Lecture 14- cytoskeleton, actin, cell motility, muscle

Kartagener Syndrome
• cilia have defective or no what

movement

what motors associate with Actin filaments

Myosin

head domain binds what and hydrolyzes ATP to move in power stroke

actin

actin filaments= F-actin

microfilaments

what polymers of actin protein monomers (G-actin)

polarized

microfilaments assembly requires what

ATP

F-actin dynamics
• elongation is much faster than nucleation (like MTs) – need what to start

nucleus

subunits incorporated/released tend to be
what to the plus end, what from the minus end

added, released

the plus end has a what affinity for ATP-actin than the
minus end does

higher

at LOW ATP-actin concentrations, growth at what end

plus

nucleation is energetically what- must have nucleating proteins, ie, the Arp2/3 complex or Formins, also (Listeria) ActA

unfavored

Actin binding proteins can promote filament what

formation

cell biologists often use fluorescently labeled phalloidin to see the actin’s what

cortex

blocks plus ends

cytochalasin D

binds filaments and prevents breakdown

phalloidin

binds/sequesters free monomers

latrunculin

cytochalasin treated cells –predictions

what aspect of actin dynamics helps
to explain this result?

treadmilling of subunit addition/release

Actin binding proteins can what filament formation

decrease

monomer sequestering proteins alter what- to what-Actin equilibrium

G to F

Actin binding proteins can stabilize what or link them

filaments

monomer polymerizing proteins promote growth

Profilin

capping proteins can stabilize what of a filament

length

membrane-binding proteins connect the what to the cell surface

cytoskeleton

Actin filaments are linked into into what structures

3D

cross-linking and bundling proteins create what structures
(microvilli, stereocilia)

strong

filament-severing what can break filaments into smaller
filaments

proteins

Listeria capitalizes on host what

Actin

a migrating cell polarizes in response to the what

environment

the Rho family of monomeric GTPases promote what reorganization

actin

in an experiment, you bind myosin S1 fragments to a coverslip and add stabilized, labeled Actin filaments and ATP. what happens?

the actin binds but doesn’t move

unconventional myosins walk on actin filaments and can carry what

cargo

myosins I, V, and VI are associated with what vesicles
and organelles

cytoplasmic

smallest contractile unit

sarcomere

skeletal muscle and cardiac muscle cells are comprised of what

myofibrils

myosin II forms what that pull on actin filaments

filaments

Thick filaments

myosin

Thin filaments

actin

Thick (myosin) and Thin (Actin) Filaments Do or Do Not change their length- only the extent of overlap changes as sarcomere contracts/extends

Do Not

Tropomyosin molecule associates with # Actin subunits

7

Tropomyosin’s location along the Actin filament is what dependent

Ca2+

Troponin does what filament by association with Actin and Tropomyosin

stabilizes

the largest protein known – 38000 amino acids

Titin

may prevent overstretching; positions myosins

Titin

Nebulin may determine the size of the what

sarcomere

what binds ATP and releases F-Actin

Myosin

if you stretched a relaxed myofibril, which bands/zones would NOT change in size?

A band

in a stretched myofibril where sarcomeres are 50% longer, do you expect the contractile strength to be

reduced

for someone who was immobilized by the curse Petrificus Totalus, in which all the skeletal muscles stiffen, in which state would you expect most of the victim’s muscle myosin?

not bound to either ADP or ATP

motor neurons do what to a muscle at the neuromuscular junction

signal

impulse causes the sarcoplasmic reticulum to do what Ca2

release

high Ca2+ relocalizes Tropomyosin and allows what to bind Actin

Myosin

muscle contraction triggered by Ca++ release into what

cytosol