Contractile Proteins

Question 1

Define actin

Answer 1

A major component of the cytoskeleton

Organized by proteins into diverse structural groups

Question 2

How are actin filaments assembled

Answer 2

Via accessory protein pathways

Question 3

Actin is assembled into what two general types of structures

Answer 3

1. Actin bundles

2. Actin networks

Question 4

Define actin bundles

Answer 4

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

Question 5

Actin bundles can be what or what

Answer 5

Tight or loose

Question 6

What binds to actin filaments within tight actin bundles to hold them together

Answer 6

Fimbrin

Question 7

Give an example of tight actin bundling

Answer 7

Microvilli

Question 8

Define loose actin bundles

Answer 8

Aka contractile bundles

Uses alpha actin

Filaments separated by greater distances

Allows for motor proteins (myosin) to interact during contraction

Question 9

Define network actin bundles

Answer 9

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

Question 10

Mutations in cortical cytoskeleton proteins in RBC is a mutation in what and can cause what

Answer 10

Mutation in spectrin and ankyrin

Can cause hereditary spherocytosis

Question 11

S/S of hereditary spherocytosis

Answer 11

Flexibility and stability of RBCs are impaired

Decreased RBC’s (anemia)

Jaundice
Hepatosplenomegaly

Question 12

Define pseudopodia

Answer 12

Actin projection based on actin filaments cross-linked into a 3D network that are responsible for phagocytosis

Question 13

Define lamellipodia

Answer 13

Broad, sheet like extensions at the leading edge of cell, containing a networks of actin filaments

Question 14

Define filopodia

Answer 14

Thin projections of the plasma membrane supported by actin bundles

Question 15

Define myosin

Answer 15

A superfamily of motor proteins that move along actin filaments via ATP hydrolysis

Question 16

Define Myosin Class 1

Answer 16

1 head with a light chain

Involved in membrane interactions

Question 17

Define myosin Class 2

Answer 17

Aka skeletal muscle myosin

Bipolar filament with two heads

Used in skeletal muscle contraction

Question 18

Define mysoin class 5

Answer 18

4 heads

Used in transport along cytoskeletal actin

Question 19

What are the three domains of myosin and what do they contain

Answer 19

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

Question 20

Steps in myosin movement along F-actin of skeletal muscle

Answer 20

1. Myosin bound to actin
2. ATP binds to myosin head, causing it to release from actin
3. ATP -> ADP + Pi which puts myosin in “cocked position”
4. Myosin binds to actin
5. “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
6. ADP released, ATP bound, and myosin head releases again

Question 21

Longer neck domain means what

Answer 21

Increases rate of movement

Question 22

Steps in myosin in smooth muscle to bind with actin

Answer 22

1. Influx of Ca activates the MLC Kinase
2. MLC Kinase phosphorylates MLC
3. This allows for myosin to unfold and interact with actin
4. Action stopped by MLC phosphatase

Question 23

What forms the contractile ring

Answer 23

Bindles of f-actin and myosin II

Question 24

What is purpose of actin ring

Answer 24

To create a cleavage furrow

Question 25

Define DMD

Answer 25

X-linked recessive disorder

Progressive muscle wasting

Usually dead by 22 bc of resp failure