Actin Filaments and Myosin

actin filament

thin type of protein filament composed of actin proteins

what does actin require to be assembled?

ATP

F-actin

fibrous protein made of a long chain of G-actin molecules twisted into a helix

G-actin

a globular subunit of F-actin with an active site for binding a myosin head

subunits of actin can be incorporated/released at either end, but which end tends to be added to?

plus end

actin binding protein

protein that interacts with actin monomers/filaments to control the assembly, structure, and behavior of actin filaments and networks

cortex of cell

network of microfilaments that form a semisolid support for the cell's shape

where are actin binding proteins commonly found?

in the cell cortex

monomer sequestering protein

protein that binds to free actin monomers and alters the G- to F-actin equilibrium

capping protein

protein that attaches to and stabilizes microtubules and prevents disassembly

monomer polymerizing protein

protein that promotes growth of actin filaments

membrane binding protein

protein that connects the cytoskeleton to the cell surface

what do cross-linking and bundling proteins do?

link actin filaments together to create strong structures

steps of cell migration

1. polarization

2. protrusion

3. adhesion

4. translocation

lamellipodium

sheetlike extension, rich in actin filaments, on the leading edge of a motile cell

where does actin polymerization occur in a migrating cell?

occurs at the plus end

where does unpolymerized actin go during cell migration?

moves towards the lamellipodium

an epithelial cell has __________ polarity

(constant/changing)

constant polarity

what determines the leading and lagging edge of a motile cell?

cell signaling reacts to the environment, which polarizes the cell

a motile cell has __________ polarity

(constant/changing)

changing polarity

how is the lamellipodium pushed forward?

a pool of actin monomers in the cytoplasm react to cell signaling, then the actin outgrowth pushes the membrane forward/out along the cell's leading edge

myosin

motor protein present in muscle fibers that aids in contraction

conventional myosin (type II)

motor protein; head domain binds to actin and it hydrolyzes ATP to move in its power stroke

unconventional myosin

motor protein that walks along an actin filament carrying cargo

actinmyosin

contracted form of actin and myosin

where do the myosin heads bind during contraction?

bind to actin

draw and label the following:

• a bundle of myosins

label A: myosin globular head and alpha-helical neck

label B: myosin tail domain

name the parts of myosin