The Cytoskeleton Flashcards
Actin Filament Morphology
Two-stranded alpha helical polymers found most concentrated in the cortex just beneath the plasma membrane
Microtubule Morphology
Long, hollow cylinders made up of the protein tubulin. At the minus end it contains a MTOC (centrosome) which doesn’t allow for any alteration of the minus end
Intermediate Filament Morphology
Ropelike fibers. One type of intermediate filament forms a meshwork called the nuclear lamina.
Functions of Actin
Serves to increase surface area of the cell through the microvilli. It is involved in muscle contraction. It is also involved in cell-cell adhesion through adhesion junctions and cell-matrix adhesion through focal contacts.It assists in cell motility through the lamdellipodia and it is also involved in phagocytosis.
Functions of Microtubules
Serves as the basis for the mitotic spindles which is very important for the separation of chromosomes in DNA replication. It participates in vesicle transportation through the ER and the transportation (either anterograde-Golgi to plasma membrane, or retrograde- plasma membrane to Golgi). It is also involved in cell motility through the use of flagella and cilia.
Functions of Intermediate Filaments
They serve as to help maintain the cell and tissue integrity and for mechanical strength. It is also involved in cell-cell adhesion through desmosomes and cell-matrix adhesion through hemidesmosomes. It is involved in axon diameter and strength and in nuclear lamins by increasing nucleus integrity.
Actin Subunits
Actin monomer (soluble) attached to ATP and actin polymer attached to ADP.
Actin polymerization
ARP caps the minus end of the actin polymer while CapZ caps the plus end of the polymer.
Rho Family- Rho addition
Causes the rapid assembly of the stress fibers.
Rho Family- Rac
Causes the formation of an enormous lamellipodium and membrane ruffles.
Rho Family- Cdc42
Causes the protrusion of many long filopodia at the cell periphery.
Actin Targeting Drugs- Phalloidin
Binds and stabilizes filaments
Actin Targeting Drugs- Cytochalasin
Caps filament plus ends
Actin Targeting Drugs- Latrunculin
Binds subunits and prevents their polymerizations
Motor Protein for Actin
Myosin II
Microtubule Subunits
The soluble subunit form is the alpha and beta tubulin dimer. 13 of these dimers come together to form the activated microtubule subunit. The soluble subunit is attached to GTP and the activated subunit is attached to GDP. The plus end of the microtubule is dynamic, but the minus end is static because it is stabilized by the MTOC (centrosomes).
Dynamic Instability
Because the microtubule is only being assembled and disassembled from the plus end.
Microtubule targeted drugs- Taxol
Binds and stabilizes microtubules
Microtubule targeted drugs- Colchicine, Colcemid, Vinblastine, Vincristine, Nocodazole
Binds subunits and prevents their polymerization
Microtubules-based astral arrays- MAPS
MAPS serve to bring the microtubules further apart- it binds to the microtubules and provides stabilization and filament spacing.
Microtubules-based astral arrays- Tau
Tau serves to bring microtubules closer together.
Flagella
Wave-like motion and you usually find about 1-2 flagella per cell.
Cilia
Whip-like motion and there are many hundreds in the cell.
Microtubule motor proteins
Kinesins and Dyneins. Kinesins move towards the plus end why the dyneins move towards the negative end.
Kartagener’s Syndrome
Primary ciliary dyskinesia. Leads to infertility, respiration and sinus disorders and flipped organs.
Intermediate Filament subunits
The soluble subunit is an alpha helical region that forms a coil-coil dimer. This dimer forms a staggered tetramer (left and right sides are identical-no polarity, no motor proteins) and the tetramers interact to form a growing filament- which makes this the strongest filament.
