Contractile Proteins

Question 1

Actin bundles

Answer 1

assembled via accessory proteins; cross linked into closely packed parallel arrays; Have POLARITY

Question 2

Actin networks

Answer 2

loosely crosslinked in orthogonal arrays to form a 3D meshwork with gel-like properties

Question 3

Actin-Bundling proteins

Answer 3

cross linking of F-actin achieved by polypeptides with at least two actin binding sites; typically small ridged proteins that force the filaments to align closely with each other

Question 4

Closely spaced actin filaments in a bundle that are parallel; helps increase surface area

Answer 4

projections such as microvilli

Question 5

Binds to actin filaments as a monomer, holding two parallel filaments CLOSE together

Answer 5

fimbrin

Question 6

Reason for loosely bundled actin filaments; less cross linking

Answer 6

contraction; contractile rings in mitosis

Question 7

binds to actin as a dimer; filaments are separated by a greater distance allowing motor protein (myosin) to interact during the contraction

Answer 7

alpha-actinin

Question 8

holds actin filaments in networks together; binds actin as a dimer with binding locations on opposite ends; can create a 3D meshwork; maintains structure and function of membranes

Answer 8

filamin

Question 9

Role of spectrin

Answer 9

binds to actin as tetramer forming an actin network on the cytoskeleton; interacts with ankyrin and protein 4.1

Question 10

actin filaments crosslinked to 3D network that are key in phagocytosis

Answer 10

Pseudopodia

Question 11

broad, sheet-like extensions of actin at leading edge of cell with actin network

Answer 11

Lamellipodia

Question 12

thin membrane projections supported by actin BUNDLES; formation and retraction is based on assembly/disassembly of the actin filaments

Answer 12

Filopodia

Question 13

How does myosin move along actin filaments

Answer 13

ATP hydrolysis

Question 14

Myosin head

Answer 14

ATP binding and ATPase; actin binding

Question 15

Myosin neck

Answer 15

flexible, binds myosin light chain peptides

Question 16

Myosin Tail

Answer 16

intertwine to bring myosin head regions together and bind membranes/organelles

Question 17

Class I myosin

Answer 17

membrane association and endocytosis

Question 18

Myosin II class

Answer 18

contraction of muscles

Question 19

Class V myosin

Answer 19

organelle transport

Question 20

Myosin pathway

Answer 20

binding of ATP causes actin release; binding of actin again causes release of Pi to drive the power stroke, moving the actin filament; remains bound til ADP/ATP switch

Question 21

Smooth muscle contractions

Answer 21

myosin folds over itself (no troponin etc.) when low Ca2+; when Ca2+ goes up, myosin light chain kinase is activated which phosphorylates myosin light chain; myosin can then unfold and interact with actin

Question 22

Non muscle contractions

Answer 22

several actin-myosin structures similar to skeletal; cytokinesis has bundles of F-actin and myosin II forming contractile ring; movement along ring creates the cleavage furrow

Question 23

cell migration

Answer 23

actin at leading edge (lamellipodia) moves forward and extends projections by adding actin to plus end