Cytoskeleton Flashcards
3 y/o m/c lab with large “cauliflower-like” mass on base of penis
history - owners adopted six weeks before from a rescue, bloody penile discharge intermittently since adoption
Biopsy - large round cells with moderate mitotic acticity and mild anisocytosis and anisokaryosis
Diagnosis?
canine transmissible venereal tumor
Cytoskeleton - how are cells organized and what are the categories?
organized and held together by a set of structural proteins that are divided into three categories
microtubules, microfilaments, intermediate filaments
What is cytoskeleton important for?
cell shape, motility, strength, processes, polarization, signaling, organelle organization, movement of macromolecules, and membrane organization
Microtubule structure
hollow tubes around 24 nm in diameter, often centered around nucleus radiating outward, alpha exposed at negative end while tubulin is exposed at positive end, i guess -/+ are not charges
alpha end is more likely to..
regress
beta end is more likely to…
grow
where are microtubules found?
general cytoplasmic organization, mitotic spindle, axons and dendrites, cilia
microtubule functions
cell scaffolding and polarization, polarized movement of organelles, proteins, and dna
Resists compression
microtubule transport
What are the two motor proteins and where do they move?
polarized tubules and allow polarized movement. Two motor proteins - kinesin (toward positive end, move something away from the center), dynein (toward negative end, move something toward center). Bind to cargo and “walk” down the tubules
microtubule regulation - nucleation
what increases assembly?
What are the two major nucleation sites?
What do the nucleation sites contain?
microtubules are slow to assemble. Introducing a template drastically increases MT assembly. Nucleation sites - centrosomes and basal bodies, both contain gamma-tubulin
Microtubule regulation - nucleation
Nucleation polarizes what?
Where are minus ends anchored and where do positive ends grow?
nucleation polarizes microtubule assembly. Minus ends are anchored in the centrosome and positive ends grow toward periphery.
what determines polarization of MT?
location and number of centrosomes
MT regulation - dynamic instability. Where do tubulin dimers bond? What does B-tubulin hydrolyze? High concentration of GTP dimer do what? Low concentration of GTP-bound dimers do what?
tubulin dimers must be bound to GTP to bind to the + end of MT
B-tubulin slowly hydrolyzes GTP to GDP
High concentrations of GTP-dimer in solution promote MT growth and stability.
Low concentration of GTP-bound dimers in solution promote MT catastrophe and collapse
What does dynamic instability do overall
Uses up energy but allows rapid regulation of MT network
What are MAPs and what can they do?
Microtubule associated proteins, can stabilize, destabilize, cause bundling, cause branching of MT structure and cause interaction with other cytoskeleton fibers or cell junctions and can also move protein or organelles along the MAT
Microfilament structure
double helical fibers, found throughout the cell but mostly toward periphery, only one subunit, actin assembles into a polarized strand
Microfilaments found in..
cell cortex, microvilli and stereo-cilia, lamellipodia, filopodia, and muscle fibers
primary functions of microfilaments
cell membrane organization, ameboid movement, muscle contractions, and cytokinesis
Resists stretching
What does polarization allow for microfilaments?
What are the MF motor proteins?
Myosin head bind to what and hydrolyzes what?
ATP hydrolysis causes..
polarization allows polarized transport
MF motor proteins are myosins
Myosin head that binds to actin filaments and hydrolyzes ATP
ATP hydrolysis causes a change in shape in the myosin molecule, pushing it along the microfilament.
ATP hydrolysis causes what which causes what
causes a change in shape in the myosin molecule, pushing it along the microfilament, this movement is used to move vesicles, protrude membranes, contract the cell
muscle fibers are organized how?
specialized and densely organized fibers of actin and myosin
What can actin binding proteins do in MF regulation?
stabilize MF, destabilize MF, encourage MF polymerization, cap MF< cause bundling of MF, crosslink MF, Nucleate/cause branching of MF, Bind MF to membrane/ecm, and generate force along MF
Different Microfilament regulation ways
Dynamic instability/tread milling, nucleation, and actin binding proteins.
what are intermediate filaments made of?
fibrous (non-globular) proteins, the long fibrous proteins bundle and twist together into rope like structures
