Lecture 15

Question 1

What are the 3 types of Cytoskeleton filaments?

Answer 1

Actin filaments

Microtubules

Intermediate filaments

Question 2

Describe actin filaments in terms of their subunits, the pattern they form, their diameter, and the structural characteristics of it.

Answer 2

(mardi gras beads) Composed of Actin subunits that are assembled into two-stranded helical polymers that create flexible structures that are approximately 5-9 nm in diameter

Determine the shape of the cell’s surface and are involved in whole-cell locamotion, secretion, and endocytosis

Question 3

Describe microtubules in terms of their subunits, the pattern they form, their diameter, and the structural characteristics of it.

Answer 3

(slinky) composed of tubulin subunits that are assembled into long hollow cylinders that have one end attached to a centrosome, and create a more rigid (than actin) structure who’s outer diameter is approximately 25 nm

Make up centrioles and mitotic spindle

Found in cilia and flagella however they lack function in cilia and cystic fibrosis

Question 4

Describe intermediate filaments in terms of their subunits, the pattern they form, their diameter, and the structural characteristics of it.

Answer 4

(building girders) made of small fibrous subunits arranged in a “staggered” pattern, forming rope-like fibers 10 nm in diameter, that allows the filaments to tolerate bending and stretching.

These are strong fibers that provide mechanical strength that resists mechanical stress and are involved in cell-cell junctions that strengthen the epithelial sheet.

Question 5

Dynamic instability predominates in _________

Answer 5

microtubules

Question 6

Describe the polymerization and depolymerization of actin filaments.

Answer 6

actin subunits form actin filaments via covalent protein contacts

ATP-actin polymerizes and ADP-actin disassembles

Question 7

Describe the polymerization and depolymerization of microtubules.

Answer 7

Tubulin subunits form microtubules via noncovalent protein contacts

Both subunits alternate and each microtubule is composed of 13 protofilaments aligned in parallel with “alpha to beta” bonds as well as “alpha to alpha” and “beta to beta” bonds

Question 8

______ and ________ both form via a combination of end-to-end and side-to-side protein contacts. describe the ends of these filaments.

Answer 8

actin filaments ; microtubules

Has a fast growing plus end and a slow growing minus end

Question 9

Describe intermediate filaments in terms of tetramer structure

Answer 9

each tetramer is composed of monomers, arranged in a parallel coiled-coil dimer with another monomer in an antiparallel manner (N to C and C to N)

Question 10

Define a coiled-coiled dimer of intermediate filament monomers

Answer 10

2 monomers, each with their own alpha-helical domain, coiled around each other facing the same direction (n to n and c to c)

Question 11

describe one intermediate filament monomer

Answer 11

an elongated molecule with an alpha-helical domain

Question 12

describe the hierarchal arrangement of monomers to eventually form intermediate filaments.

Answer 12

2 alpha helical monomers parallel forms a dimer

2 dimers antiparallel form a staggered tetramer

8 tetramers parallel form intermediate filaments

Question 13

Intermediate filaments have no binding site for ______

Answer 13

a nucleotide (this is unlike actin filaments and microtubules that bind to ATP/ADP and GTP/GDP respectively)

Question 14

____________ is the rate limiting step of cytoskeletal filament assembley

Answer 14

nucleation

Question 15

what does the polymerization of protein subunits create in a filament?

Answer 15

structural polarity

Question 16

define actin and tubulin

Answer 16

they are both enzymes that catalyze ATP to ADP and GTP to GDP respectively

Question 17

Define Nucleation

Answer 17

the process by which the initial aggregate, or nucleus, of a filament forms

Question 18

Define Catastrophe

Answer 18

the change from growth of the filament to rapid shrinkage

Question 19

Define Rescue

Answer 19

the change from rapid shrinkage of a filament to growth

Question 20

Describe treadmilling

Answer 20

When subunits are being added to the plus end and falling off of the minus end of the filament in such a way that the total length of the filament is not changed by the simultaneous adding and removing of subunits.

Question 21

in what types of filaments does treadmilling predominate?

Answer 21

actin filaments

Question 22

Define nucleoside hydrolysis

Answer 22

the process that occurs when monomer subunits bound ATP/GTP are hydrolyzed to ADP/GDP shortly after being polymerized.

The plus end tip of the polymer remains in the T form (unhydrolyzed) as a cap, and each monomer makes it’s way to the minus end via treadmilling, where it will by hydrolyzed to the D form.