Cytoskeleton Flashcards
Intermediate filaments
(8-10nm), rope like, made of various proteins, functions in the structural component of the cell.
Anchors at sites of stress, connected at desmosomes & hemidesmosomes.
Monomers: Keratin (epithelium), Vimentin (nonepithelial), Neurofilament (neurons)
Not polar, not free, and no associated motor proteins (not involved involved in cell movement)
Keratin
Skin in higher animal contains an extensive network of intermediate filaments made of protein
keratin, which is largely responsible for the toughness of this protective outer covering. Epidermolysis bullosa simplex (EBS) is caused by mutations in keratin genes resulting in abnormal assembly of keratin filaments in the epidermis. As a result, the skin is highly vulnerable to mechanical injury and even a gentle pressure can rupture its cells, causing the skin to blister. a sheet of epithelial lacking intermediate filaments; under the
mechanical stress, the cell sheet becomes damaged.
Epidermolysis bullosa simplex (EBS)
Skin in higher animal contains an extensive network of intermediate filaments made of protein
keratin, which is largely responsible for the toughness of this protective outer covering. EBS is caused by mutations in keratin genes resulting in abnormal assembly of keratin filaments in the epidermis. As a result, the skin is highly vulnerable to mechanical injury and even a gentle pressure can rupture its cells, causing the skin to blister. a sheet of epithelial lacking intermediate filaments; under the mechanical stress, the cell sheet becomes damaged.
Amyotrophic Lateral Sclerosis (ALS, knows as Lou Gehrig’s disease)
Amyotrophic lateral sclerosis (ALS, known as Lou Gehrig’s disease) has been suggested to be a result of mutations in neurofilaments. Abnormal accumulation and assembly of neurofilaments cause progressive loss of motor neurons, which in turn leads to muscle atrophy, paralysis, and eventual death. Although the mechanism involved remained to be understood, current research data suggests the involvement of neurofiliaments in pathogenesis of motor neuron disease including ALS.
Microtubles
(20-25nm) Hollow cylinders. functions in intracellular transport via motor proteins, chromosome segregation, cilia and flagella.
Anchors: MTOC (centrosome, minus end), capping proteins (plus ends), spindle poles, basal body of cilia and flagella.
IN THE CELL THEY GROW & SHRINK ON THE + SIDE of the Microtubules.
Binds to nucleotides GTP and has GTP catalytic activity. Does have structural polarity (+ and - end)
monomers: alpha and beta tubulin. it does have a bound and unbound form (dynamic instability) and its associate motor proteins are kinesin (+ends) and dynein ( - ends)
Actin
(6-8nm) double stranded helical shape. functions in stucure microvillus, lamelloipodi and filopedia for movement, muscle contraction. Anchors at adherens junctions and focal adhesions. Binds to the nucleotide: ATP (has ATP hydolytic activity. Monomer: G-actin. it is structurally polar (plus and minus ends), it does have bound and unbound form (dynamic instability) and associated with Myosin I and II motor proteins
Dynamic instability of microtubules (more detail)
The dynamic instability of microtubules results from the hydrolysis of GTP-bound beta-tubulin during or shortly after polymerization, which reduces its binding affinity for adjacent molecules. Growth continues as long as there is high concentration of tubulin bound to GTP. New GTP bound tubulin molecules are then added more rapidly than GTP is hydrolyzed, so a GTP cap is retained at the growing end. The GTP cap is a transitory structure that is dependent on the levels of GTP-tubulin. However, if GTP is hydrolyzed more rapidly than new subunits are added, the presence of GDP-bound tubulin at the plus end of the microtubule leads to rapid disassembly and shrinkage.
Dynamic instability of microtubules
increase [GTP-tubulin heterodimers] = add them faster than hydrolysis forming a GTP cap on the growing end, favors growing.
When [GTP-tubulin heterodimer] is low, GTP naturally gets hydrolye, the GTP cap is no longer there, (GTP hydrolysis is faster than new subunits being added) = rapid shrinking
Capping proteins vs. GTP cap
GTP cap is a transient structure (dynamic instability of microtubules) GTP cap forms when [GTP-tubulin herodimer] is high and stabilizes the + end of microtubules. capping proteins (are real physical proteins) are found on the inner leaflet, and they hold on the microtubules originating from the MTOC (- end) and they hold onto the the + end of the microtubules. This gives the cell polarity. Motor proteins use these as a track.
Kinesin
has ATPase activity, transports vesicles and organelles towards the plus ends, which extend towards the cell periphery.
Dynein
has ATPase activity carries its cargos towards the minus ends, which are anchored in the center of the cell
Dynein (axonemal)
is the motor protein found in cilia and flagella (which are made out of microtubles)
axonemal dynein deficiency (Kartagener syndrome)
absence of dynein in flagella and cilia results in their immotility and leads to male sterility and chronic respiratory infection
Dynamic instability of Actin filaments
Assembly and disassembly of actin filaments: Polymerization of actin filaments is controlled by ATP binding and hydrolysis. ATP binding favors polymerization, while ATP hydrolysis favors depolymerization.
Actin filament structures
1) microvilli and filopodia: parallel bundles (connected by a protein)
2) stress fibers at focal adhesions: contractile bundles
3) cell cortex (made of a network of actin filaments and associated actin binding proteins. cell cortex determines cell shape and is involved in cell movement: Shape: Networks (criss-crosses and pins holding them together.
