Cytoskeleton

Question 1

Eukaryotic cells have developed these spatial and mechanical functions in an intricate system of filaments called the

Answer 1

Cytoskeleton

Question 2

The cytoskeleton’s varied functions depend on the behavior of three families of protein molecules which assemble to form three main types of filaments

Answer 2

1) Microfilaments: Actin,
2) Microtubules: tubulin
3) Intermediate Filaments

Question 3

Microfilaments determine

Answer 3

cell shape and locomotion

Question 4

For cells to function properly they must (2)

Answer 4

organize themselves in space and interact mechanically with their environment.

Question 5

Microtubules determine

Answer 5

positions of organelles and direct intracellular transport

Question 6

Intermediate filaments provide

Answer 6

mechanical strength

Question 7

Actin is concentrated inside the

Answer 7

PM (anchors to PM)

Question 8

In a happy and heathy cell the MTs will

Answer 8

extend all the way through the cell into the cortex

Question 9

if a cell is not healthy you will see

Answer 9

retraction of the MTs.

Question 10

Stress fibres

Answer 10

Thick and bundled actin that the cell can use to generate force for movement.

Question 11

Cytoskeletal filaments are

Answer 11

dynamic and adaptable

Question 12

Microtubules are often

Answer 12

in a star-like pattern emanating from the nucleus to the cell periphery

Question 13

Microtubules are a major components of:

Answer 13

-the mitotic spindle during cell division,
-cilia and flagella for cell motility
-Structural pathways for the transport of materials within the cell

Question 14

Actin filaments underlie the ________ and provide ______

Answer 14

PM, provide strength and shape to the thin lipid bilayer

Question 15

Actin filaments also form

Answer 15

many types of cell-surface projections such as lamellipodia and filopodia that cells use to explore territory.

Question 16

The actin-based contractile ring assembles to

Answer 16

divide cells in two.

Question 17

Filopodia is used to

Answer 17

explore territory, they would have receptors on the tips that can interpret their environment.

Question 18

Lamelopodia would be

Answer 18

a sheath that gives the cell the machinery it needs to move. It does this by polymerizing and depolymerizing

Question 19

Intermediate filaments form a

Answer 19

protective cage for the cell’s DNA at the inner face of the nuclear envelope.

Question 20

Intermediate filaments are twisted into

Answer 20

strong cables that can hold epithelial cell sheets together.

Question 21

Intermediate filaments allow (2)

Answer 21

-nerve cells to extend long sturdy axons
-form tough appendages such as hair and fingernails

Question 22

An example of an intermediate filament

Answer 22

Keratin

Question 23

Cells that line the intestine and lung contain

Answer 23

microvilli and cilia (cytoskeletal-based cell surface protrusions) that maintain a constant location, length, and diameter.

Question 24

The cytoskeleton also dictates

Answer 24

cell polarity during the lifetime of a cell.

Question 25

Each type of cytoskeletal filament is constructed from

Answer 25

smaller protein subunits

Question 26

What can small protein subunits do that large filaments cannot

Answer 26

diffuse rapidly across the cytoplasm

Question 27

Actin exists in the cell as

Answer 27

small soluble subunits and as large polymers

Question 28

Intermediate filaments are made up of _____ whereas actin filaments and microtubules are made of ________

Answer 28

smaller subunits that are themselves elongated and fibrous, subunits that are compact and globular (actin subunits and tubulin subunits)

Question 29

What interactions hold subunits together

Answer 29

Non-covalent

Question 30

Nucleation is

Answer 30

rate-limiting step in the formation of a cytoskeletal polymer

Question 31

The tubulin and actin subunits assemble __________ to create _________

Answer 31

head-to-tail, polar filaments

Question 32

Tubulin subunits are heterodimers composed of _________ and ________-- tightly bound together by _________

Answer 32

α-tubulin and β-tubulin, non-covalent bonds.

Question 33

Both α- and β-tubulin monomers have a GTP binding site, but

Answer 33

the GTP in the α-tubulin is trapped at the dimer interface while β-tubulin can have its GTP hydrolyzed to GDP or exchanged for a new GTP. GTP hydrolysis is thus important for microtubule dynamics

Question 34

Longitudinal contact

Answer 34

between α- and β-tubulin

Question 35

Microtubules are the stiffest and straightest structural elements found in most animal cells due to their

Answer 35

high persistence length (the property of a filament describing how long it must be before random thermal fluctuations cause it to bend)

Question 36

The actin subunit is a _______ rather than a _______

Answer 36

Monomoer, dimer

Question 37

Actin subunit binds ____ rather than _____

Answer 37

ATP, GTP

Question 38

Because of the polarity of microtubules and actin filaments their ends

Answer 38

grow and shrink at different pace

Question 39

The fast growing end, as well as the fast shrinking end, is called the

Answer 39

Plus end (+)

Question 40

Whether filaments grow or shrink depend on whether the free subunit concentration is above or below the

Answer 40

Critical concentration

Question 41

The critical concentration is. the

Answer 41

concentration of subunits where the filament grows and shrinks at the same rate= treadmilling

Question 42

Treadmilling and dynamic instability are consequences of

Answer 42

nucleotide hydrolysis by tubulin and actin

Question 43

newly incorporated subunits are in a

Answer 43

T form (GTP or ATP containing)

Question 44

The longer a subunit is incorporated into a filament the more likely it is to be hydrolyzed, therefore in

Answer 44

D form (ADP- or GDP-containing).

