Slides 3: Cell motility, Cell contraction

Actin filaments

______ _________ regulate cell shape

stiff, elastic

Simpler in structure than microtubules but similar in their dynamic stability, actin filaments can be __ or __ depending on which other proteins they interact with

microvilli

Actin filaments serve many functions in the cells:

• Support for intestinal cell ____

muscle, myofibroblasts

Actin filaments serve many functions in the cells:

• Contraction in ____ cells and _____

filopodia, extensions

Actin filaments serve many functions in the cells:

• Generation, dynamics and support of ___ and other cell ____

contractile ring

Actin filaments serve many functions in the cells:

• __ during cell division

stiff, bundles

Actin filaments serve many functions in the cells:

• Support for intestinal cell microvilli: ___ actin __

flexible

Actin filaments serve many functions in the cells:

• Contraction in muscle cells and myofibroblasts: ___ actin

flexible, dynamic

Actin filaments serve many functions in the cells:

• Generation, dynamics and support of filopodia and other cell extensions: ___ and highly ___ actin

flexible, temporary

Actin filaments serve many functions in the cells:

• Contractile ring during cell division: __ and __ actin

ATP

Actin Structure and Assembly

• Actin filaments polymerize in a similar manner to microtubules except that ___ hydrolysis is associated with actin polymerization and depolymerization instead of GTP hydrolysis

subunit, plus, minus

Actin Structure and Assembly

• Actin dimers (___)

• add to the __ end

• leave from the __ end

ATP, ADP

Actin Structure and Assembly

• actin with bound ___ adds to plus end through ATP hydrolysis

• Actin with bound ___ leaves the minus end

actin treadmilling

Actin Structure and Assembly

• _______ _______ is the continuous addition at one end and dissociation from the other end of the G-actin monomers

  • is crucial to several functions in eukaryotic cells, such as cell migration, endocytosis, and exocytosis.

cortical actin, myosin-mediated

Cycles of ___ _____ polymerization and _____-_____ contraction allow cell movement and migration “forward”

actin polymerization, anchorage, contraction

Cycle of cortical actin polymerization/myosin-mediated contraction

• 1) ______ _____ at the leading edge of the cell pushes the plasma membrane forward (protrusion) and forms new regions of actin cortex

• 2) New points of ____ are made between the bottom of the cell and the surface on which the cell is crawling

• 3) _____ at the rear of the cell — mediated by myosin motor proteins moving along actin filaments — then draws the body of the cell forward

• 4) the same cycle is repeated over and over again, moving the cell forward in a stepwise fashion

lamellipodium, integrins, myosin, actin, protrusion

Cell movement

• 1) Actin polymerization at the plus end protrudes _________, movement of unpolymerized actin the the actin cortex is towards the lamellipodium

• 2) Attachment of protruded lamellipodium to the substratum through focal contacts (contain ___)

• 3) Contraction at the end of the cell opposite the lamellipodium by ____ motor proteins sliding along ___ filaments in the actin cortex

• 4) Further ____ of lamellipodium

• 5) Repeat

lamellipodium

____ is a cytoskeletal protein actin projection on the leading edge of the cell

substratum

____: an underlying layer or substance, in particular a layer of rock or soil beneath the surface of the ground

actin cortex

The ___ ___ is typically defined as a thin layer of actin meshwork that uniformly underlies the plasma membrane of the entire cell

Actin-related proteins, minus

__-__ __ (ARPs)

• associate with actin filaments and coordinate formation of the cortical actin networks that drives lamellipodium formation and advancement

• bind the __ end of actin

Myosin-I

Myosins are motor proteins

• also actin filaments can be used for vesicle transport or other movements mediated by _____-_

globular head, tail

Myosins are motor proteins

• The _______ _____ of Myosin-I attaches to an actin filament while the ___ that attaches to another molecule or organelle in the cell

cell cortex

Myosins are motor proteins

• Myosin-I can also bind to an actin filament in the ____ __, ultimately pulling the plasma membrane into a new shape

toward

Myosins are motor proteins

• Note that the head group always walks ___ the plue end of the actin filament

myosin-II

Muscle-specific myosins have evolved special structural organization

• a molecule of ____-_ contains two identical heavy chains, each with a globular head and an extended tail

coiled-coil

Muscle-specific myosins have evolved special structural organization

• the tails of the two heavy chains of myosin-II form a single __-__ tail

bipolar myosin filament

Muscle-specific myosins have evolved special structural organization

• the coiled-coil tails of myosin-II molecules associate with one another to form a ______ __________ ________ in which the heads project outward from the middle in opposite directions

tails

Muscle-specific myosins have evolved special structural organization

• the bare region in the middle of the bipolar myosin filament consists of __ only

sarcomere

Anatomical structure of muscle cells and the contractile unit: the ___

actin, myosin-II

Sarcomere

• thin filament (___)

• thick filament (__-__)

Z disc

sarcomere

• the __ __ anchors the actin-rich thin filaments and plays a crucial role in maintaining the mechanical stability of the cardiac muscle.

ATP, detaches, ATP, lever arm, phosphate, attaches, lever arm, ADP

Muscle contraction

• ___ binds myosin head

• myosin ___ from actin

• ___ hydrolysis

• ADP with P on myosin head, __ __ moves forward, moving myosin head up one actin monomer

• ___ leaves

• myosin head ____ to actin, but one actin monomer forward from start

• __ __ move back

• ___ leaves