Cell Anatomy - Cytoskeleton

Question 1

What is the cytoskeleton

Answer 1

System of protein filaments in the cytoplasm that gives a cell shape and the ability for directed movement

Question 2

What are the three types of protein filaments

Answer 2

Microtubules
Actin filaments
Intermediate filaments

Question 3

Rank the protein filaments from most –> least flexible

Answer 3

Intermediate
Actin
Microtubules

Question 4

General properties - filament assembly

Answer 4

Self-assemble from small subunits- allows for rapid assembly/disassembly
Held together by weak, non-covalent bonds

Question 5

How are filaments both stable and dynamic?

Answer 5

breaking a filament in the middle requires breaking many bonds, but requires little energy to remove subunits from the ends

Question 6

What regulates the assembly of filaments?

Answer 6

Accessory proteins

Question 7

Microfilaments dtructure

Answer 7

Globular actin monomers
Actin monomers bind ATP –>
Assemble to form a filament
2 parallel protofilaments twist to form a R helix

Question 8

Do filaments have polarity?

Answer 8

yes

Question 9

What end do filaments grow from?

Answer 9

The plus end

Question 10

What part of the cell are microfilaments usually found?

Answer 10

Near the periphery

Question 11

Microfilaments main functions:

Answer 11

Determine shape of the cell’s surface
Facilitate whole cell locomotion

Question 12

What facilitates the ‘crawling’ of microfilaments

Answer 12

Actin polymerization

Question 13

Microtubules: structure

Answer 13

-Globular tubulin subunits
-Tubulin monomers bind to GTp
-Alpha and beta monomers form dimers
-Protofilaments form hollow cylinder

Question 14

Do microtubules have polarity

Answer 14

Yes. Subunits point in 1 direction, protofilamenst are parallel, grow from plus end

Question 15

Where are microtubules usually located?

Answer 15

-Made in the microtubule organizing center (centrosome)
-Located near the nucleus

Question 16

Main function of microtubules

Answer 16

-Determine the position of membrane-enclosed organelles
-Direct intracellular transport

Question 17

Structure of intermediate filaments

Answer 17

-Rope-like
-assembled from subunits (keratins, neurofilaments, lamins)
-No associated nucleotide
-Alpha helical subunits dimerize into tetrameric subunits
-tetramerics pack together to form protofilament
-8 protofilaments form intermediate filament

Question 18

Are intermediate filaments polar?

Answer 18

No

Question 19

Location of intermediate filaments

Answer 19

Cells that are subject to mechanical stress

Question 20

How are accessory proteins related to the cytoskeleton?

Answer 20

-Crosslink or bundle fibers
-Nucleate filament polymerization
-Cap/block polymerization
-Sever filaments

Question 21

What are motor proteins

Answer 21

-Type of cytoskeleton binding protein
-Move molecules and enclosed organelles in the cell
-Generate the force required for contraction, ciliary movement, and cell division

Question 22

How do motor proteins move

Answer 22

Use ATP hydrolysis to generate mechanical force that allows them to walk along microtubule and microfilaments

Question 23

What are the major types of motor proteins

Answer 23

Myosin
Kinesin
Dynein

Question 24

What are the filaments associated with each motor protein

Answer 24

Myosin - microfilaments (actin)
Kinesin - microtubules
Dynein - microtubules

Question 25

Structure of molecular motors

Answer 25

-head region - binds and hydrolyzes ATP -Tail region - binding site for 'cargo'

Question 26

Kinesin - structure

Answer 26

2 globular head domains

Question 27

Dynein - structure

Answer 27

2 or 3 main proteins plus a variable number of associated polypeptides

Question 28

What is the largest and fastest molecular protein

Answer 28

Dynein

Question 29

Kinesis 'walks' towards which end of the filaments

Answer 29

The plus end

Question 30

Kinesis - how it moves

Answer 30

Hydrolysis of ATP changes conformation of protein, allowing it to walk along the microtubules

Question 31

Dynein - how it moves

Answer 31

Nucleotide hydrolysis + MT binding and unbinding + force generating conformational change Power stroke also driven by ATP hydrolysis, causes head to rotate and generate a step

Question 32

Dynein walks towards which end of the microtubule?

Answer 32

The minus end

Question 33

Kinesin - funtion

Answer 33

Bring cargo to periphery of cell Organelle positioning Axonal transport Mitosis

Question 34

Dynein - funtion

Answer 34

Bring cargo to center of the cell Cilia beating Vesicle transport Mitosis

Question 35

Subunits of microfilaments

Answer 35

Actin

Question 36

Subunits of microtubules

Answer 36

Tubulin

Question 37

Subunits of intermediate filaments

Answer 37

keratin

Question 38

Microfilaments bind...

Answer 38

ATP

Question 39

Microtubules bind...

Answer 39

GTP