Cell Bio-Chapter 7 & 8 Flashcards
What cytoskeleton consist of?
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
What does cytoskeleton do for the cell?
- providing a structural framework for the cell
- serving as a scaffold in determining cell shape & organelle position
characteristics of cytoskeleton:
- less rigid
- permanent than its names imply
- highly dynamic structure
- continually reorganised as cells move & change shape
principal types of protein filaments make up the cytoskeleton
There are 3:
1. actin filaments
2. microtubules
3. intermediate filaments
T/F: protein filaments that make up the cytoskeleton are held together and linked to organelles by a variety of accessory proteins
True
How does the actin cytoskeleton attach to the cell?
The actin cytoskeleton is similarly anchored to regions of cell-cell contact via
adherens junctions
adhesion belt
belt-like structure in sheets of epithelial cells.
connects the underlying bundle of actin filaments to the plasma membrane
Cadherins
- Contact between cells at adherens junctions is mediated by transmembrane
proteins called cadherins. - forms a complex with cantenins and p120 prs.
- interacts with vinculin( actin & other actin-binding proteins) > anchor actin filaments to plasma membrane
T/F: cadherins form a complex with the cytoplasmic Catenins &
p120 protein
true
what are the duty of mivrovili?
cell movement, phagocytosis, or other specialized functions
T/ F : most of the extension on the surface of the cell are based on actin filaments
true
how does the actin filaments are organize in the cell?
either relatively permanent, or rapidly rearranging bundles or networks
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
true
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.
both are correct
Actin- bundling proteins
fimbrin & villin( they link actin filaments in closely spaced parallel arrays)
calmodulin
- Ca2+- binding protein
- in association with myosin I , The actin bundles of microvilli are attached along their length to the plasma membrane by lateral arms
Extensions and projections of the cell
- pseudopodia
- lamellipodia
- filopodia
pseudopodia
extensions of moderate width based on actin filaments cross-
linked into a 3D networks that are responsible for phagocytosis
Lamellipodia
broad, sheet-like extensions containing a network of actin
filaments
Filopodia
very thin projections of the plasma membrane supported by actin
bundles that extend from lamellipodia
stages of cell movement
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.
- Extensions must attach to the
substratum across which the cell is moving - Trailing edge of the cell must dissociate
from the substratum & retract into the cell
body.
three stages of cell movement
- extension of leading edge
- attachment to substratum
- retraction of trailing edge
small GTP-binding proteins of the Rho family
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
Rho proteins
- promote actin polymerisation in coordination with WASP &
the Plus End-Tracking Protein - stimulating the Arp2/3 complex to initiate the growth of branched actin filaments
- activates formins, and cofilin
formin
extend the branched filaments & initiate
linear filaments
cofilin
plays an important role in remodeling the
actin network by cleaving existing filaments & providing new plus ends to support
filament branching & growth
T/F: Growing actin filaments push
against the plasma membrane &
drive the formation of cell surface
protrusions with considerable
force
true
T/f: High local concentrations of ATP-
actin are generated by Profilin,
which makes the growth of actin
filaments energetically favorable.
true
What is the result of a high local concentration of ATP-actin generated by profilin?
makes the growth of actin filaments energetically favorable
Myosin
- prototypical molecular motor
- proteins that convert chemical
energy in the form of ATP to mechanical energy, thereby generating force &
movement.
skeletal muscles
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
myofibrils
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.
sacromere
chain of contractile units , Within each sarcomere are A
bands & I bands, with the ends
defined by the Z disc.
