Cell Motors

Question 1

the cytoskeleton is mae up of what 3 things

Answer 1

microtubules, microfilaments, and

intermediate filaments

Question 2

actin filaments can form?

Answer 2

filopodia, lamellipodia,

microvilli, stress fibers

Question 3

what are motor proteins

Answer 3

molecular motors that bind to a polarized cytoskeletal filament
and use the energy derived from repeated cycles of ATP hydrolysis to move steadily
along it

Question 4

what is the purpose of myosins

Answer 4

cause cytoskeletal filaments to slide against each other, generating the force
that drives muscle contraction

Question 5

what is the function of kinesins and dyneins

Answer 5

carry membrane-enclosed organelles to their appropriate
locations in the cell.
Dyneins are responsible for ciliary beating and flagellar waves.

Question 6

what are microtubules

Answer 6

hollow rods
for:
- shaping the cell
– guiding movement of organelles
– separating chromosomes during cell division
- they grow out from a centrosome (MTOC)

Question 7

what is the centrosome?

Answer 7

it is the MTOC, has a pair of centrioles which each have 9 triplets of microtubules

Question 8

what are microfilaments

Answer 8

- solid rods, built as
a twisted double chain of actin
subunits.
Function is to bear tension. They form a cortex to support cell shape.
They make up microvilli

Question 9

what are intermediate filaments?

Answer 9

• fibrous proteins supercoiled into thick cables
• proteins are of the keratin family
• maintain cell shape, anchor nucleus and organelles, form nuclear lamina

Question 10

cytoskeleton filaments are x and y

Answer 10

dynamic and adaptable

Question 11

give examples of self assembled structures

Answer 11

cytoskeleton filaments, virus coats,
bacterial flagella, protein machines. Also, pathogenic protein aggregates
(hemoglobin-S polymers, prions, Alzheimer’s plaques)

Question 12

what is a polar filament?

Answer 12

Each asymmetric subunit points in the same
direction (orientation). The two ends are topologically different, therefore
the resulting filament lattice has inherent directionality.

Question 13

what is a non polar filament

Answer 13

Polypeptides are always asymmetric, but they
can polymerize into filaments where both ends of the composing
subunits are topologically equivalent, therefore the resulting lattice has
no inherent directionality

Question 14

what are the implications of filament polarity?

Answer 14

Proteins that bind a filament will
adopt the same orientation(Only polar filaments can act as
directional tracks for motor proteins)
Different protein surfaces are
exposed at the two ends
– End-specific nucleation
– End-specific capping

Question 15

what is the preferred end for subunit addition of microtbules

Answer 15

+ end

Question 16

what structure acts as tracks for movement of vesicles?

Answer 16

microtubules, Golgi
and lysosomes move towards minus ends
while secretory vesicles move towards plus ends

Question 17

what is the preferred end for adding on subunits for actin?

Answer 17

actin filaments are organized
with their barbed ends pointing forwards. As the membrane protrudes,
new actin subunits polymerize onto these barbed ends

Question 18

What is G-actin?

Answer 18

(globular actin), with
bound ATP, can polymerize to
form F-actin

Question 19

what is F-actin?

Answer 19

may hydrolyze bound
ATP  ADP + Pi
and release Pi
ADP is not released from the
filament because the nucleotide
binding pocket is closed in Factin.

Question 20

what is the purpose of G-actin?

Answer 20

can release ADP and bind ATP, which

is usually present at higher concentration than ADP in the cytosol.

Question 21

the cleft of actin monomers faces

Answer 21

towards the minus end

Question 22

actin filaments may undergo treadmilling, which is?

Answer 22

in which filament length remains approximately constant, while actin monomers add at the (+) end and dissociate from the (-) end.

Question 23

what are the 3 groups of actin binding proteins?

Answer 23

banding and cross-linking proteins

regulatory proteins, motor proteins (myosin)

Question 24

give examples of regulatory protein

Answer 24

Profilin: controls turnover of the G actin pool
Thymosin b4: regulates actin polymerization by sequestering G actin subunits
Formin: assists actin polymerization in cooperation with profilin
Tropomodulin: Prevents dissociation
of the filament into
monomer subunits

Question 25

what is the function of actin-binding proteins such as a-actinin, villin and fimbrin

Answer 25

bind

actin filaments into parallel bundles.

Question 26

filamins dimerize to form

Answer 26

V shaped cross-linking proteins that
are inherently flexible, organize actin filaments
into loose networks, may also have scaffolding roles

Question 27

structure of myosin II

Answer 27

two heavy chains acids long and four light chains, The light chains are of two distinct types, and one copy of each type
is present on each myosin head. Dimerization occurs when the two
α helices of the heavy chains wrap around each other to form a
coiled-coil, driven by the association of regularly spaced
hydrophobic amino acids. The coiled-coil arrangement makes an
extended rod in solution, and this part of the molecule is called the
tail

Question 28

myosin V is involved in

Answer 28

vesicle and organelle transport

Question 29

kinesins walk towards

Answer 29

the + end of a microtubule

Question 30

what are dyenins

Answer 30

minus-end-directed microtubule motors,

Question 31

what are the 2 kinds of dyenins?

Answer 31

cytoplasmic dyneins, which are
typically heavy-chain homodimers, with two large motor domains as heads. Cytoplasmic dyneins are probably found in
all eucaryotic cells, and they are important for vesicle trafficking, as well as for localization of the Golgi apparatus near
the center of the cell.
Axonemal (ciliary) dyneins, the other large branch, include heterodimers and heterotrimers, with two or three motordomain heads, respectively. They are highly specialized for the rapid and efficient sliding movements of microtubules
that drive the beating of cilia and flagella.

Question 32

can dyenin act on its own?

Answer 32

it need accessory proteins, like actin-related protein Arp1, spectrin and ankyrin

Question 33

what is the common structure of cilia and flagella

Answer 33

a core of microtubules sheathed by the plasma membrane
– a basal body that anchors the cilium or flagellum
– dynein, which drives the bending movements of a cilium or
flagellum