Lecture 17: Contractile Protiens Flashcards
Actin
What does this cytoskeletal protein determine?
- Shape of the Cell
- Cell Locomotion
- Pinching of One Cell into two
- Mitosis
Myosin
What is this cytoskeletal protein functions?
- Use ATP to move organelles along filaments
- Use ATP to move filaments on proteins
On which end of actin do we typically see growth?
The plus end
In G Actin, where can you find ATP?
In the ATP cleft, which faces the minus end
How does actin assemble into a filament?
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Stage 1: Nucleation (Lag Phase)
- Small acting oligomers must first form an aggregate of 3 actin monomers
- Each aggregate must be stabilized
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Stage 2: Elongation (Growth Phase)
- Multiple subunits contract and elongate rapidly
- If actin is bound to ATP, polymerization happens much more quickly
-
Stage 3: Steady State (Equilibrium)
- Depends on concentration of free actin
- Rate of polymerization = Rate of depolymerization
What is the difference between the rate of subunit association and dissociation?
When is equilibrium reached between the two?
-
Subunit association: Proportional to concentration of free monomers
- C x kon
- Subunit dissociation: Independent of monomer concentration
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Equilibrium: Reached at critical concentration of monomers
- koff = Cc x kon
Where can you find actin filaments?
- Beneath plasma membrane
- Mechanical Support
- Determining Cell Shape
- Movement of Cell Surface
What determines the nature of the association of actin filaments?
How is cross linking achieved in F-actin?
The size and shape of the actin binding proteins
Acessory Proteins
What is the basic organization of actin parallel arrays?
What monomer binds the parralel arrays?
- Actin fibers are crosslinked together with all of their plus and minus ends on the same side.
- Parallel fibers are very close and doesn’t allow Myosin II from entering the bundle
- Fimbrin binds actin
Where in the cell can you find actin parallel bundles?
What do they do?
Location
- Projections of Plasma Membranes
- Microvilli
- Cell Cortex
- Adherens belt
Functions
- Placement of receptors and channels
- Facilitate signaling, transport, uptake of nutrients
Where do you see ATPase activity in Myosin?
In the Head region
What is a contractile ring made of?
Actin and Myosin II
What is the function of Myosin VI?
Moving vesicles towards the negative end of actin.
What actin bundling protein is present in contractile bundles?
Is this a tight or loose bundle?
Alpha-Actinin
Loose
Which end of actin does myosin move towards?
The plus end
What enzyme in smooth muscle activates myosin?
Myosin Light Chain Kinase
What actin bundling protein would you find cross linking the actin in a microvillus?
Why?
Fimbrin
Fimbrin holds actin fibers close together, which is more beneficial in a microvillus
What does the Dystrophen Gene do?
Connects Cytoskeleton to the basal lamina, stabilizes the membrane, and in so doing, helps to relieve the stress of contraction by spreading the forces out.
For Filamin:
Where are its actin binding domains located?
At the farthest ends of a dimerized structure
In a sarcomere, which side of the actin would be the plus side?
The side attached to the Z Disc
What is the function of Myosin I?
Assists with endocytosis
What causes a myosin “power stroke?”
Release of Pi
In a sarcomere which side of the actin would be the minus side?
The side farthest from the Z Disk (in the A Band)
Which myosin might you find associated with a membrane?
Myosin I
What do contractile bundles do to help a cell move forward?
They pull the plunger-like integrins off of the extracellular matrix so they don’t get stuck.
What is the function of Myosin V?
Organelle and Vescicle transport along the actin cytoskeleton.
What is filamin?
What is its function?
Actin binding protein
Creates three dimensional meshworks by binding to an actin binding domain on two different actin fibers.
What is the organizational name for actin networks’ three dimensional meshworks?
Orthogonal Arrays
What -podia are commonly associated with phagocytosis?
Pseudopodia
Erythrocytes contain spectrin:
What does it do?
Forms the actin network that makes up the cortical cytoskeleton
Where would we see an actin contractile bundle?
In muscles to assist in contraction
In the contractile ring of mitosis
What is the only myosin that moves towards the negative end of actin?
Myosin VI
Which myosin is typically associated with skeletal muscle?
Myosin II
What fiber is an essential component of pseudopodia, filopodia, and lamellopodia?
Actin
What is the heredity of Duchene’s Muscular Dystrophy?
X Linked Recessive
What will a myosin with a longer neck have over a myosin with a shorter neck?
A Myosin with a longer neck will have a greater power stroke velocity (increased rate of movement)
(Keep in mind this is not referring to the length of the tail, but the light chain neck portion)
What might be deficient in Hereditary Spherocytosis?
Cortical skeleton of the red blood cells
(More specifically, Spectrin, Ankryin, or Protein 4.1)
Where might you find myosin light chain peptides?
In the Neck region
What contributes to the prevention of myosin binding to actin in smooth muscle?
What enzyme causes this inhibitory state?
Folding of the myosin by the regulatory light chains in the neck
Myosin Light Chain Phosphatase
