Chapter 14: The Cytoskeleton & Cell Movement Flashcards
the cytoskeleton provides a
structural framework for the cell
the cytoskeleton serves as a scaffold that determines
- cell shape
- general organization
the cytoskeleton is responsible for
movement & cell locomotion
the cytoskeleton transports
organelles & other cell structures through the cell
the cytoskeleton can be described as a
dynamic structure w/ changing architecture
the cytoskeleton localizes the ________ at the center
nucleus
what are the 3 principle types of protein filaments that compose the cytoskeleton?
- actin filaments (microfilament)
- intermediate filaments
- microtubules
actin filaments are aka
microfilaments
what is known as the primary cytoskeleton protein?
actin filaments
actin filaments are helical polymers of
actin protein
actin filaments are organized into a variety of
linear bundles
actin filaments are ___________ throughout the cell, but most concentrated beneath the
- dispersed
- plasma membrane
actin filaments are the smallest filaments that participate in
cell adhesion
actin filaments are not a double helix but instead a
single strand
describe the steps in actin filament assembly
- G actin form dimers
- dimers form trimers
- multiple trimers form F actin filament
the G actin is composed of a
barbed(+) and pointed(-) end
what are the group of proteins involved in the polymerization of actin filaments?
formin
define nucleation
the formation of dimers and trimers
actin monomers bind _____ -> hydrolyzed to _____ following filament assembly
- ATP
- ADP
what is NOT required for polymerization of actin filaments?
ATP
what polymerize more readily than ADP-bound monomers?
ATP-bound actin
define steady state
rate of + end addition = rate of loss from the - end
what is meant by treadmilling?
the net length of the polymer does not change as individual monomers are transferred from one end to the other
what describes the lengthening of actin filaments
increased [] of bound ATP
what describes the shortening of actin filaments
increased [] of bound ADP
actin-binding proteins regulate the
assembly & disassembly of actin
profilin promotes
monomer binding by exchanging ADP for ATP
what acts as a nucleation site to initiate branching of new filaments?
Arp2/3
Arp2/3 is an example of an
actin binding protein
what stabilize actin filaments?
tropomyosin & capping proteins
what cleaves actin filaments
cofilin
cofilin cleaves filaments making new ends for filaments to
polymerize or depolymerize
actin-binding proteins also serve to
organize/stabilize actin filaments
what is the name for the filaments that cross-link actin filaments?
filamen
what form bundles of tightly packed parallel arrays?
fimbrin & α-actinin
actin bundles form what anatomical structure
microvilli
what are known as specialized regions of the plasma membrane that form contacts with adjacent cells or to a surface?
adherens junctions
adherens junction require
actin
what are known as attachment sites for large bundles of actin filaments called stress fibers?
focal adhesions
stress fibers are bundles of
actin filaments linked by α-actin
focal adhesions detach to act as
signal sequences
what links actin to transmembrane proteins of the muscle cell plasma membrane?
dystrophin
what medical condition results from the absence of dystrophin?
Duchenne’s
what medical condition results from abnormal dystrophin?
Becker’s
Duchenne’s and Becker’s syndrome is the progressive degeneration of…and it is ___ linked
skeletal muscle
x
microvilli are
actin bundles in intestinal epithelium
stereocilia are
actin bundles of the inner ear
actin filaments are also involved in
locomotion
give some examples of cell locomotion
- spread of cancer cells
- embryonic cells during development
- WBCs to fight infection
- wound healing
- phagocytosis
define cell crawling
cell locomotion across a surface
list the 3 steps in locomotion
- extension from leading edge
- attachment
- dissociation & retraction
myosin V are
‘two headed’
myosin V transport
organelles & intermediate filaments cargo toward barbed ends of actin filaments
what are known as a large heterogeneous family of proteins?
intermediate filaments
what makes up the nuclear lamina?
intermediate filaments
intermediate filaments span the cytoplasm between
cell junctions
intermediate filaments between cell junctions give ____________ __________ to the cell
mechanical strength
intermediate filaments are NOT
dynamic structures
intermediate filaments give the skin
strength & elasticity
intermediate filaments integrates the components of the
cytoskeleton
intermediate filaments organize the
internal structure of the cell
what is known as the elaborate network in cytoplasm?
intermediate filaments
intermediate filaments extend from a
ring around the nucleus to the plasma membrane
intermediate filaments position
nucleus to the center of the cell
intermediate filaments are NOT involved in
cell movement
intermediate filaments are typically regulated by
phosphorylation
actin filaments are polar but intermediate filaments are
non-polar
intermediate filament dimers are central domains of
2 chains forming coiled-coils
tetramers in intermediate filaments are formed when dimers associate in a
staggered anti-parallel fashion
in order to form protofilaments tetramers assemble
end to end
the final structure of intermediate filaments is composed of
8 protofilaments
intermediate proteins are involved in
NS and epithelium
name the 2 specialized cell contacts that epithelial cells have
- desmosomes
- hemidesmosomes
desmosomes are
junction between cells (cell—–cell)
hemidesmosomes are junctions between
epithelial cells and underlying connective tissue (cell——substrate)
desmosome attachments are mediated by
plakins
what link adjoining cells?
