Bio 11/18

In vitro: when there's a high concentration of tubulin dimers, microtubules grow…

at both ends

In vivo: what end of the microtubule must be stabilized?

the minus end (alpha)

In vivo: where are microtubules stabilized?

at microtubule organizing centers (MTOC)

What is the structure of an MTOC?

an arrangement of nine, triplet microtubules

What is microtubule catastrophe? How does it happen?

tubulin dimers have GTP bonds. During microtubule growth, GTP is hydrolyzed to GDP. At + end of microtubule, a GTP "cap," stabilizing it. If end is GDP, then everything splits and falls apart.

What is this microtubule growing and shrinking called?

Dynamic Instability

What are two drugs that affect microtubules and how?

Nocadazole: prevents addition of dimers at + end, causing microtubules to fall apart. Taxol: stabilizes microtubules, locking cytoskeleton in place, one of the first anticancer drugs, prevents cell division.

What is the structure of an actin filament?

thin, two intertwined actin polymers. Also has polarity (+ end/barbed end and - end/pointy end)

How are the ends of actin characterized? Which side grows?

plus + end has ATP and grows, - end has ADP and preferentially depolymerizes

Assembly of an actin filament is energetically….

highly favorable! (ATP -> ADP)

What is the structure of actin filaments in a cell?

highly branched

Actin branching is mediated by…?

Arp 2/3 complex. Always anchors minus ends, new filaments always at 70 deg

Drugs that affect actin cytoskeleton?

cytochalasin: depolymerizes actin. Phalloidin: stabilizes actin filaments

Lysteria Monocytogenes take advantage of actin cytoskeleton how?

has a protein called ActA that binds to the Arp2/3 complex which in turn assembles actin, pushing the bacteria along.

motor protein that walks towards the periphery?

Kinesin, + directed

motor protein that walks towards the center?

Dyein, - directed

motor proteins require how much energy?

1 ATP per step