Question 45

If the rate of subunit addition is low then the filament tip will be in the

Answer 45

D form

Question 46

D form has a ______ critical concentration than the T form.

Answer 46

higher

Question 47

what happens when the concentration of free subunits is in an intermediate range? That is, lower than the critical concentration of the D form but higher than that of the T form?

Answer 47

Treadmilling

Question 48

In the D form you need ________ subunits available to add to be able to maintain the length

Answer 48

more

Question 49

GTP cap

Answer 49

the rate of hydrolysis was faster than the rate of subunit addition (as it grows we begin to hydrolyze the GTP to GDP, and as this happens if we ran out of available soluble subunits ) (Plus end)

Question 50

Loss of GTP cap

Answer 50

rapid shrinkage at the plus end- this is called MT Catastrophe (rate of hydrolysis faster than rate of subunit addition)

Question 51

MT rescue

Answer 51

as plus end shrunk it would release tubulin dimers, dimers could exchange their GDP for GTP and the concentration of GTP would increase beyond the CC and we would get rapid growth and the GTP would form again

Question 52

When tubulin is GTP bound it is more

Answer 52

stable

Question 53

A GTP bound tubulin specific biochemical structure

Answer 53

Straight

Question 54

GDP bound tubulin in the filament causes

Answer 54

conformational change, slight curvature

Question 55

A MT is made up of ____ protofilaments

Answer 55

13

Question 56

Why continuously spend energy hydrolyzing nucleoside triphosphate?

Answer 56

allows cells to maintain a fluid structure that is primed for a rapid response to external stimuli or the environment.

Question 57

Intermediate filament structure depends on

Answer 57

Lateral bundling and twisting of coiled coils

Question 58

Actin and tubulin is present in

Answer 58

all eukaryotes

Question 59

Intermediate filaments are only present in

Answer 59

some metazoans such as vertebrates, nematodes, and mollusks.

Question 60

Intermediate filaments are predominantly found in cells

Answer 60

exposed to mechanical stress

Question 61

IF assembly

Answer 61

-You have an N terminal and a c terminal, one monomer coils with another monomer, forming a dimer. -Dimer interacts with another dimer forming a staggered tetramer, -They interact head to tail, in that the first dimers N terminal will be closer to the second dimers C terminal, and they interact in this staggered manner. -Two tetramers pack closely together and then 8 tetramers twist into a ropelike structure called a filament

Question 62

Is there directionality and polarity in assembled intermediate filaments

Answer 62

no (nothing can move along, no way to tell which way to go)

Question 63

A second family of intermediate filaments are the

Answer 63

neurofilaments

Question 64

Neurofilaments are found in ____ concentrations along ________

Answer 64

high concentrations along axons

Question 65

Adherens proteins and junction

Answer 65

connect branched actin to next cell, giving it strength from cell to cell (in epithelial cells)

Question 66

Desosomes

Answer 66

Connections between cells via IF, provide stability and strength to cells and therefore lining of bl vessel or intestine

Question 67

Why is minus end of MTs toward apical and plus end towards basal surface

Answer 67

Cellular machinary can move things in proper direction -ex. blood vessel: apical side next to inside of vessel where blood will be, cell needs to move nutrient s from blood into cells and epithelial layer

Question 68

Cytoskeleton maintains _________ of cell that allows specialized cells to perform their functions

Answer 68

Polarity

Question 69

Filaments formed from multiple __________ have advantageous properties

Answer 69

protofilaments

Question 70

Nucleation experiment what happens to soluble actin subunits when adding salt

Answer 70

They polymerize

Question 71

Lag phase

Answer 71

Nucleation

Question 72

Growth phase

Answer 72

Elongation

Question 73

Equilibrium phase

Answer 73

Steady state

Question 74

Steady state

Answer 74

same number of subunits coming off the actin filament that you are adding to the other end

Question 75

Concentration at which steady state occurs

Answer 75

critical condition

Question 76

What happens if we added oligomers at the neginning (nucleation experiment)

Answer 76

Reach critical concentration in less time, same rate of growth, build fibril faster, bypass nucleation step

Question 77

What happens if you fully depolymerize actin

Answer 77

The rate at which you could build a new fibril would reduce

Question 78

Lateral contact

Answer 78

α-α and β-β

Question 79

What do lateral and longitudinal contacts do

Answer 79

Strengthen microtubules

Question 80

Structure of MT: where is GTP present

Answer 80

Both the alpha and beta subunit

Question 81

GTP in the alpha subunit(MT)

Answer 81

Buried in the core to make the interactions between 2 units very strong

Question 82

GTP in the beta subunit

Answer 82

readily accessible for hydrolysis

Question 83

Alpha and beta subunits bind to eachother to form ________ which gives structure

Answer 83

protofilaments polarity

Question 84

What do protofilaments have on their ends

Answer 84

A plus end and a minus end

Question 85

The GTP of what subunit is readily accessible for hydrolysis

Answer 85

beta

Question 86

Polymerization will happen more readily at the

Answer 86

plus end

Question 87

It is slower to add a subunit to the minus end because it is in

Answer 87

D form

Question 88

What happens to MT when you lose GTP bound cap

Answer 88

Fraying, no strength at end (less interactions), less energy needed to break bonds

Question 89

Amyotrophic lateral sclerosis is associated with the

Answer 89

Accumulation and abnormal assembly of neurofilaments in motor neuron cell bodies and in the axon