Contractile Proteins Flashcards
Give some examples of structures that utilize actin?
Microvilli, filopodia, contractile ring of cytokinesis
Accesorry proteins assemble actin filaments into actin bundles and actin networks, what are the differences?
Actin bundles are cross-linked into closely packed parallel arrays
Actin networks are loosely cross-linked in orthogonal arrays that form a meshwork and are flexible
How is cross-linking acheived?
by peptides and polypeptides have at least two actin-binding sites
How are the size and shape determined for the filaments?
the crosslinking proteins determine how close/far they will be from eachother EX: contractile are further away for myosin, parallel bundles are closer together because dont have myosin
Fimbrin binds to actin filaments as a monomer and holds two parallel filaments close together… what is an example of this?
Microvilli which increase cell absorption
Alpha-actinin binds to actin filaments as a dimer, which is a larger protein so there is more space between each actin filament called contractile bundles, what does this allow room for?
allows for motor protein (myosin) to interact during contraction, loosely bundled due to size of alpha actinin protein
Filamin is a large actin binding protein which binds as a dimer, creating a 3D network, crossing actin filaments. Where are the actin binding domains located?
They are located on the opposite ends of the dimer (dimerization domain)
What are abundant beneath the plasma membrane and what do they do? Example?
3D networks are abudant and they determine the shape of the cell, aid in movement, stability and flexibility of the membrane.
EX: spectrin in erythrocytes
What occurs when there is a mutation in the cytoskeleton proteins in erythrocytes (spectrin/ankyrin/4.1)?
Hereditary spherocytosis, decrease RBC, jaundice, become very round
What are pseudopodias?
based on actin filaments cross-linked into a 3D network responsible for phagocytosis
What are lamellipodia?
sheet like extensions on the edge of the cell, containing a network of actin filaments
What are filopodia?
thing projections of the plasma membrane supported by actin bundles, based on assembly (+ towards outside) and disassembly (- towards inside) of actin filaments
How does myosin move along actin?
What is the most common in skeletal muscle?
What are the three domains of myosin?
- move along via ATP hydrolysis
- Myosin II is most common
- Head neck and tail
What does the head domain of myosin consist of?
Actin binding and ATP binding sites, ATPase activity
What does the neck domain of myosin consist of?
Flexible region, binds myosin light chain peptides (common see more proteins here)
What does the tail domain of myosin consist of?
intertwined to bring myosin regions in close proximity, bind membrane/organelles
What are the steps for how myosin moves along F-actin? (4)
- ATP binds myosin, causing a conformational change and releases head from actin
- Hydrolysis of ATP to ADP + Pi, Myosin in cocked state until binding to actin
- Binds actin releases Pi (energy) to drive power stroke
(conformational change in neck, moves actin filament) - ATP binds to myosin, releasing ADP, head released from actin
The amount of velocity and powerstoke of the myosin depends on what?
If there is a longer neck domain on the myosin, the velocity and quickness of the reaction will be increased.(ex: myosin V will have faster velocity than myosin II due to longer neck)
In the sarcromere, there is a positive end at the Z disk and negative charge at the M band/ end of the actin, which way does myosin move towards?
Move towards the positive charge on z disk to contract the muscle
For smooth muscle, how is folded myosin activated to contract with actin, making the cell become globular?
When there is an increase in Calcium due to an extracellular signal, the myosin light chain becomes phosphorylated, unfolded, and active
What is an example of a non-muscle cell contraction, and how does it occur?
An example is cytokinesis, bundles of f-actin and myosin II form the contractile ring, which contracts creating a cleavage furrow
How is vesicular transport done regarding actin-myosin?
Myosin V moves towards positive end of actin, myosin VI moves towards minus end of actin, activated when cargo is present, attached by tail
How is cell migration done by actin-myosin contractions?
Actin and myosin contractile bundles pull focal adhesions off the plasma membrane, allowing it to migrate.
Actin stess fibers are in middle and actin is plentiful at the leading edge of a cell
What is duchene muscular dystrophy (DMD)?
X-linked recessive disorder, muscle wasting, wheel chair by 12 y/o, due to mutations in dystrophin gene
What mutation is worse, in frame or out of frame mutations?
out of frame (DMD) in frame will still have partial activity of gene, called Becker muscular dystrophy
What does dystrophin do in muscle contractions?
Relieves stress of the contraction and releases the energy laterally and longitudinally, without will see bursting/rupture of muscle cell and cell death, scar tissue grows.