cadherins
examples of hemidesmosomes are
keratin filaments and integrins linked to ECM
Lou Gehrig’s Disease is aka
amyotrophic lateral sclerosis (ALS)
ALS are abnormalities in
neurofilaments
ALS leads to the
progressive loss of motor neurons
ALS results in
muscle atrophy & paralysis
epidermolysis bullosa simplex is the mutation in a
Keratin gene
epidermolysis bullosa simplex causes the development of
skin blisters resulting from cell lysis after minor trauma
what are known as large hollow cylinders of tubulin protein
microtubules
microtubules are more rigid than
actin or intermediate filaments
microtubules are long straight and originate at one end to a single microtubule organizing center known as a
centrosome
microtubule polymerization and depolymerization are involved in
G-protein signaling and vesicle transport
are microtubules dynamic?
YES
microtubules consist of a single type of globular protein known as
tubulin
microtubules determine…
cell shape
microtubules are involved in cell
locomotion
microtubules are also involved in
chromosome segregation
microtubules are hollow cylinders enclosing a
lumen
the wall of a microtubule consists of ____ protofilaments which causes the…
13
closing of microtubule
define a microtubule protofilament
linear polymer of tubulin dimers consisting of 2 polypeptides
what are the 2 polypeptides that compose a microtubule protofilament?
- α-tubulin
- β-tubulin
All ___________ in protofilaments have the same ____________.
heterodimers
orientation
protofilaments associating in the same orientation assigns _______________ to the microtubule
polarity
explain the process of microtubule assembly
tubulin dimers -> oligomers -> protofilament -> sheets of protofilaments -> closing microtubule -> elongating microtubule
similar to actin microtubules can also undergo
treadmilling
microtubule dimers are high in affinity when
bound to GTP
microtubule dimers have a low affinity when
bound to GDP
what end of the microtubule grows away from the centrosome
+ end
when tubulin [] is high tubulin GTP is added to the microtubule tip…
this results in a
faster than the incorporated GTP can be hydrolyzed
GTP cap
the GTP cap helps stabilize….& promote…
stabilize: the microtubule tip
promote: further growth
what occurs at lower tubulin []
- rate of growth decreases
- GTP hydrolysis catches up
no GTP cap being present favors
microtubule polymerization
what regulates the dynamic nature of MT?
microtubule-associated proteins
microtubule-associated proteins track the growth of MT to the
plasma membrane
polymerase microtubule-associated proteins
accelerate growth
depolymerase microtubule-associated proteins
dissociate GTP-tubulin
depolymerase microtubule-associated proteins lead to
catastrophe
what proteins help rescue MT from catastrophe
CLASP proteins
CLASP proteins keep what microtubule-associated protein inactive?
depolymerase
what is known as the MT organizing center?
centrosome
what initiates the polymerization at centrioles
γ-tubulin
what is the direction of MT in dendrites of neurons?
in both directions
what is the direction of MT in axons of microtubules?
in one direction, positive away from nucleus
how can MT grow in both directions in dendrites?
b/c dendrites have ample supply of γ-tubulin
what is the direction of growth of kinesin?
plus end (away from centrosome)
what is the direction of growth of dynein?
minus end (toward centrosome)
kinesin is composed of
2 heavy chains + 2 light chains
dynein is composed of
2-3 heavy chains + multiple light chains
what part of motor proteins bind MTs and ATP?
globular head
how does a motor protein remain inactive until it has cargo to transport?
light chain bends and is on head domain preventing ATP binding & hydrolysis
who demonstrated the motor lock?
Kozielski’s
Kinesin pulls what along the MTs toward the plus end?
ER
kinesin localizes __________ away from the center
lysosomes
dynein helps to position ______________ toward the center
Golgi stacks
what occurs when MTs are depolymerized?
the ER retracts to the center of the cell
microtubules also make what important structures needed for cell movement?
cilia & flagella
MTs extend outward from a
microtubule-organizing center (centrosome)
what occurs before the dissociation of the nuclear envelope?
duplication of centrosomes
MTs aid in the even distribution of
sister chromatids
how is MT organization completely reorganized in mitotic cells?
by rapidly disasembling
kinetochore microtubules
bind to kinetochore
interpolar microtubules aid in
elongating the cell
chromosomal microtubules aid in the
accurate separation of sister chromosomes
astral microtubules aid in
shortening & taking centrosomes apart
what are the 2 distinct mechanisms which chromosome movement occurs?
anaphase a & b
explain anaphase A
- kinetochore MTs shorten
- chromosomes toward spindle poles
- minus end-directed motor protein is involved
explain anaphase B
- elongation of interpolar MTs causes the separation of spindle poles
- overlapping interpolar MTs push poles apart
- astral MTs shorten by motor proteins anchored in the cell mem.
what are critical for cell division?
microtubules
what drugs bind tubulin & inhibit polymerization?
colchicine & colcemid
what drugs inhibit rapidly dividing cells?
vincristine & vinblastine
what drug stabilizes rather than inhibits MT assembly?
taxol
