Contractile Proteins Flashcards
Define actin
A major component of the cytoskeleton
Organized by proteins into diverse structural groups
How are actin filaments assembled
Via accessory protein pathways
Actin is assembled into what two general types of structures
- Actin bundles
2. Actin networks
Define actin bundles
Cross-linkage of F-Actin which is achieved by peptide and polypeptides having at least two actin binding sites
The bundling proteins are small and rigid which force the filaments to align closely together
Actin bundles can be what or what
Tight or loose
What binds to actin filaments within tight actin bundles to hold them together
Fimbrin
Give an example of tight actin bundling
Microvilli
Define loose actin bundles
Aka contractile bundles
Uses alpha actin
Filaments separated by greater distances
Allows for motor proteins (myosin) to interact during contraction
Define network actin bundles
Actin filaments in a network that are held together by large actin binding proteins
Ex. Filamin
Actin binding domains are located on either end of dimer
Mutations in cortical cytoskeleton proteins in RBC is a mutation in what and can cause what
Mutation in spectrin and ankyrin
Can cause hereditary spherocytosis
S/S of hereditary spherocytosis
Flexibility and stability of RBCs are impaired
Decreased RBC’s (anemia)
Jaundice
Hepatosplenomegaly
Define pseudopodia
Actin projection based on actin filaments cross-linked into a 3D network that are responsible for phagocytosis
Define lamellipodia
Broad, sheet like extensions at the leading edge of cell, containing a networks of actin filaments
Define filopodia
Thin projections of the plasma membrane supported by actin bundles
Define myosin
A superfamily of motor proteins that move along actin filaments via ATP hydrolysis
Define Myosin Class 1
1 head with a light chain
Involved in membrane interactions
Define myosin Class 2
Aka skeletal muscle myosin
Bipolar filament with two heads
Used in skeletal muscle contraction
Define mysoin class 5
4 heads
Used in transport along cytoskeletal actin
What are the three domains of myosin and what do they contain
Head - contains actin binding and ATP binding sites; has ATPase activity
Neck - flexible region, binds myosin LC peptides
Tail - intertwine to bring myosin head regions in close proximity; binds to membrane/organelles
Steps in myosin movement along F-actin of skeletal muscle
- Myosin bound to actin
- ATP binds to myosin head, causing it to release from actin
- ATP -> ADP + Pi which puts myosin in “cocked position”
- Myosin binds to actin
- “Powerstroke” which causes the release of P and energy, causing myosin to straighten and move actin filament when told to do so my electrical impulse
- ADP released, ATP bound, and myosin head releases again
Longer neck domain means what
Increases rate of movement
Steps in myosin in smooth muscle to bind with actin
- Influx of Ca activates the MLC Kinase
- MLC Kinase phosphorylates MLC
- This allows for myosin to unfold and interact with actin
- Action stopped by MLC phosphatase
What forms the contractile ring
Bindles of f-actin and myosin II
What is purpose of actin ring
To create a cleavage furrow
Define DMD
X-linked recessive disorder
Progressive muscle wasting
Usually dead by 22 bc of resp failure
