Cytoskeleton

Question 1

Intermediate filament function

Answer 1

Cell shape, Mechanical strength, Flexible

Question 2

Microtubule functions

Answer 2

Cell shape, cell organization, chromosome movement, Rigid and hollow

Question 3

Actin filament function

Answer 3

Cell shape, cell support and migration, cortex and basal lamina

Question 4

Actin Microfilament are made of

Answer 4

Globular actin (g-actin) monomers, polymerize head-to-tail to form actin filaments (F-actin)
Minus side is pointed (slow growth)
Plus side is barbed (rapid growth)

Question 5

Three isoforms of Actin and where

Answer 5

Alpha-only in muscle

Beta and Gamma- almost all non-muscle cells

Question 6

4 diverse functions of Actin

Answer 6

Muscle contraction, Anchoring points with extracellular matrix (stress fibers), Cell surface protrusions (migration/phagocytosis and absorption)
Contractile ring (cytokinesis)

Question 7

Difference in actin bundles and actin networks

Answer 7

Bundles-cross linked linear array, supports microvilli

Networks-cross-linked in orthogonal arrays (3D semisolid gel)

Question 8

Cortical Actin

Answer 8

determines cell shape, locomotion (lammelipodium) and wound healing

Question 9

Types of Actin Bundles

Answer 9

Parallel Bundles- closely spaced, support microvilli, supported by Fimbrin protein
Contractile Bundles- widely spaced, muscle and stress fibers, supported by alpha actinin, binds as dimer

Question 10

Actin binding proteins

Answer 10

Formins-bind actin-ATP add monomers to plus end for linear actin
“Formin a line”
Arp2/3- Bind actin-ATP forms new branched actin
“Branch of aARP2/3
Tropomyosin- bind actin length-wise, stabilizes filament
“My troop is actin stable”

Profilin-Increases ATP-actin concentration

Thymosin-reduces local ATP-actin concentration

Question 11

What are stress fibers?

Answer 11

Large, contractile bundles of actin that provide tension and anchors cell to ECM

Question 12

What is dystrophin?

Answer 12

Binds to Actin, links filaments to plasma membrane proteins of muscle cell
-Loss leads to muscular dystrophy

Question 13

In a RBC, what is cytoskeleton formed from

Answer 13

actin

Question 14

What does spectrin help form?

Answer 14

Binds to actin to form meshwork in cell cortex. Alpha and Beta spectrin chains bind short actin filaments

Question 15

What are microvilli?

Answer 15

Actin-based, finger like protrusions, for increased surface area (intestinal epithelium, phagocytes) anchored to dense terminal web

Question 16

Difference in Myosin I vs Myosin II

Answer 16

Myosin I- in all cells, not involved in contraction, looks like sperm with head that binds actin and hydrolyzes ATP, til binds cargo or memb.
Links actin bundles to membrane
Myosin II-Bipolar filament in muscle contraction, dimerize w 2 chains and globular ATPase

Question 17

Microtubule structure

Answer 17

alpha and beta-tubulin heterodimer (a+head, b-tail), both w single binding site for GTP or GDP

Question 18

Microtubule formation

Answer 18

rapid assembly/disassembly from + end, while - end is tethered to centrosome

Question 19

γ-tubulin

Answer 19

initation site for assembly (-), grows toward periphery (+), nucleates assembly

Question 20

Two forms of Beta tubulin

Answer 20

T and D form (GTP and GDP) T-straight and grows rapidly, then curves to D when GTP is hydrolyzed to GDP which changes conformation, weakens bonds