C6: Cytoskeleton Flashcards
A ___ is present in the cytoplasm of all cells, including bacteria, and archaea
cytoskeleton
It is a complex, dynamic network of interlinking protein filaments that extends from the cell nucleus to the cell membrane
cytoskeleton
It gives the cell its shape and mechanical resistance to deformation, and through association with extracellular connective tissue and other cells it stabilizes entire tissues.
cytoskeleton
The ___ is the collective name for all structural filaments in prokaryotes
prokaryotic cytoskeleton
play essential roles in cell division protection, shape determination, and polarity determination in various prokaryotes.
Cytoskeletal elements
Prokaryotic cytoskeleton (5)
FtsZ
MreB
CRESCENTIN
ParM and SopA
MinCDE system
The first identified prokaryotic cytoskeletal element, forms a filamentous ring structure located in the middle of the cell called the Z- ring that contricts during cell division.
FtsZ
acts as an organizer protein and is required for cell division; homologous to eukaryal tubulin
FtsZ
is a bacterial protein believed to be analogous to eukaryal actin
MreB
determines cell shape by mediating the position and activity of enzymes that synthesize peptidoglycan and by acting as rigid filament under the cell membrane that exerts outward pressure to sculpt and bolster the cell.
MreB
condenses from its normal helical network and forms a tight ring at the septum in Caulobacter crescentus right before cell division.
MreB
is also important for polarity determination in polar bacteria, as it is responsible for the correct positioning of at least four different polar proteins in C. crescentus.
MreB
____ (encoded by ___ gene) is an analogue of eukaryotic.
Crescentin; creS
has a rather large primary homology with IF proteins in addition to three-dimensional similarity
Crescentin
is a cytoskeletal element that possesses a similar structure to actin, although it behaves functionally like tubulin.
ParM
___ and ___ that are responsible for R1 plasmid separation.
ParR; parC
is a filament system, that properly
positions the septum in the middle of the cell in Escherichia coli.
MinCDE system
inhibits the formation of the septum by prohibiting the polymerization of the Z-ring.
MinC
_____ form a helix structure that winds around the cell and is bound to the membrane by MinD.
MinC, MinD, and MinE
function is for the maintenance of cell-shape by bearing tension;
INTERMEDIATE FILAMENTS
Organise the internal tridimensional structure of the cell, anchoring organelles and serving as structural components of the nuclear lamina.
INTERMEDIATE FILAMENTS
also participate in some cell-cell and cell matrix junctions.
INTERMEDIATE FILAMENTS
are most commonly known as the support system or “scaffolding” for the cell and nucleus while also playing a role in some cell functions.
Intermediate filaments
form cell-cell connections and anchor the cell-matrix junctions that are used in messaging between cells as well as vital functions of the cell.
intermediate filaments
intermediate filaments are in general present in mesenchymal cells.
Vimentin
is present in general in epithelial cells.
Keratin
type of IF giving structural support to the nuclear envelope
lamin,
, play an important role in structural and mechanical support of muscle cells
desmin
All intermediate filaments start from a fibrous subunit. This then coils around another filamentous subunit to form a coined-coil ___
dimer, or protofilament
Using proteins called ___, the intermediate filaments can be connected to one another to form sheets and meshes
plectins
can also connect the intermediate filaments to other parts of the cytoskeleton, while other proteins can help to attach the IF cytoskeleton to the cell membrane (e.g., desmoplakin)
Plectins
aid in cytokinesis and cell motility; Involved in cytoplasmic streaming
microfilament
They are also part of muscle cells and allow these cells to contract, along with myosin.
microfilament
Cytoskeletal opposites of the intermediate filaments
ACTIN FILAMENTS
They are strands are made up of small globular actin (g-actin) subunits.
ACTIN FILAMENTS
the largest of the
cytoskeleton’s fibers at about 23 nm.
MICROTUBULES
hollow tubes made of alpha and beta tubulin
MICROTUBULES
Most of the microtubules in an animal cell come from a cell organelle called the
centrosome
important in forming
the spindle apparatus (or mitotic spindle)
microtubules
involved in transporting molecules within the cell and in the formation of the cell wall in plant cells.
microtubules
Microtubule are mostly found as large 13-stranded (each strand is called a ____) hollow tube structures.
protofilament
Dimers of ____ polymerize to form microtubules
α- and β-tubulin
a phenomenon in microtubules wherein, tubulin subunits will both associate and dissociate from the plus end of the protofilament.
Dynamic Instability
__ is fairly strong, but not very flexible; Depolymerization also occurs.
microtubule
almost all microtubules have their (-) end in a perinuclear area known as the
MTOC, or microtubule organizing center.
MTOC contains a structure known as the __.
centrosome
components of centrosome (2)
centriole-
pericentriolar material (PCM)
- two short barrel-shaped microtubules based structures positioned perpendicular to each other
centriole
facilitates microtubule nucleation
Y-tubulin ring complex
“railroad tracks”= ___
“trains” = ____
“railroad tracks”= microtubules
“trains” = kinesins and dyneins
“streets”= ___
“trucks”= ___
“streets”= microfilament
“trucks”= myosin
____ drive towards (+) end or cell periphery
____ go toward (-) end or towards the MTOC
KINESINS
DYNEINS
an arrangement of alternating fibers of f-actin (“thin fibers”) and myosin II (“thick fibers”).
