Flashcards in Week 4 Cytoskeleton Module Deck (51):
The structural components of cells are collectively known as...
What is the cytsokeletons' fxn 2?
support the cell, aid in movement of the cell
what are the three different types of cytoskeletal filaments?
intermediate filaments (IF), microtubules (MT), actin filaments (AF)
Describe the appearance of intermediate filaments
what is the role of IF?
resist mechanical stress
which filament type is the toughest and most durable?
where are IF found?3
cytoplasm; surround the nucleus and extend out to cell periphery
Desmosomes: cell-cell jxns
Nucleus: form meshwork beneath nuclear envelope (nuclear lamina formed by nuclear lamins)
Sinlge alpha-helical monomer-->Two monomers associate to form a coiled-coil dimer-->two dimers associate (in opposite directions) to form a staggered tetramer-->eight tetramers assemble side-by-side to make a short bundle-->short bundles assemble end to end to make long rope-like filament
which filaments have polarity?
Actin filaments and microtubules do, but IF do not. This is because of the fact that IF dimers associated in opposite directions
what two cells have an abundance of IF? why?
epithelial cells of skin (stratified squamous) and muscle cells. These cell types undergo a great deal of mechanical stress
what are the classes of IF (4)? and location
keratin filaments (ALL epithelial cells, cytokeratin), vimentin filaments (connective tissue cells, muscle cells), neurofilaments (nerve cells), nuclear lamins (foudn in nucleus of ALL animal cells)
ALL IF except lamins are found in cytosol
what is the role of nuclear lamins?
type of IF that forms strong meshwork in the nucleus; involved in nuclear organization, cell-cycle regulation, differentiation, gene expresion
What is epidermolysis bullosa simplex? cause? symptoms?
mutation in skin-specific keratin gene (IF) that causes skin blistering under little mechanical pressure
Progeria: cause? symptoms?
mutation in gene encoding for lamin A, lamin A cannot provide structural support for the nucleus (gene expression, cell division impacted)
Symptoms: limited hair growth, wrinkling of skin, kidney problems, MSK degeneration, Cardiovascular issues
Microtubules general appearance
hollow rods with distinct ends
general role of MT? 2
act as railroad tracks in which vesicles, organelles, and other cellular components can be moved,
also form core in cilia and flagella
composition of MT
made up of alpha and beta tubulin dimers. these dimers stack on each other (end to end) to form protofilament chains. 13 parallel protofilament chains form MT
Describe polarity of MT
one end has alpha tubulin exposed (- end) and the other end has beta tubulin (+ end) exposed
what is significant about the +/- ends of MT?
this does not relate to charge. Refers to the fact that dimers are added much more quickly to the + end than the - end (+ end grows faster)
what is a centrosome? what is embedded in it? directionality?
a microtubule organizing center that microtubules grow out of. The + end is exposed and the - end of the MT is buried within gamma-tubulin rings of the centrosome
consists of a pair of centrioles surrounded by matrix protein (including gamma-tubulin rings)
what are basal bodies?
centrioles that acts as organizing centers for MT in the cilia (lung, epithelial)
what are mitotic spindles?
the structure of MT seen during cell division that are organized by centrosomes and are responsible for dividing chromosomes
define dynamic instability of MT. Role?
the ability of MT to either polymerize or depolymerize very rapidly. this is a way for MT to "explore" the cell for binding partners
MT stabilize (no longer exhibit dynamic stabiliy) when...
they attach to specific proteins or other cell components
Describe the polymerization/depolymerization of MT
+ end binds GTP. If a/b tubulin subunits are added faster than GTP is hydrolyzed (GTP cap) then the MT will grow. If GTP is hydrolyzed (GDP) before a/b tubulin is added, the MT will shrink
why might cancer researchers want to target MT for cancer treatment?
cancer cells proliferate faster than the normal cell. By stabilizing the MT (preventing chromosome separation) or preventing polymerization (cant attach to chromosomes) cell division halts
cancer drug that stabilizes MT (prevents them from depolymerizing)
Colchicine and Vinblastine: effect?
cancer drug that prevent polymerization of MT
what is the relationship between motor proteins and MTs?
MT are the tracks in whcih motor proteins move to deliver their cargo
what are the two major types of motor proteins?
Kinesins and dyneins
what is the major role of kinesin?
moves cargo (organelles, vesicles, macromolecules) toward the plus end of the MT (periphery of cells)
what is the major role of dyneins? (2)
move cargo toward negative end of the MT (toward toward centrosome,
centrosomes are generally located near....
nucleus of cell
what accounts for the movement of cilia and flagella?
the stable MT core is moved by dyneins
what is the microfilament arrangement seen in flagella?
9 + 2 array: 9 MT doublets around the outside with 2 single microtubules in the center.
what are the two primary roles of actin filaments?
movement and cells shape
how are AF formed?
polymerization of single actin monomers into two-stranded hleix
actin monomers can bind ATP. Free actin monomers carry ____ that is ____ upon incorporation into the filament
what shapes can actin filaments adopt? 3
contractile ring (pinches off in dividing cells)
microvilli: increase SA
Contrast Cilia and Microvilli
Composed of? location? relative size? fxn?
Cilia: made of MT, respiratory tract, larger, motile (move substances along)
Microvilli: made of AF, digestive tract, smaller, non-motile (increase SA)
treadmiling is a term associated with...
describe AF polymerization/depolymerization
actin filaments have a fast-growing plus end and a slower-growing minus end. growth is also ATP dependent
what is treadmilling?
actin (-) end is not associated with an organizing center like MT and can therefore shrink or grow at BOTH ends. treadmilling refers to the adding of subunits at + end while removing them at eh - end
do Actin filaments undergo dynamic instability like MT?
no, AF can control rates of pol/depol
what is the most abundant protein in eukaryotic cells?
what are the two types of protrusions made by actin filaments that assist in cell migration?
lamellipodia (broad) and filopodia (thin)
what is the actin motor protein?
What is myosin II fxn?
produce a contractile force by pulling on actin filaments (muscle contraction, contraction of non-muscle cells (stress fibers))
the shapes that actin takes within a cell is regulated by...
monomeric GTPases known as Rho GTPases