Cytoskeleton and Motor Proteins (Sayner) Flashcards
actin microfilaments
rigid, least deformable
can withstand some force then rupture
actin functions
beneath plasma membrane: give shape to lipid bilayer
muscle contraction
cytokinetic ring
cell surface projections: motility
actin monomers and polymers
G-actin monomers (globular) –> F-actin polymers (filamentous)
Synthesis of actin
G-actin + ATP –> hydrolysis, binds F-actin –> F-actin + ADP
F-actin is (polar/nonpolar)
Polar
Treadmilling
F-actin
minus end: slow growing, subunit disassembly
plus end: fast growing, subunit addition
actin inhibitors/toxins
cytochalasins
phalloidin
latrunculins
cytochalasins
cause depolymerization of F-actin
bind plus end –> prevent addition
cy+ochalasin binds the plus end
phalloidin
stabilize F-actin
bind to F-actin –> prevent depolymerization (impeding treadmilling)
latrunculins
cause depolymerization of F-actin
bind G-actin –> prevent reincorporation (during treadmilling)
Actin binding proteins (5)
profilin
thymosin
fimbrin
actin-related proteins (ARPs)
cofilin
Mnemonic: Proteins That Find Actin Cool
profilin competes with…
thymosin
profilin
binds G-actin at plus end –> allows minus end to polymerize
*promotes exchange of ADP for ATP –> accelerates assembly
ACIDIC membrane phospholipids promote
mnemonic: PROfilin PROmotes exchange
thymosin
binds G-actin and prevents incorporation into filaments
mnemonic: reach between the THYs (thighs) to find the G (-actin)
Fimbrin
cross links actin; forms tightly packed parallel bundles/arrays
Actin-related proteins
ARP2 and ARP3
favor polymerization
activated by Rac
acts as seed/stabilizing platform for actin and minus end
builds a tree like web
cofilin
mnemonic: coFilin binds F-actin
binds F-actin –> twists/applies mechanical stress –> breakage –> rapid disassembly
actin DEPOLYMERIZING factor
cofilin is inactivated/phosphorylated by…
Rho A
ARPs are activated by…
Rac
protrusion
occurs at leading edge
chemokines –> Rac activation –> activates ARP 2/3 (polymerization) –> lamellipodia extension
cofilin –> disassembly behind leading edge
attachment
integrins –> bind fibronectins –> link into actin cytoskeleton
contraction
occurs at trailing edge
Rho –> activates myosine contractile machinery
microtubules
train tracks
mitotic spindles
microtubule synthesis
polarity of microtubules
alpha: minus end
beta: plus end (faster addition)
mnemonic: beta +
T-form
microtubule stable form
beta + GTP → T-form → strong, lateral contacts
D-form
microtuble rapid depolymerization form
hydrolysis → beta + GDP → D-form → curve/rapid depolymerization
Microtubule orientation
negative (minus end): toward nucleus
positive (plus end): toward periphery
dynein
minus end directed
toward nucleus
kinesin
plus end directed
toward periphery
flagella arrangement
9 + 2 microtubule arrangement
outer and inner dynein arms
cilia are found:
in sperm tails and lining the:
respiratory tract
fallopian tubes
urinary tract
keratins
Types I and II intermediate filaments
anchor into cell membrane
Lamins
type v intermediate filament
found in inner nuclear membrane
function: nuceleoskeletal support/DNA protection
