Motor Proteins

Question 1

What are motor proteins?

Answer 1

Proteins that bind cytoskeletal filaments and use energy from ATP to move cargo along filaments, includes head region that binds and hydrolyzes ATP and tail region that determines cargo identity.

Question 2

Describe myosin II

Answer 2

composed of 2 heavy and 2 light chains, tail forms coiled coil with another tail, walks toward plus end of actin filament.

Question 3

What are the functions of myosin?

Answer 3

Cell migration, contractile activity in muscle and nonmuscle cells, vesicle and organelle transport, cytokinesis, protrusion of actin rich structures on cell surface, construction of microvilli.

Question 4

what kind of filaments are formed by myosin II?

Answer 4

thick filaments

Question 5

Describe muscles:

Answer 5

involve voluntary movement, myoblasts combine to form a muscle cell containing many nuclei, myofibrils form banding pattern are sarcomeres are the contractile unit.

Question 6

Describe sarcomere structure:

Answer 6

Plus end of actin filaments anchored in Z disc by Cap Z protein. myosin walks toward plus end of actin filament.

Question 7

What occurs during contraction and what does contraction require?

Answer 7

Thick filaments walk toward plus end of thin filaments, it requires ATPase activity of myosin and Ca2+ pumps

Question 8

How does Ca2+ cause muscle contraction?

Answer 8

Voltage gated channel stimulation releases Ca2+ into cytosol, stimulating Ca2+ release channel to release more Ca2+ from sarcoplasmic reticulum and initiate contraction.

Question 9

How does troponin and tropomysosin regulate muscle contraction?

Answer 9

At rest, troponin interferes with tropomyosin positioning so myosin can’t interact with actin. Ca2+ causes tropomyosin to move and myosin binding site to be exposed.

Question 10

Describe the power stroke of myosin:

Answer 10

1. myosin head is attached to actin filament.
2. Another molecule of ATP comes and binds to myosin causing release.
3. Hydrolysis of ATP to ADP and P causes change in position relative to actin filament.
4. Phosphate group is released, causes binding to actin filament by myosin.
5. Power stroke occurs and a molecule of ADP is released.

Question 11

Describe kinesins:

Answer 11

composed of 2 heavy and 2 light chains, plus end directed microtubule motors. Head domain is a motor that consumes ATP, tail domain binds cargo.

Question 12

Describe the kinesin power stroke:

Answer 12

1. lagging head in ATP state, zippers neck linker to throw other head forward to bind microtubule.
2. Lagging head hydrolyzes ATP to ADP + P.
3. After P is released, neck linker unzips and head pulled forward as front head releases ADP and binds ATP and neck linker zippers onto head to pull lagging head forward.

Question 13

Describe dynein:

Answer 13

Minus end directed microtubule motors, composed of 2-3 heavy chains, as well as intermediate and light chains.

Question 14

Describe the power stroke of dynein:

Answer 14

When dynein binds ATP, it releases a microtubule.

Question 15

Describe cilia and flagella:

Answer 15

Motility structures composed of microtubules and dynein.

Question 16

Describe movement of cilia and flagella -

Answer 16

dynein causes microtubule binding, microtubules slide relative to one another.