Cytoskeleton

Question 1

what are the three main actin filament nucleators?

Answer 1

Arp2/3 (branched structures & push lamellipodia forward)

Formins (unbranched contractile rings & filopodia)

WH2 domains (bind G-actin)

Question 2

what is the role of thymosin B4?

Answer 2

binds unpolymerised g - actin on cytoplasm

blocks uncontrolled polymerisation.

Question 3

how do cofilin & gelsolin differ?

Answer 3

cofilin bunds ADP actin filaments, accelerating disassembly of older filaments

gelsolin severs filaments & bonds barbed end (preventing assembly).

Question 4

How can the speed of actin polymerization be increased?

Answer 4

profilin binds polyprolines in formins & Ena/VASP

gives ATP-G-Actin for barbed end.

Question 5

outline the stricture of a centrosome.

Answer 5

pair of centrioles embedded in a protein matrix with 100s of ring shaped gamma tubulin structures.

Question 6

Give examples of two destabilising microtubule binding proteins.

Answer 6

Stathmin - binds two heterodimers

Katanin - severs microtubules.

Question 7

how do taxol and colchicine differ?

Answer 7

taxol binds mts, preventing subunit loss (continued growth –> mitosis arrest)

colchicine binds dimers, preventing polymerisation (mitotic spindle disappears).

Question 8

describe the axoneme.

Answer 8

forms core of cilia and flagella
9 doublet microtubules arranged around a pair of single mts.
at regular positions, proteins cross-link MTs

Question 9

how do cells crawl?

Answer 9

barbed end faces PM

actin anchored to ECM through integrins

anchored filaments elongate –> lamellipodia

myosin motors retract rear of cell pulling on antiparallel F-actin.

Question 10

relate the structure of myosin & it’s relationship to actin.

Answer 10

2 heavy chains with head which binds actin & hydrolyses atp to move along

2 light chains are tails which vary depending on cargo.