SARCOMERE
Sarcomere is one of many connected together to form a __ (extends the length of mucle cell).
myofibril
are responsible for muscle contraction.
Sarcomeres
a fibrous protein that lies in the groove of an actin microfilament and blocks access to the myosin binding site.
TROPOMYOSIN
attaches to the microfilament in conjunction with a multi-subunit troponin complex.
TROPOMYOSIN
- calcium binding protein subunit that initiates the sequence of conformational changes on the thin filament
Troponin-C
a gigantic protein (the largest known, at nearly 3 MDa); can be thought of as something of a bungee cord tether to the myosin
TITIN
prevent the forces generated by the myosin from pulling the fiber apart
TITIN
Nerve cell releases neurotransmitters such as ___ which bind to receptors (AChR) on the muscle cell.
acetylcholine (ACh),
Membrane attachment to the cytoskeleton is necessary for
force transmission.
Signaling from membrane receptors can induce cytoskeletal rearrangements via
adapter proteins.
were one of the early experimental systems for studying cytoskeleton-membrane interactions.
Erythrocytes
__ and __ are important linkage proteins connecting transmembrane proteins to microfilaments.
Ankyrin, spectrin
are used to connect extracellular substrates to the cytoskeleton and enhance signal transduction.
Scaffolding proteins
control cytoskeletal polymerization, depolymerization, bundling, and network formation.
Accessory proteins
promotes actin polymerization by exchanging ATP with ADP and enhancing addition to microfilaments
Profilin
regulates microfilament assembly by sequestering G-actin and releasing it via profilin.
Thymosin B4
___ and ___ can sever actin microfilaments by altering subunit conformation.
Gelsolin and severin
___ and __ are microtubule-severing proteins
Spastin and katanin
sequesters tubulin dimers and is regulated by phosphorylation.
Op18 (stathmin)
__, ___, and ___ promote microtubule assembly and stability.
MAP1, MAP2, and tau
Several proteins crosslink (6)
F-actin, fimbrin, alpha-actinin, b-spectrin, dystrophin, and filamin.
the ability of an organism to move independently, using metabolic energy.
MOTILITY
is genetically determined, but may be affected by environmental factors.
MOTILITY
refers to an organism’s ability to move food through its digestive tract.
MOTILITY
responsible for protrusion of the front end of migrating cells.
RAPID POLYMERIZATION
accounts for the ability of cells to migrate in a specific direction.
CHEMOTAXIS
Cellular swimming: Their beating pattern is then coordinated at the cellular level, most often in a wave-type of manner known as the
metachronal wave
Other strategies of swimming include the elegant movement used by Eutreptiella - called .
metaboly
2 types of cell motility
cell swimming
cell crawling
is the common mechanism employed by most eukaryotic animal cells as they move through animal tissues, constituted of other cells or filaments of the extracellular matrix.
Cell crawling
They either move by means of wormlike cycles of extensions and contractions of their cell body or of some specific protrusions, or slide without visible means of protrusion, a process also referred to as gliding.
cell crawling
slide without visible means of protrusion, a process also referred to as .
gliding
The best characterized crawling mechanism is the so called
amoeboid motility.
Two-dimensional protrusions
lamellipodia,
filopodia or microspikes
Flat veil-shaped projections called ___, as they
occur keratocytes’ in fibroblasts’ or fish motility for wound healing.
lamellipodia
Long thin projections called either ____, and which occur for example in neuronal growth-cone progressions.
filopodia or microspikes
process of amoeboid motility can be decomposed into three to five steps that occur simultaneously
- Extension
- Adhesion
- Translocation
- De-adhesion
The first process opf amoeboid motility is ____, where the membrane is pushed forward by means of the polymerization of cytoskeletal filaments.
Protrusion
Then the protrusion adheres to the __ via the formation of ___, and subsequent contraction of the cellvvcytoskeleton drags the cell body forward.
substrate; anchoring points
are dynamic events that occur within the cytoskeleton of eukaryotic cells.
Microtubule growth and catastrophes
The ____ refers to their
ability to alternate between phases of growth and shrinkage
dynamic instability of microtubules
___, also known as actin-based gels or actin networks, are dynamic and organized structures formed by a protein called actin.
Actin gels
Actin can exist in two primary forms:
globular (G-actin) and filamentous (F-actin).
are involved in cell motility, including processes like crawling, muscle contraction, and the formation of cellular protrusions
Actin gels
in the cytoskeleton refers to the movement of cellular structures and organelles within a cell that is powered by motor proteins associated with the cytoskeleton.
Motor-driven motility
____ explain various biophysical processes.
These models involve the movement of proteins, ion transport, and rotary-motor processes.
Isothermal rectifying models
