Lecture 3

Question 1

What are microfilaments / actin filaments?

Answer 1

Microfilaments are long strands of globular protein β-actin (G-actin)

Question 2

_____ polymerizes forming filamentous _____

Answer 2

G-actin polymerizes forming filamentous F-actin

Question 3

Is there polarity in Microfilaments?

Answer 3

Yes

Question 4

What are the factors influencing the rate of growth and shrinkage of microfilaments?

Answer 4

1.) Concentration of G-actin
2.) Capping proteins increases length by stabilizing minus end

Question 5

What is Filopodia?

Answer 5

Finger-like projections produced by polymerization of actin.

Question 6

What motor protein(s) work with Microfilaments?

Answer 6

Myosin

Question 7

What is Lamellipodia?

Answer 7

Sheetlike projections produced by polymerization of actin.

Question 8

What is a myosin?

Answer 8

Myosin is an ATPase. It transforms energy associated with ATP hydrolysis into mechanical energy.

Question 9

What are the distinct regions of Myosin?

Answer 9

Head, Neck, Tail

Question 10

Which myosins are used for cargo transport?

Answer 10

Myosin 1 and Myosin 5

Question 11

Which myosins are used for muscle tissue?

Answer 11

Myosin 2

Question 12

Directionality of Myosin Movement.

1.) Which direction do most Myosins move toward?
2.) What is the name of the myosin that moves towards the opposite direction of most myosins?
3.) What is the function of the myosin in question 2?

Answer 12

1.) Most known types of myosin move towards the (+) end
2.) Myosin 6 / moves towards (-) end
3.) Function of myosin 6 = Intracellular and endocytosis

Question 13

What are the two aspects to remember about proteins?

Answer 13

1.) Proteins can change shape when compounds bind to them
2.) Changing shape can allow proteins to bind or unbind other compounds

Question 14

What two basic processes underlie the sliding filament model?

Answer 14

1.) Chemical = Myosin binds to actin (Cross-bridge)
2.) Strucutral = Myosin bends (Power stroke)

Question 15

What are the 5 stages of the cross-bridge cycle?

Answer 15

1. ATP binds, causing myosin to detach
2. Detachment of myosin causes ATP to be hydrolyzed to ADP and Pi, which remain bound by myosin
3. Hydrolysis causes myosin to attach to actin
4. Release of phosphate promotes power stroke
5. ADP is released

Question 16

What is an Unitary Displacement?

Answer 16

The distance that myosin steps during each cross-bridge cycle

Question 17

What is a Duty Cycle?

Answer 17

The proportion of time during each cross-bridge cycle that myosin is attached to actin.

Duty Cycle = (time spent in cross-bridge)/(time for full cross-bridge cycle)

Question 18

What is the typical duty cycle for a non-muscle myosin?

Answer 18

0.50 = 50%

Question 19

What is the typical duty cycle for a muscle myosin?

Answer 19

0.05 = 5%