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Flashcards in Cytoskeleton Deck (62)
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List at least 5 functions of the cytoskeleton

1. organize cells and their environment
2. cell shape
3. Mechanical strength
4. Structures of locomotion
5. Support of plasma membrane
6. Scaffold for spatial organization of organelles
7. Means of intracellular transport of organelles and other cargo


What are the physical properties of microtubules?

tubular (hollow-fiber)
up to many micro meters long
outer diameter of 25nm
flexible (but not resistant to stretching)


What are the functions of microtubules?

- Scaffolds for spatial organization of organelles in cell & cell movment
- Organelle movement
- Movement of cilia and flagella

(usually attached at one end to centrosome or Perinuclear Microtubule Organizing Center (MTOC))


What proteins form microtubules?

Alpha and beta tubulin


Can the GTP bound to the alpha tubulin hydrolyze?



Can the GTP bound to the beta tubulin hydrolyze?



Which end of the alpha-beta tubulin dimer is considered the positive end?

- due to its capability to hydrolyze the GTP


What happens at the + end compared to the - end?

+ end tends to grow
- end tends to shrink


What is the tread-milling phenomenon?

Microtubule (MT) growth at the + end at the same rate as MT disassembly at the - end


What is dynamic instability?

Rapid shrinkage of MT from plus end until GTP containing dimers are added back (the GTP-rich cap)


How do MT capping proteins affect MT stability?

Increase it by protecting or adding GTP cap


Ho dow MT severing proteins affect MT stability?

Decrease it by exposing GDP rick parts
(ex. spastin, katanin)


What are centrioles?

- short cylinders at right angles to eachother
- divide and form mitotic spindle between them during mitosis
- bodies of cilia and flagella


Name 2 drugs that are known to modify MT polymerization dynamics

1. Colchicine (from crocus like flower) - inhibit MT polymerization
2. Vinblastine & Vincristine (madagascar periwinkle) - MT polymerization blockers
3. Paclitaxel (taxol from pacific yew tree) - binds and stabilizes MT's - tubule and tubulin aggregates

***interest in cancer treatment***


Explain the concept of molecular motors

the process whereby MT's used energy from ATP hydrolysis to move cargo along MT in a "walking motion" toward the + or - end (using a mechanochemical cycle)


Which direction does Kinesin take cargo?

Toward the plus end


What motor moves cargo towards the - end?



What are the 3 types of mitotic spindle MT's, and what do they do?

Astral MT:
radiate out from centrosomes

Kinetochore MT:
Attache to kinetochore from centromere of each duplicated chromosome

Overlap MT: interdigitate at the equator of the spindle


Which direction do the MT + ends face?

away from the centrosome


What are flagella?

Long MT's
Propel sperm by undulating motion


What are cilia?

occur in large numbers
on apical surface of various epithelial cells
Beat in whip like motion in wave like pattern=> move fluids over surface of cells (ex. Respiratory tract)


What are the functions of intermediate filaments

Provide intracellular mechanical support


What are the 2 categories of of IF's?

Cytoplasmic IF (including keratins, vimentins and neurofilament proteins)
Nuclear lamins

More heterogeneous than MTs


How do nuclear lamins provide support?

form a meshwork that stabilizes inner membrane of nuclear envelop and anchors chromosomes and nuclear pores


What is the structure of IFs?

elongated molecules
extended central alpha-helical domain
parallel coiled-coil of alpha helixes

Paired diamers associate antiparallel and form staggered tetramers

Tetramers participate in IF polymerization

8 tetramers assemble into protofilaments and pack together laterally to form 1 IF

=> at all levels: IF cross section contains 32individual alpha-helix coils


What is a unique property of IFs?

32 individual alpha-helix coils at each cross sectional area
=> high tensile strength


Where are IFs often located?

intercellular junctions


Name 2 types of IF proteins and where they are located

Vimentins - Majority of cell types

Keratins - dominant components of epidermis and its appendages

Neurofilament proteins - vertebrate axons (controls axonal diameter)

Gilial fibrillary acidic protein (GFAP) - astrocytes in CNS (important in inflamatory/ degenerative processes of brain)


What pathology can result from keratin mutations?

epidermolysis bullosa simplex
- epidermis highly sensitive to mechanical stress (blisters)
- related diseases affecting IFs that anchor filaments in desmosomes have similar symptoms


Name a pahtology related to neurofilaments

Charcot-marie-tooth syndrome
- change in axonal transport of neurofilament subunits
- causes peripheral neuropahty

-abnormal assembly

Progeria syndromes (various)
- mutation in lamin -> nucelar instability