Cytoskeleton Flashcards
monomers of actin are ___-actin and polymerized actin is __-actin
G-actin = monomer
F-actin = polymerized actin (filaments = F)
match for an actin molecule:
barbed and pointed end
minus end and plus end
barbed end = + end
pointed end = - end
actin filaments have polarity
rate limiting step of actin polymerization
nucleation
3 actin molecules have to come together to form a nucleus first, then polymerization process can occur (elongation, treadmilling)
in actin polymerization, elongation occurs at ___ end
elongation of ATP-actin preferentially at barbed (+) end
at same time, ATP hydrolysis is occurring on (-) end where polymerization speed is slower —> steady state is achieved (ADP-actin is unstable, depolymerizes from minus, pointed end) —> treadmilling
actin polymerization treadmilling
filament grows on (+)/barbed end and simultaneously dissociates from (-)/pointed end
length of actin isn’t really changing but it is moving forward
[ remember: (+) end is the leading end —> moving in (+) direction]
this small G protein is very important for regulation of actin dynamics
Rho GTPase
defects in Rho GTPase can cause defect in actin polymerization —> associated with intellectual disability
how do each of these toxins target the actin cytoskeleton:
a. phalloidin
b. cytochalasin
c. latrunculin
a. phalloidin: binds and stabilizes actin filaments (found in death angel mushrooms)
b. cytochalasin: binds (+) end and blocks polymerization (produced by molds)
c. latrunculin: binds actin monomers and prevents polymerization (produced by sponges)
how do Listeria and Rickettsia (rocky mountain fever) bacteria target actin
hijack host actin polymerization machinery for cell to cell spreading
actin “tricked” into polymerizing at tail of bacteria, and bacteria use that force to enter other cells
can spread without detection
subunits of microtubules and features
dimer of alpha and beta tubulin, arranged in tubules with 13 protofilaments
thickest cytoskeleton structure
motor proteins: kinesin and dynein
has polarity
function: intracelular transport, cell division, cell motility
binds GDP/GTP
what cytoskeleton structure forms mitotic spindles and cilia/flagella?
microtubules: important for mitosis
Mitosis = Microtubules
centrosome is the _____ organizing center
microtubule - radiate outwards from centrosome, which stabilizes minus end
dynamic instability of microtubules
intrinsic property of microtubules
- catastrophe: GTP hydrolysis occurring at same time as polymerization, which eventually catches up to tip of plus end, loss of GTP cap
- rescue: rapid shrinking/depolymerization
- growing resumes until catastrophe occurs again (cycle)
both growing and shrinking is happening at (+) end, minus end is stabilized by centrosome
how do each of these natural toxins target microtubules:
a. paclitaxel
b. colchicine
c. vincristine
a. paclitaxel: binds and stabilizes microtubules
b. colchicine: binds tubulin and blocks polymerization
c. vincristine: binds tubulin and blocks polymerization
dysfunction of this cytoskeleton structure contributes to development of Alzheimer’s
microtubules
intracelular neurofibrillary tangles interfere (hyper-phosphorylated tau)
what are the three cytoskeleton motor proteins and which direction do they move
myosin (actin associated): moves towards + end
kinesin (tubulin associated): moves towards + end
dynein (tubulin associated): moves towards - end
which is associated with long-range transport: actin or microtubules
microtubules: it’s larger (think of highway vs local road)
actin: local transport
structure of myosin
actin motor, large gene family
2 heavy chains and 2+ light chains
plus-end directed
globular head or motor domain with ATPase,
tail domain is variable - contains coiled coil for dimerization and/or binds cargo
what two things are required for movement of myosin along actin filament
mechanical cycle (changes in confirmation, attachment and unattachment) and chemical cycle (ATP hydrolysis)
what cytoskeleton component is important for cytokinesis
actin and myosin II create contractile ring that cleaves the cell
congenital heart disease and cardiomyopathy is associated with defective:
a. actin
b. microtubules
c. intermediate filaments
actin - heavily expressed in the heart muscles (for contraction)
Griscelli syndrome Type 1 presentation and cause
silver hair, light skin, severe neurological effects
mutation in myosin Va, which is required for distribution of melanosomes to cell periphery
[can also be caused by mutation in melanophilin or Rab27a]
pt. is 2yo M that presents with silvery hair, light skin, and severe neurological defects. A mutation is found that affects cytoskeleton function. What is your diagnosis and what is the mutation affecting
Griscelli syndrome Type 1
mutation affecting myosin - melanosomes are not able to be distributed to cell periphery
what is the basic structure of kinesin, and how does it “walk”
head domain with ATPase
tail region that binds target or light chains or dimerizes
walking:
1. forward motor binds beta-tubulin, releasing ADP and binding ATP
2. conformational change causes rear head to swing forward (“walking like a drunk”)
3. new head releases ADP to bind ATP, trailing head hydrolyzes ATP
4. cycle continues
basic structure of dynein
microtubule motor that is minus-end directed
head with ATPase activity
microtubule-binding domain in the stalk
stem/tail binds light chain or cargo or another microtubule
Kartagener Syndrome
aka Primary Ciliary Dsykinesia
caused by mutations in axonemal dynein heavy chain (axonemal dynein important for cilia and flagella)
effect: cilia are immobile, chronic infection of respiratory tract (can’t clear infection), sterile males (sperm are immobile without functional flagella)
A patient in your clinic presents with chronic infections of the respiratory tract. They say they have a hard time clearing mucous. Genetic testing shows their cilia are immobile, and the patient (M) is sterile. What is your diagnosis?
Kartagener syndrome, aka Primary Ciliary Dyskinesia
mutation in axonemal dynein heavy chain important for cilia and flagella beating
long range axonal transport in neurons depends on _____
microtubules
what are the characteristics of intermediate filaments
no polarity, no motors
maintain cell shape and mechanical strength (“tendons” of the cell)
assemble as antiparallel tetramers
strongest type of cytoskeletal structure - “tendons” of the cell
intermediate filaments
keratins and lamins belong to what class of cytoskeleton
intermediate filaments
neurofilaments (type of intermediate filament) travel along ____
axonal microtubules
so problems with axonal microtubule could cause secondary problems with intermediate filaments
variable ___ domains of kinesins allow binding to specific [forms of microtubules OR cargos and targets]
variable TAIL domains bind specific CARGOS and TARGETS
motor domain is highly conserved
