L17: cytoskeleton & motility

Question 1

Microtubules

Answer 1

thick, strong
25 nm
subunit: ab-tubulin heterodimers

functions:
chromosome movements (miotic spindle)
maintaining shape & polarity
trafficking organelles (vesicles transported along the
microtubules)
cell motility

Question 2

microfilaments

Answer 2

8nm
subunit: g-actin monomers (twisted strands of beads)

functions:
muscle contraction
cell locomotion
cytoplasmic streaming

Question 3

intermediate filaments

Answer 3

8-12nm
subunit: IF dimer

functions:
shape maintenance
nuclear scaffolding (nucleus)
neurofilaments (hold axons)

Question 4

mircotubule structure:

Answer 4

arranged in spiral

how much strength is needed?
singlet: most cytoplasmic MT
doublet: in cilia and flagella
triplet: in basal bodies and centrioles

Question 5

microtubule assembly in vitro (order of assembly)

Answer 5

polar
tubulin dimers–> oligomers–> protofilament–> sheets of protofilament–> closing microtubules (sheath)–> elongating microtubule (+/-)

Question 6

microtubule treadmilling

Answer 6

when one end keeps adding/ one end keeps removing

microtubules eventually reach the end = and break away from the microtubules

Question 7

Microfilament structure

Answer 7

G-acton—atp—F-actin
2 strings of beads twisted around each other

leading-edge: front
trailing edge: back

Question 8

Microfilament: parallel bundle

Answer 8

towards the leading edge
one direction ==> (extend)

Question 9

microfilament: gel

Answer 9

flexible (can move in any direction)
mesh-like

Question 10

microfilament: contractile bile

Answer 10

at the end of trailing edge
antiparallel ==><===
maintain shape & create strength

Question 11

how does listeria invade cells

Answer 11

use actin filaments
-they internalized+divide
-form tail formation and move into the next cell without leaving the cytoplasm

Question 12

intermediate filament assembly

Answer 12

appearance: twisted polypeptide chains

dimer-> tetramer-> protofilaments-> intermediate filament