Cell Bio-Chapter 7 & 8

Question 1

What cytoskeleton consist of?

Answer 1

A network of protein filaments that extends throughout the cytoplasm, providing a structural framework for the cell and serving as a scaffold in determining cell shape & organelle position

Question 2

What does cytoskeleton do for the cell?

Answer 2

1. providing a structural framework for the cell
2. serving as a scaffold in determining cell shape & organelle position

Question 3

characteristics of cytoskeleton:

Answer 3

1. less rigid
2. permanent than its names imply
3. highly dynamic structure
4. continually reorganised as cells move & change shape

Question 4

principal types of protein filaments make up the cytoskeleton

Answer 4

There are 3:
1. actin filaments
2. microtubules
3. intermediate filaments

Question 5

T/F: protein filaments that make up the cytoskeleton are held together and linked to organelles by a variety of accessory proteins

Answer 5

True

Question 6

How does the actin cytoskeleton attach to the cell?

Answer 6

The actin cytoskeleton is similarly anchored to regions of cell-cell contact via
adherens junctions

Question 7

adhesion belt

Answer 7

belt-like structure in sheets of epithelial cells.
connects the underlying bundle of actin filaments to the plasma membrane

Question 8

Cadherins

Answer 8

1. Contact between cells at adherens junctions is mediated by transmembrane
   proteins called cadherins.
2. forms a complex with cantenins and p120 prs.
3. interacts with vinculin( actin & other actin-binding proteins) > anchor actin filaments to plasma membrane

Question 9

T/F: cadherins form a complex with the cytoplasmic Catenins &
p120 protein

Answer 9

true

Question 10

what are the duty of mivrovili?

Answer 10

cell movement, phagocytosis, or other specialized functions

Question 11

T/ F : most of the extension on the surface of the cell are based on actin filaments

Answer 11

true

Question 12

how does the actin filaments are organize in the cell?

Answer 12

either relatively permanent, or rapidly rearranging bundles or networks

Question 13

Microvilli are the best characterized of these actin-based cell surface protrusions &
are abundant on the surfaces of cells involved in absorption (e.g. intestinal
epithelium),where they serve to increase the exposed surface area available for
absorption

Answer 13

true

Question 14

which one is correct?
1. Intestinal microvilli contain bundles of 20-30 actin filaments that are cross-linked by the
actin-bundling proteins fimbrin & villin, which link actin filaments in closely spaced parallel arrays
2. The actin bundles of microvilli are attached
along their length to the plasma membrane
by lateral arms consisting of the Ca2+-
binding protein Calmodulin in association
with myosin I.

Answer 14

both are correct

Question 15

Actin- bundling proteins

Answer 15

fimbrin & villin( they link actin filaments in closely spaced parallel arrays)

Question 16

calmodulin

Answer 16

1. Ca2+- binding protein
2. in association with myosin I , The actin bundles of microvilli are attached along their length to the plasma membrane by lateral arms

Question 17

Extensions and projections of the cell

Answer 17

1. pseudopodia
2. lamellipodia
3. filopodia

Question 18

pseudopodia

Answer 18

extensions of moderate width based on actin filaments cross-
linked into a 3D networks that are responsible for phagocytosis

Question 19

Lamellipodia

Answer 19

broad, sheet-like extensions containing a network of actin
filaments

Question 20

Filopodia

Answer 20

very thin projections of the plasma membrane supported by actin
bundles that extend from lamellipodia

Question 21

stages of cell movement

Answer 21

3 stages :
1. Protrusion such as pseudopodia,
lammelipodia & filopodia must be
extended to establish a leading edge of
the cell. Initial movements of most cells are mediated by the extension of filopodia, which are subsequently
incorporated into lamellipodia.

2. Extensions must attach to the
   substratum across which the cell is moving
3. Trailing edge of the cell must dissociate
   from the substratum & retract into the cell
   body.

Question 22

three stages of cell movement

Answer 22

1. extension of leading edge
2. attachment to substratum
3. retraction of trailing edge

Question 23

small GTP-binding proteins of the Rho family

Answer 23

regulates: The process that underlies the extension of actin filament polymerization against the
plasma membrane at the leading edge in response to signals from other cells or the
environment

Question 24

Rho proteins

Answer 24

1. promote actin polymerisation in coordination with WASP &
   the Plus End-Tracking Protein
2. stimulating the Arp2/3 complex to initiate the growth of branched actin filaments
3. activates formins, and cofilin

Question 25

formin

Answer 25

extend the branched filaments & initiate
linear filaments

Question 26

cofilin

Answer 26

plays an important role in remodeling the
actin network by cleaving existing filaments & providing new plus ends to support
filament branching & growth

Question 27

T/F: Growing actin filaments push
against the plasma membrane &
drive the formation of cell surface
protrusions with considerable
force

Answer 27

true

Question 28

T/f: High local concentrations of ATP-
actin are generated by Profilin,
which makes the growth of actin
filaments energetically favorable.

Answer 28

true

Question 29

What is the result of a high local concentration of ATP-actin generated by profilin?

Answer 29

makes the growth of actin filaments energetically favorable

Question 30

Myosin

Answer 30

1. prototypical molecular motor
2. proteins that convert chemical
   energy in the form of ATP to mechanical energy, thereby generating force &
   movement.

Question 31

skeletal muscles

Answer 31

bundles of muscle fibers, which are single large cells (≈ 50 μm
in diameter & up to several cm in length).
_ most of their cytoplasm is consist of myofibrils

Question 32

myofibrils

Answer 32

cylindrical bundles of thick
myosin filaments (≈ 15 nm in
diameter) & thin filaments of actin
(≈ 7 nm in diameter).
* is organized as a
chain of contractile units called
sarcomeres, which are responsible
for the striated appearance.

Question 33

sacromere

Answer 33

chain of contractile units , Within each sarcomere are A
bands & I bands, with the ends
defined by the Z disc.