The Cytoskeleton Flashcards
the cytoskeleton provides strength and shape, playing a central role in movement and division by driving and guiding intracellular ???
organelle traffic
Microtobulues are hollow or solid tubes?
hollow
microtubules are formed from ??? dimers and are 25nm big
tubulin
microfilaments are a double helix made of ??? monomers and are about 7nm big
actin
intermediated filaments are a strong fibre composed of ??? subunits and are 8-12nm big
protein
what is an example of the cytoskeleton’s ability to rapidly reorganise?
a fibroblast
TRUE or FALSE: the cytoskeleton is responsible for large-scale cellular polarity which allows cells to tell the difference between top, bottom or front and back
TRUE
what is the largest structural element of the cytoskeleton?
microtubules
microtubules are rigid and typically have one end attached to a ???
microtubule-organising centre
cytoplasmic microtubules pervade the cytosol and are responsible for maintaining/altering cell shape, placement and movement of vesicles, formation of mitotic and meiotic spindles and ???
maintaining axons
are axonemal or cytoplasmic microtubules responsible for placement and movement of vesicles?
cytoplasmic MTs
what part of the cytoskeleton is responsible for the formation of mitotic and meiotic spindles?
cytoplasmic Microtubules
axonemal or cytoplasmic Microtubules include he organised and stable microtubules in structures such as cilia/flagella and the basal bodies to which they attach
axonemal
the basic subunit of a microtubule protofilament is a heterodimer of ???
tubulin
microtubules are composed of one alpha tubulin and one beta-tubulin bound COVALENTLY or NON-COVALENTLY to each other?
non-covalently
are all the dimers of microtubules or intermediate filaments oriented the same way?
microtubules
how do microtubule protofilaments have an inherent polarity?
because of dimer orientation
microtubules are hollow cylindrical structures built from 13 parallel ??? of tubulin protein
protofilaments
microtubules will self-assemble in-vitro but ??? is the rate limiting step
nucleation
nucleation of microtubules creates a ring structured microtubule seed for growth but this is slow. More commonly seeded by ??? ring in microtubule organising centre to be speedier
gamma-tubulin ring
microtubules originate from ??? within the cell. Centrosomes near the nucleus and basal bodies near the cell membrane in cilia/flagella
microtubule-organising centres
microtubules grow outwards from microtubule-organising centres with a fixed polarity where the MINUS or PLUS (?) ends are anchored in the MTOC
minus ends
dynamic growth and shrinkage of microtubules occurs at the PLUS or MINUS end?
plus
MTs form by the reversible polymerisation of dimers in the presence of ??? and Mg2+
GTP
what is a unique property of microtubules?
their ability to constantly polymerise and depolymerise i.e. dynamic instability
microtubule binding proteins modulate filament dynamics and ??? and can also mediate the interaction of microtubules with other cell components. i.e. tau proteins
organisation
microtubule targeting agents interfere with ??? and alter equilibrium between subunits
tubulin assembly/disassembly
TRUE or FALSE: Disruption of microtubules induces various cellular responses often
leading to cell cycle arrest or cell death
True
an example of a microtubule targeting agent is ??? which comes from a yew tree and binds along filaments to stabilise them
taxol (paclitaxel)
an example of a microtubule targeting agent is ??? which comes from an autumn crocus and caps both filament ends to depolymerise the microtubule
colchicine
microtubules allow for nutrient transport in neurons. Tau helps support these microtubules, but hyperphosphorylated Tau forms affrefates, dissociating from MTs and staving the neurons = ???
alzheimers
Microfilaments are helical polyemers of actin that are flexible and are dispersed throughout the cell but most concentrated in the ??? beneath the plasma membrane
cortex
microfilaments develop and maintain ??? and are involved in cell migration and cytoplasmic streaming.
cell shape
what is the structural core of microvilli?
microfilaments
microfilaments are composed of actin subunits that are a 375-amino-acid polypeptide carrying a tightly associated molecule of ??? or ???
ATP or ADP
microfilament actin subunits assemble head to tail to form a ???
protofilament
two microfilament protofilaments form a helix held together by ??? contacts
lateral
like tubulin, the actin protofilaments composing ??? have polarity and the ends differ chemically and structurally
microfilaments
Globular‐actin (G-actin) monomers REVERSIBLY or IRREVERSIBLY (?) polymerise into actin microfilaments (“F‐actin”). G‐actin is added rapidly at the plus end and slower/lost at the minus end. G‐actin monomers nucleate slowly but then can assemble onto MF more rapidly, bound ATP is then slowly hydrolysed to ADP. Growing MF ends have ATP‐actin, whereas most of the MF is composed of ADP‐actin
reversibly
G-actin is added rapidly at the PLUS or MINUS end of a microfilament and slower at the opposite end
plus
subunits of ??? cycle rapidly between free and filamentous states and have the ability to maintain a constant length despite a net flux of subunits through the polymer
microfilaments
treadmilling of microfilaments occurs at a subunit concentration where filament growth balances ??? Requires ATP hydrolysis for energy
shrinkage
what type of energy does treadmilling of actin filaments require?
ATP Hydrolysis
actin binding proteins influence filament dynamics and organisation. E.g. ??? stimulates filament elongation
profilin
TRUE or FALSE: the role of microfilaments can be determined through chemical inhibition that can be used to unsettle microfilaments
TRUE
lactrunculin is a drug that ??? by binding to actin subunits. Originally found from sponges
depolymerises
cytochalasin B depolymerises actin by capping the filaments ??? ends. comes from fungi
plus
phalloidin stabilises acting by binding along filaments. Comes from the ???
amanita mushroom
Mutations in the skeletal muscle α‐actin gene (ACTA1) may affect its ??? binding ability and cause a range of congenital myopathies. People with actin-accumulation myopathy have severe muscle weakness (myopathy) and poor muscle tone (hypotonia) throughout the body
e.g. Floppy baby syndrome
ATP
intermediate filaments are the most stable component of the cytoskeleton, conferring strength on tissues. they are rope-like fibers with a ??? diameter
10nm
intermediate filaments are assembled from basic structural units consisting of two intermediate filament ??? intertwined into a coiled-coil
polypeptides
the two dimers of intermediate filaments are ???
aligned in parallel
parallel dimers align laterally to form a tetrameric protofilemt which overlap to build a filamentous structure ~8 protofilaments thick. Intermediate filaments or microfilaments?
intermediate filaments
types of intermediate filaments can be:
- nuclear (lamins)
- Vimentin-like (vimentin, desmin)
- epithelial (???)
- axonal (neurofilament proteins)
keratin
A single epithelial cell can produce multiple
types of keratins which co‐polymerise into a single network held together by ??? bonds
disulfide
??? impart mechanical strength by anchoring the intermediate filaments at sites of cell–cell and cell matrix contact – desmosomes and hemidesmosomes
keratins
epidermolysis bullosa simplex: Occurs when defective keratins are expressed in the ??? of the epidermis. Results in the skin blistering to even mild mechanical stress
basal cell layer
