cytoskeleton features Flashcards
the cytoskeleton is made up of 3 structures, which are…
Microfilaments (7nm), intermediate filaments (8-10 nm), and microtubules (25 nm)
Actin: how many genes do I have? What are my varieties?
6.
4 are expressed in muscle cells and 2 in non-muscle cells.
alpha-actin (found in muscle)
beta-actin (non-muscle actin)
gamma (non-muscle actin)
T/F: Actin does not bind directly to transmembrane proteins?
False: it binds directly or indirectly
Actin monomers = ___? Actin filaments = ____ ?
G-actin and F-actin
“Treadmilling” refers to-
equilibrium between polymerization and depolymerization of G-actin to F-actin
Low concentrations of G-actin favor what process?
depolymerization
High concentrations of G-actin favor what process?
polymerization
What end of F-actin does G-actin polymerize most quickly?
the plus (+) end, barbed
the “slow” moving end of F-actin is called the
minus ( - ) end, the pointed end
Cytochalasins
Prevents elongation, interrupts mitotic spindle: does job by binding to + end of f-actin
Phalloidin
Binds to actin filaments and prevents their depolymerization
Fluorescent-labeled phalloidin is used to stain actin filaments in cells
Latrunculins
Disrupts actin polymerization by binding to g actin and inducing f-actin depolymerization
Profilins
Has two functions: can exchange ADP for ATP on G-actin, favoring polymerization at barbed end OR it can prevent G-actin from polymerization by holding on to molecule monomer
“Suppresses nucleation”
Cofilin
An actin depolymerization factor: stimulates dissociation of ADP bound g-actin
Triggers depolymerization at the minus end
Thymosin
Sequesters pools of g-actin monomers within a cell.
Gelsolin
Dual role: capping protein to prevent loss and addition of actin monomers; a severing protein
Destabilizes f actin and caps actin filaments, preventing loss and addition of g actin
Spectrin
RBC relation actin binding protein, connects cytoskeleton to plasma membrane
Dystrophin
Connects cytoskeleton to plasma membrane
Villin and fimbrin
Cross connecting proteins in microvilli
Calmodulin
Cross links actin filaments to microvilli cytoplasm
Myosin 1
Cross links actin filaments to microvilli cytoplasm
Alpha actinin
Cross links stress fibers and connects actin to cytoplasm complexes
Filamin
Cross links actin at wide angles to form screen like gels
Parallel bundles
Closely spaced f-actin fibers with the same polarity
Contractile bundles
Utilizes alpha actinin: actin fibers spaced widely apart, cross connected by alpha actinin
What causes nucleation?
Random collisions, which explains the high rate of polymerization when concentrations of actin are high
What stabilizes actin as formins nucleate along unbranched stretches of f-actin?
tropomyosin
Intermediate filaments are ___ thick, and are ___ in all cells subject to ___________
8-10 nm, abundant, mechanical stress
What do intermediate filaments do per say?
Provide tensile strength in cells such as neurons and muscle
IF: All have a common monomer consisting of-
a central alpha helical rod flanked by a head and tail domain
I consist of repeating amino acid segments: what am I, what’s my name?
intermediate filament, “heptads”
Coiled-coil alpha helix dimers OR parallel _________. What am I?
intermediate filaments
Structure of the intermediate filaments (5 levels)
a. polar filament monomer (N end/C end) align like polar groups, forming a DIMER
b. dimers align in antiparallel fashion, forming a TETRAMER
c. tetramers coil around one another to form PROTOFILAMENTS
d. protofilaments align to form PROTOFIBRILS
e. 4 protofibrils coil together to form a 10 nm thick intermediate filament
What aspect of intermediate filaments allow them to bind to other elements in the cytoskeleton?
the N terminal and C terminals
T/F
The formation of a nonpolar helical structure consisting of two nonpolar antiparallel tetramer requires ATP to occur.
F, no ATP involved. Spontaneous.
IFAPS: What am I, what is my role, and how might I operate?
Intermediate filament associated proteins (IFAPS)
Stabilize filaments by cross linking adjacent filaments or by linking to other cytoskeletal elements
May cap filaments to prevent further elongation
IFAPS: list ‘em
Filaggrin (associated with keratin) Epinemin Paranemin Plectin Synemin
Synemin
IFAP
Epinemin
IFAP
Filaggrin
IFAP, associated with keratin
Plectin
IFAP
Paranemin
IFAP
Type I IF Type
Acidic Keratins
along with basic to neutral keratins, these form the intermediate filaments of the epithelial cell cytoskeleton
Acidic Keratins
form the intermediate filaments of the epithelial cell cytoskeleton
associated with plaques of desmosomes and hemidesmosomes
Type II
Basic Keratins, along with acidic keratins they form the intermediate filaments of the epithelial cell cytoskeleton
Vimentin
Type III IF, found in mesenchymal cells
Desmin
Type III IF, associated with sarcomeric Z-discs
Glial fibrillary acidic protein
Type III IF associated with astrocytes and Schwann cells (glial cells)
Peripherin
Type III IF associated with neurofilaments
Neurofilaments
Type IV IF, found in axons and dendrites
Nuclear Lamins
Type V nuclear lamins: provide mechanical support for inner membrane of nuclear envelope and bind chromatin
Nestin
Type VI IF associated with CNS stem cells
Microtubules are ____ in width, and composed of ____ and _____
25 micrometers
alpha (negatively charged end) and beta (positively charged)
A “protofilament” in the microtubulin category consists of
a longitudinal row of tubulin
Microtubules are composed of
alpha and beta tubulin dimers strung together to form long rows of them
A microtubule is composed of
13 protofilaments arranged parallel to form a cylinder with a hollow core
13 is the magic number for what molecule?
microtubules: the number of protofilaments in a “microtubule”
Dynamic instability refers to
“alternating phases of slow growth and rapid depolymerization”
What causes dynamic instability?
the hydrolysis of GTP tubulin dimers, which release GDP dimers subunits
MAPs —->
microtubule associated proteins: increase stability of microtubules
Factors that inhibit microtubule polymerization—>
colchicines, colcemid, vincristine, and vinblastin: bind to tubulin monomers and inhibits polymerization
Factors that inhibit depolymerization and stabilize microtubules
taxol: binds to microtubule and inhibits depolymerization
Cilium: structure
9 peripheral doubles + central pair of microtubules
Each doublet consists of
alpha tubule: this consists of 13 protofilaments, radial spokes extending to sheath around central pair, and pairs of dynein arms projecting to beta unit of next doublet
alpha tubule
consists of 13 protofilaments, radial spokes extending to sheath around central pair, and pairs of dynein arms projecting to beta unit of next doublet
beta tubule
10-11 protofilaments
13 protofilaments = the
alpha tubule
10-11 protofilaments = the
beta tubule
which protofilament has the dynein arm stretching to its neighbor?
the alpha
which protofilament contains spokes which radiate toward the sheath around the central pair?
the alpha
rod like portion refers to what cytoskeletal component and what is it called
IF, formed by polymerization of long, rod like elements
coiled-coil alpha helix dimers or parallel intermediate filament proteins
referred to as “heptad”
