Contractile Proteins

Question 1

What are actin bundles?

Answer 1

F-Actin that is cross-linked into closely packed parallel arrays by peptides/polypeptides

Question 2

What are actin networks?

Answer 2

Actin that is loosely cross-linked in orthogonal arrays that form three-dimensional meshwork with gel-like properties

Question 3

What are actin-bundling proteins?

Answer 3

Proteins that bind cross-linking F actin

Question 4

What does fimbrin do?

Answer 4

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

Question 5

What are contractile bundles?

Answer 5

Actin i laments that are loosely bundled

Question 6

What does alpha-actinin do?

Answer 6

Binds as a diner to separate filaments by a greater distance; allows for loose bundling

Question 7

What does filamin do?

Answer 7

Large actin binding proteins; Binds actin as a dimer; binds actin filaments in networks

Question 8

What does spectrin do?

Answer 8

Binds actin to create a mesh network to form a cytoskeleton (interacts with ankyrin and protein 4.1)

Question 9

What is hereditary spherocytosis and its clinical manifestations?

Answer 9

A mutation in cortical cytoskeleton proteins in erythrocytes (spectrin, ankyrin, protein 4.1)

Decreased RBC (anemia)
Jaundice
Splenomegaly

Question 10

What is pseudopodia?

Answer 10

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

Question 11

What is lamelliopodia?

Answer 11

An actin projection that is a broad, sheet like extension at the leading edge of a cell, containing a network of actin filaments

Question 12

What is filopodia?

Answer 12

A thin actin projection of the plasma membrane supported by actin bundles. The formation and retraction of these structures is based on the regular assembly and disassembly of actin filaments

Question 13

What does myosin use to fuel movement?

Answer 13

ATP hydrolysis

Question 14

What are the three major domains of myosin?

Answer 14

Head, neck and tail

Question 15

Which myosin domain contains acting binding and ATP binding sites?

Answer 15

The head

Question 16

Which myosin domain is the flexible region/binds myosin light chain peptides?

Answer 16

The neck

Question 17

Which myosin domain binds membrane/organelles

Answer 17

The tail

Question 18

Describe how myosin moves along F-actin?

Answer 18

In absence of ATP, myosin attaches to an actin filament

Binding of ATP causes a conformational change, releasing actin

Myosin remains in a cocked state until binding to actin

Binding of actin causes release of phosphate to drive power stroke (conformational change in the neck and moves actin filament)

Remains bound until ADP/ATP switch

Question 19

How does the velocity of a longer neck compare to a shorter myosin neck?

Answer 19

A longer neck will have increased velocity

Question 20

A low concentration of calcium correlates to what?

Answer 20

A folded state of myosin; relaxed state of muscle

Question 21

A high concentration of calcium correlates to what?

Answer 21

Phosphorylation of myosin, causing it to unfold and become active

Question 22

What causes cleavage furrow in cytokinesis?

Answer 22

Myosin movements along actin filaments of the contractile ring

Question 23

Myosin V binds to what to become active?

Answer 23

Cargo

Question 24

What is duchenne muscular dystrophy? And what causes it?

Answer 24

A progressive muscle wasting disease (x-linked recessive)

An out of frame mutation in the dystrophin gene which normally connects the cytoskeleton to the basal Lamina