Quiz 2 Flashcards
What type of pathway is the Delta/Notch Signaling Pathway?
Contact-dependent signaling
Cell with Delta proteins become…
Neuron cells
Cell with Notch become…
Epithelial cell (not neuron)
What happens in the absence of Wnt?
Beta-catenin is sequestered in a degradation complex, and gets broken down
Is Frizzled a GPCR?
NO! There is no G-protein associated with
What happens in the Hedgehog pathway when Hedgehog is absent? (3)
-Patched keeps Smoothened inactive and sequestered in intracellular vesicles in the cytosol
-The Ci protein is proteolytically processed
-The cleaved tail of the Ci protein translocates to the nucleus and acts as a transcription repressor
Three major families of cytoskeleton components
Intermediate Filaments, Microtubules, Actin filaments
Actin filaments
Comprised of actin subunits and are polar
Determine shape of cell’s surface
Necessary for the whole-cell locomotion
Drives pinching of one cell into two
Describe actin subunits
Monomeric, globular proteins with ATP-binding domain (ATP can be hydrolyzed)
What does it mean for a molecule to be polar
They have a plus end and a minus end.
Describe the plus end of actin?
Barbed and polymerize quickly
Describe the minus end
Pointed and polyermize slowly
Nucleation
When two actin molecules bind relatively weakly, but the addition of a third monomer forms a trimer that is much more stable
What are the three phases to the time course of polymerization?
Lag phase, Growth phase, Equilibrium/steady state
What is the Lag phase of polymerization?
Time taken for nucleation
What is the Growth phase of polymerization?
Occurs as monomers are adding to the exposed ends of the growing filament, causing filament elongation
What is the Equilibrium/steady state of polymerization?
Reached when the growth of the polymer balances the shrinkage of polymer
How can you abolish the Lag phase?
Adding premade nuclei (seed filaments)
What is treadmilling?
When polymerization of the + end is the same rate as depolarization of the - end
What does Thymosin do?
Prevent polymerization by holding the monomers like a dragon with its treasure
What does Profilin do?
Promote polymerization by taking subunits and add them to polymer.
What does ARP 2/3 complex do?
Creates structures of branching actin filaments; nucleates filaments at the minus end (cap -)
What does Formins do?
Creates parallel bundles of actin filaments (dimmer reaches out and grabs subunits)
What do Side-binding proteins do?
Stabilize and modulate interactions with other proteins (Tropomyosin)
What do Cap-binding proteins do?
Stabilize + or - end
What Cap-binding protein binds the - end?
ARP 2/3 complex
What Cap-binding protein binds the + end?
Cap Z
What does Tropomodulin do?
Bind the - end of tropomyosin-coated filaments as a capping protein
What do Accessory proteins do?
Promote nucleation OR promote rapid depolymerization
What are the 2 classes of Accessory proteins?
Gelsolin Superfamily and Cofilin
What do the Gelsolin family of proteins do?
Interact with sides of filaments and cuts them
What do Cofilin proteins do?
Preferentially binds along ADP bound length of actin, then twists and weakens the filament
What is fimbrin?
Protein that binds with actin filaments to make parallel bundles
What are parallele bundles?
Tight packing bundles that prevent myosin II from entering the bundle and binding
What does alpha- actin in do?
Bind with actin filaments to form contractile bundles
What are contractile bundles?
Loose packing actin bundles that allow myosin II to enter the bundle and bind
What to filamin dimers do?
Allow for 3D mesh/gel to form
What does myosin consist of?
2 heavy chains and 2 light chains
Which myosin chain has globular domains?
Heavy
What creates the myosin tail?
Long AA chain
CAn Myosin move if ATP is bound?
NO
Steps of myosin movement (4)
Attached-Myosin head is tightly attached to actin
Released- ATP binds to large cleft on the back of the myosin head. Myosin releases from actin
Cocked- Cleft on the back of the myosin closes around ATP mol. Triggers movement in lever arm, displacing the myosin head. ATP is hydrolyzed. ADP and Pi remain tightly bound
Force-Generating- Myosin head weakly binds to new sire on actin. Pi is released and myosin-actin bond is tightened. Power stroke occurs, moving actin filament and releasing ADP
BACK TO ATTACHED
Myofibril
cylindrical structures, long chain of tiny contractile units
Sarcomeres
Contractile
How do muscles contract (6)
- Depolarization of the plasma membrane causes voltage gated Ca2+ channels to open in T-tubules
- Sacroplasmic reticulum Ca2+ channels also open
- Ca2+ flows into cytosol from T-tubules and the SR
- Ca2+ binds to troponin complex
- Tropomyosin moves
- Allows myosin to bind to actin filaments
