Microtubules, Actin (and intermediate filaments). Macrophage microtubulin green Intermediate filaments red DNA blue. Mitochondria, actin. Cytoplasmic microtubules Cytoplasmic m tubules brkdwn Mitotic spindle Differentiated cell types have stable m tubule structures
(and intermediate filaments)
Macrophage microtubulin green
Intermediate filaments red
Differentiated cell types have
stable mtubule structures
Cilia, flagella form from
… hollow, rigid tubes composed of a/b heterodimers
POLAR.. w/o polarity, it can not function.
… but the beta
subunit has intrinsic
Assembly is initiated at MTOCs
MicroTubule Organizing Centers
100’s of g subunits serve to nucleate
Anti a tubulin, anti g tubulin
is related to the amt.
of free tubulin (Cc)
Growth when balanced
tipped toward >[Cc]
Occurs preferentially at the plus ends
Critical Concentration, Cc, above grows/below shrinks
Does not require GTP hydrolysis for assembly
The rapid nature of disassembly is due to its constrained
internal structure (GDP tubulin)
Colchicine (from crocus) binds free tubulin
Taxol (from yew) stabilizes microtubules
Both cancer therapy drugs, both block mitosis.
How? If opposite modes of action?
Image by Steve Rogers, UNC Dept. Biology. (Confocal Microscope)
Organelles, vesicles with culture.
cargo move around the cell.
How do we know? culture.
Pulse-chase with radioactive amino acids injected into rat ganglion
Assay, slice up axon over time, SDS PAGE autoradiography
but this is dramatically faster than diffusion in the axon.
…in a differentiated cell- dynamic instability is suppressed… by capping proteins.
increases resolution and
This movement requires ATP.
But AMP-PNP (analog)
… and AMP-PNP
Michael Sheetz, Columbia
Movie from Jeff Gelles lab
single kinesin molecule
means by which the cytoskeleton is used for trafficking.
It is important for cell shape, location and contraction
5% of total protein,
half as filaments
in 4 colors
ATP hydrolysis is not required for assembly.
Cytochalasins and lantrunculin
bind G actin
Nets and bundles.
These can be activated by recptors and in turn activate actin assembly
Actin-based movement of vesicles
Myosin-driven cell shape changes
Myosin I and myosin I
One head (ATPase) and one tail, tail varies Ras members
Dimer Ras members
300 heads here, bind actin
Multinucleate (formed by cell fusions
50 mm diameter and centimeters long)
… just one sarcomere Ras members .
Plus ends Ras members
Each filament has ~300 heads. Ras members
Each head binds 5X/s
32 mm in 0.1 s
Attached, No ATP, “rigor”
Released, binds ATP
Power stroke, loose ADP
T-tubules bring PM up close to the SR … Ras members