Hitchcock-Degregori - Cytoskeleton I

Question 1

Intermediate Filaments

Answer 1

“Tendons” of the cell. Cytoskeleton + nuclear boundary, protects from mechanical stress, role in signalling. NO MOTORS since no chain polarity

• Structure: 2 a-helices form chain, 2 chains form tetramer, tetramers form higher structures. No polarity since tetramers assemble antiparallel
• include keratins, nuclear lamins, neurofilaments

Question 2

Actin Filaments

Answer 2

Chains of actin monomers. Protein chain has +/- ends, based on FASTER GROWING SIDE, NOT CHARGE. Hydrolyze ATP to form chain, but ATP-actin is more stable, so adds preferentially to + end. Regulated by actin-binding proteins

Question 3

Microtubules

Answer 3

Made of 13 protofilaments each made of tubulin monomers: tubulin = heterodimer of a + b subunits. Like in actin, GTP-bound beta subunit preferentially adds to + end of chain (GTP-bound is T-form, D-form is GDP), T-form dominates in + cap, loss of cap causes degradation like at - end.
-important for vesicle/organelle transport, cilia, centrioles

Question 4

Primary cilia

Answer 4

most cells have 1 cilia, used for sensory, signaling pathways. Unlike motile cilia, no “+2” of “9+2” arrangement,

Question 5

Centrosome

Answer 5

Microtubule organizing center of cell. Microtubules radiate outward, + end at cell periphery

Question 6

MAPS (Microtubule Associated Proteins)

Answer 6

Regulate microtubule activity and assembly, can stabilize ends, cross link or sever the polymer.
ex: Tau is a cross-linking MAP, deficiency can cause Alzheimers

Question 7

Phalloidin & alpha-amanitin

Answer 7

Toxins that can alter microtubule/actin polymerization. Phalloiding binds + stabilizes actin (bad since need to create and degrade), a-amanitin inhibits RNA Pol II

Question 8

Colchicine + Taxol

Answer 8

Microtubule toxins. Colchicine depolymerizes, taxol stabilizes.

Question 9

Cell migration

Answer 9

Uses actin polymerization

ex: neutrophil action chasing bacteria
- Migrate by making more actin + ends: nucleate more, form branches (Arp2/3 does this), sever existing to make more + edges.

Question 10

Arp2/3

Answer 10

Causes side branching on actin filaments to increase + ends for cell migration. Facilitated by Rho-dependent signaling. Rho = GTPase signaling protein
used in wound healing, cell migration, neutrophil activity, etc.

Question 11

Listeria infection mechanism

Answer 11

Listeria has protein similar to Arp2/3 activator, hijacks Arp2/3 to propel itself through cell using actin polymerization

Question 12

Cytoskeleton elements by size

Answer 12

actin