cytoskeleton

Question 1

Actin monomers and filaments

Answer 1

-globular, bind ATP and Mg2+
-monomers assembles into double strand helix, requires ATP hydrolysis
-polar: +and - end
“tredmilling”
-assembly regulated by thymosins and profilms

Question 2

ARP complex

Answer 2

• actin related protein
• makes lamellipodia
• helps assembly of branched actin at leading edge of an extending cell membrane
• disassembly away from edge to regenerate actin monomers
• capping limits growth
• would stop cytokinesis if inhibited

actin associated with stabilizing membrane are found in microvilli, stress fibers, lamellipodia and contractile rings
-contraction and extension of PM forms filopodia and lamellipodia

Question 3

Myosin I and II in non-muscle

Answer 3

myosin I - single headed. dontf form filaments. walks along actin towards + end
myosin II - forms bipolar filament. interacts with two actin filaments: one on each side that are moving in opposite directions

-regulation of actin-myosin non-muscle contraction is based on phosphorylation of myosin-associated light chains. Ca2+ causes phosphorylation. too slow for skeletal muscle

Question 4

contraction in skeletal muscle

Answer 4

• actin/thin filament regulated
• Ca binds troponin. this changes conformation of tropomyosin - opening the myosin binding site on actin and allowing myosin to bind

Question 5

intermediate filament structure

Answer 5

• monomeric rods coil into dimers, then tetramer, then large bundle
• globular ends
• no polarity, thus not for motility

Question 6

types of intermediate filaments

Answer 6

1. keratin - hair, skin, nails, epithelial cells
   - for strength
   - need as a barrier and for skin
   - epithelial cancer detection. skin blisters if deficient
2. vimentin, desmin, Glial - in connective tissues, muscles and neurons. form desmosomes for cell-cell attach
3. neurofilaments - in neurons. 3 subunits bind for tensile strength
4. nuclear lamins - forms nuclear lamina. mutations cause laminopathies like Progeria.

Question 7

microtubule structure

Answer 7

• alpha and beta tubulin are each globular proteins bound to GTP
• form A,B dimer. GTP locked on A and hydrolyzes on B
• MT formation is head to tail. requires GTP hydrolysis and certin subunit concentration
• is polar
• drugs can block MT assembly (which can stop cell division) and treat gout as well as cancer

Question 8

microtubule dynamic instability

Answer 8

• when all of GTP is hydrolyzed, + end disassembles
• can continuously disassemble and reassemble. change distribution and find areas that need MTs
• distribution also regulated by MTOCs - get -end of MT to bind centrosomes
• MTs are stable once they are acetylated

Question 9

Kinesins and Dyneins

Answer 9

-motor proteins in MTs
dynein -2 headed in cytoplasm (1 or 3 heads in cilia/flagella)
-move toward - end

kinesin - 2 headed ATPases
+ end motility

• aid in chromosome segregation and organelle transportand organelle placement in cell
• disruption leads to neurodegenerative disease

Question 10

cilia/flagella sliding doublet

Answer 10

• 9 doublets form a cylinder with 1 singlet in middle if motor protein
• dynein holds two doublets together
• MT sliding causes a bend(with dynein) and a wave of propogation
  (vs. muscle cell - sliding is linear, not a wave)

Question 11

cilia functions

Answer 11

1. motile
   -airways, fallopian tubes, brain ventricles to move fluid
   kartageners syndrome/primary diskenesia - lack motility cilia. get infertile sperm, respiratory disease and left/right assymetry
2. sensory (lack singlet central MT and dynein arms)
   -mechanoreceptors in kidney and cartilage
   -sensing during embrygenesis
   -in nose, ear, eyes