays no
role whatsoever!
