The Cytoskeleton

Question 1

Actin Filament Morphology

Answer 1

Two-stranded alpha helical polymers found most concentrated in the cortex just beneath the plasma membrane

Question 2

Microtubule Morphology

Answer 2

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

Question 3

Intermediate Filament Morphology

Answer 3

Ropelike fibers. One type of intermediate filament forms a meshwork called the nuclear lamina.

Question 4

Functions of Actin

Answer 4

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.

Question 5

Functions of Microtubules

Answer 5

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.

Question 6

Functions of Intermediate Filaments

Answer 6

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.

Question 7

Actin Subunits

Answer 7

Actin monomer (soluble) attached to ATP and actin polymer attached to ADP.

Question 8

Actin polymerization

Answer 8

ARP caps the minus end of the actin polymer while CapZ caps the plus end of the polymer.

Question 9

Rho Family- Rho addition

Answer 9

Causes the rapid assembly of the stress fibers.

Question 10

Rho Family- Rac

Answer 10

Causes the formation of an enormous lamellipodium and membrane ruffles.

Question 11

Rho Family- Cdc42

Answer 11

Causes the protrusion of many long filopodia at the cell periphery.

Question 12

Actin Targeting Drugs- Phalloidin

Answer 12

Binds and stabilizes filaments

Question 13

Actin Targeting Drugs- Cytochalasin

Answer 13

Caps filament plus ends

Question 14

Actin Targeting Drugs- Latrunculin

Answer 14

Binds subunits and prevents their polymerizations

Question 15

Motor Protein for Actin

Answer 15

Myosin II

Question 16

Microtubule Subunits

Answer 16

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).

Question 17

Dynamic Instability

Answer 17

Because the microtubule is only being assembled and disassembled from the plus end.

Question 18

Microtubule targeted drugs- Taxol

Answer 18

Binds and stabilizes microtubules

Question 19

Microtubule targeted drugs- Colchicine, Colcemid, Vinblastine, Vincristine, Nocodazole

Answer 19

Binds subunits and prevents their polymerization

Question 20

Microtubules-based astral arrays- MAPS

Answer 20

MAPS serve to bring the microtubules further apart- it binds to the microtubules and provides stabilization and filament spacing.

Question 21

Microtubules-based astral arrays- Tau

Answer 21

Tau serves to bring microtubules closer together.

Question 22

Flagella

Answer 22

Wave-like motion and you usually find about 1-2 flagella per cell.

Question 23

Cilia

Answer 23

Whip-like motion and there are many hundreds in the cell.

Question 24

Microtubule motor proteins

Answer 24

Kinesins and Dyneins. Kinesins move towards the plus end why the dyneins move towards the negative end.

Question 25

Kartagener’s Syndrome

Answer 25

Primary ciliary dyskinesia. Leads to infertility, respiration and sinus disorders and flipped organs.

Question 26

Intermediate Filament subunits

Answer 26

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.