cytoskeleton; intermediate filaments

Question 1

where are they found

Answer 1

• nearly all mammal cells
• absent from plants and fungi

Question 2

structure and function

Answer 2

rope like network of filaments
principal function is to maintain cell structure and tensile strength

Question 3

IF differ from AF and MT

Answer 3

• no defined polarity
• no associated motor proteins
• dont bind to nucleotides; ATP, GTP
• very stable in comparison

Question 4

4 types of IFs

Answer 4

• cytoplasmic; keratins, vimentin and vimentin related, neurofilaments
• nuclear; nuclear lamins

Question 5

function of IF in cytoplasm

Answer 5

• tensile strength; withstand mechanical stress
• structural support; creating deformable 3D structure, reinforcing cell shape and fix organelle localisations

Question 6

stratified squamous epithelium

Answer 6

• stem cells interior
• dead cells at outmost surface
• keratin remains; hard, waterproof, resists abrasions
• makes up hair, nails, skin, feathers

Question 7

what do keratins do?

Answer 7

form strong network indirectly linked to neighbouring cells

Question 8

hemidesmosomes

Answer 8

mediate cell-matrix adhesion between epithelial cells and basal lamina
- integrins a6b4 binds to proteins in plaques to lamin in ECM

Question 9

what does disruption of keratin networks cause

Answer 9

blisters

Question 10

vimentin required for what

Answer 10

trans-epithelial migration

Question 11

endothelial migration

Answer 11

WBCs leave blood stream to combat infection
- process impaired in mutant mice

Question 12

desmin filaments function

Answer 12

maintain muscle structural integrity
mutant mice=misaligned muscle fibres
mutations in humans = muscle disorders

Question 13

desmin filaments structure

Answer 13

tethered to Z disk like sarcomere

Question 14

neurofilaments

Answer 14

have side arm projections from core filaments
fill and pack cytoplasm with neurons

Question 15

charcot-marie-tooth disease

Answer 15

peripheral nervous system degenerates

Question 16

functions of IF in the nucleus

Answer 16

• in all nucleated euk cells
• form mesh rather than rope like structure
• line in inner face of nuclear envelope and give ; strength, provide attachment for chromatin

Question 17

IF and cell division

Answer 17

reform at each division
- very different from cytoplasmic IFs
- controlled by post-trans mods.
- form basket like structure on inner side of nuclear membrane that protects structure
- disassemble when cells enter mitosis

Question 18

IFP; IF binding proteins

Answer 18

• mainly linkers of IF structures

Question 19

stabilise and reinforce IF into 3D networks

Answer 19

• fillagrin; binds keratin into bundles
  -synamin and plectin; bind vimentin and desmin
• plakins; contact between desmosomes + epthelial cells