Actin Filaments Flashcards
Functions?
Cell movement especially those involving cell surface.
Maintain cell shape
Muscle contraction
Cell motility in pseudopodia
Cell division
Cytoplasmic streaming
Is it unstable?
Yes
When is it stable
When associating with other proteins
Microvilli??
Found on epithelial cells lining the intestine
Small contractile bundles?
Contract and act as ting muscles in animal cells
They can also for temporary structures such as..
Dynamic protrusions formed at the leading edge of a crawling cell
Lastly they can form..
Contractile ring
Do they require association with a motor protein for movement?
Yes
What is that motor protein called?
Myosin
Just like microtubule they can..
Assemble and disassemble.
If actin concentration is high..
Monomers are added to both ends
What is treadmilling
Treadmilling is a process that is seen in actin filaments and microtubules, among other cellular cytoskeletal filaments. A segment of the filament seems to “move” through a stratum or the cytosol when one end of the filament lengthens while the other end shortens.
In human rbc a simple and regular network of fibrous protein including… …. Attach to cell membrane send provide support necessary for the cells to maintain their simple shape
Spectrin and actin
Cell crawling depends on cortical actin
True
How does a cell crawl?
1.the cell pushes out protrusions at its “front,” or leading edge; 2.these protrusions adhere to the surface over which the cell is crawling; and 3.the rest of the cell drags itself forward by traction on these anchorage points.
Actin polymerization at the leading edge of the cell pushes the plasma membrane forward and forms new regions of
Actin cortex
The cell forms new attachments to the surface it’s moving on
True
At the rear myosin motor
Contract and pulls cell forward
web undergoes continual assembly at the leading edge and disassembly further back,
pushing the lamellipodium forward.
Myosin 1 is present in all cells types
True
Structure of myosin I
Head domain and a tail
How to move a vesicle relative to an actin filament that is anchored to cell membrane
The head domain binds to an actin filament and has the ATP-hydrolyzing motor activity that enables it to move along the filament in a repetitive cycle of binding, detachment, and rebinding
Myosin can pull plasma membrane into a new shape
True
Muscle myosin belongs to
Myosin 2
Myosin 2 structure
Two head and one tail
One set binds..
to actin filaments in one orientation and moves the filaments one way; the other set binds to other actin filaments in the opposite orientation and moves the filaments in the opposite direction
As a result
myosin filament slides sets of oppositely oriented actin filaments past one another.
Skeletal muscles are huge
True
Structure
multinucleated individual cells formed by the fusion of many separate smaller cells
The nuclei of the contributing cells are retained in the muscle fiber and..
lie just beneath the plasma membrane
A myofibril consists of
a chain of identical tiny contractile units, or sarcomeres
What gives a myofibril a stripped pattern
and the repeating pattern of sarcomeres.
Sarcomeres consist of
actin filaments and myosin filaments composed of a muscle specific form of myosin-II.
The myosin filaments (the thick filaments) are … positioned in each sarcomere, whereas the more slender actin filaments (the thin filaments) of the sarcomere, where they are anchored by their plus ends to a structure known as the …
Centrally
extend inward from each end
Z disc
The contraction of a muscle cell is caused by ..
simultaneous shortening of all the cell’s sarcomeres,
How does shortening occur
which is caused by the actin filaments sliding past the myosin filaments, with no change in the length of either type of filament
When a muscle is stimulated to contract
the myosin heads start to walk along the actin filament in repeated cycles of attachment and detachment.
When does it happen
only when the skeletal muscle receives a signal from a motor nerve.
The electrical signal is then relayed to the
Sacroplasmic reticulum
response to the incoming electrical excitation
much of this Ca2+ is released into the cytosol through a specialized set of ion channels that open in the sarcoplasmic reticulum membrane in response to the change in voltage across the plasma membrane and T tubules.
Skeletal muscle contraction is triggered by the release of Ca2+ from the sarcoplasmic reticulum into the cytosol.
True
the rise in cytosolic Ca2+ concentration activates a molecular switch made of specialized accessory proteins closely associated with the actin filaments
molecular switch made of specialized accessory proteins closely associated with the actin filaments called tropomyosin
What does tropomyosin do
where it prevents the myosin heads from associating with the actin filament.
When the concentration of Ca2+ rises in the cytosol, Ca2+ binds to troponin and induces a change in the shape of the troponin complex. This in turn causes the tropomyosin molecules to shift their positions slightly, allowing myosin heads to bind to the actin filaments, initiating contraction
True
As soon as the Ca2+ concentration returns to the resting level,
troponin and tropomyosin molecules move back to their original positions. This reconfiguration once again blocks myosin binding to actin filaments, thereby ending the contraction.
smooth muscle, which is present in the walls of the stomach, intestine, uterus, and arteries, and in many other structures
undergo slow and sustained involuntary contractions.
Why is This mode of myosin activation is relatively slow
because time is needed for enzyme molecules to diffuse to the myosin heads and carry out the phosphorylation and subsequent dephosphorylation.
Why does this mechanism has the advantage
unlike the mechanism used by skeletal muscle cells—it can be activated by a variety of extracellular signals: thus smooth muscle, for example, is triggered to contract by adrenaline, serotonin, prostaglandins, and several other signal molecules.
