Lecture 19- Actin Filaments

Question 1

What is the subunit of Actin Filament/ F-actin

Answer 1

Globular actin/ G-Actin

Question 2

How do F-Actins assemble themselves?

Answer 2

Treadmilling

At (-) end they fall off and at (+) end is where they are added.

Question 3

Difference of treadmilling in Actin and Dynamic instability in Microtubules

Answer 3

Treadmilling: (+) end grows and (-) shrinks

Dynamic instability: (+) end grows and shrinks

Question 4

What stops treadmilling fron happening in cells?

= There are many ___-binding proteins

Answer 4

Actin

Question 5

If you want to organize F-actin into structure, actin-binding proteins must bind in the _____

Answer 5

Middle

Question 6

If you want actin filament to stop growing, the actin-binding proteins should bind at the ___- end

Answer 6

Plus end

Question 7

If you want actin filaments to be smaller, actin-binding proteins should cut in the ____

Answer 7

Middle

Question 8

If you want actin filament to grow, (grow longer and won’t shrink) actin-binding proteins should bind at the ___ end

Answer 8

Minus end

Question 9

ARP Complex (Nucleating Protein)

Answer 9

Anchors the (-) end, allow the (+) end to griow longer and longer.

ARP Complexed can be free or attached to other F-actins.

Question 10

Two ways ARP Complexes can grown an actin filament

Answer 10

1. It can sit by itself and grow an actin filament
2. It can connect to the side of an actin filament and grow another one in a new direction.

Question 11

ARP Complex is both a nucleating protein and an acting-binding protein that can bind in the middle

True or False

Answer 11

TRUE

Question 12

F-Actins can form 1D, 2D, or 3D structures

True or False

Answer 12

TRUE

Question 13

Why is F-actin stability desirable?

Hint: intestine cells

Answer 13

Microvilli (which is an actin filament) increases the surface area of intestine cells.

Question 14

Two important Actin-binding proteins that contribute to the stability of F-actin (both of them bind in the middle of actin filaments)

Answer 14

1. Cross-linking proteins (Filamin)- organizes actin filaments into crosses to make up the cell cortex.
2. Bundling proteins (Villin-in the microvilli) - holds actin together.

Question 15

What are the three Actin-binding proteins and their function

Answer 15

1. Nucleating- allow growth of F-actins
2. cross-linking - holds F-actins into meshes to make up the cortex
3. Bundling- holds F-actins into parallel bundles

Question 16

Which of these is similar in function to gammaTuRC? (Nucleates MT formation)

A. G-Actin
B. ARP Complex
C. Filamen
D. Villin

Answer 16

ARP complex

Question 17

What are actin filaments made of?

Answer 17

Made of G-actin that has been assembled into F-actin strands

Question 18

How are actin filaments organized in immobile cells, for example intestinal epithelial cells?

Answer 18

Organizes actin filaments into crosses (Filamin) or bundle them (Villin)

Question 19

How are actin filaments organized in cells that crawl, for example amoeba?

Answer 19

Make actin filaments in new random direction

Question 20

If you were to use fluorescently labeled antibodies to determine the location of the gamma Tubulin in a human cell you would find it:

A. On the surface of the centrosome
B. Inside the centrosome
C. Along the length of each microtubule
D. At the tips of growing microtubules
E. At the tips of shrinking microtubules.

Answer 20

On the surface of the centrosome