14.5 Intermediate Filaments

Question 1

protein filaments that have diameters intermediate between actin filaments and microtubules

Answer 1

intermediate filaments

Question 2

intermediate filaments aren’t involved in cell movement, but they ()

Answer 2

provide mechanical strength and a scaffold for localization of cell processes

Question 3

intermediate filaments are usually found in ()

Answer 3

higher-order eukaryotes

Question 4

types I and II of intermediate filaments are ()

Answer 4

keratins

Question 5

the type of keratins found in hair, nails, and horns

Answer 5

hard keratins

Question 6

type of keratin found in cytoplasm of epithelial cells

Answer 6

soft keratin

Question 7

examples of type III intermediate filaments

Answer 7

1. vimentin - found in fibroblasts, smooth muscle, and WBCs
2. desmin - expressed in muscle cells and connects Z discs of sarcomeres

Question 8

type IV intermediate filaments include:

Answer 8

1. neurofilament (NF) proteins - major intermediate filaments of neurons
2. nestin - expressed during embryonic development in several types of stem cells

Question 9

type V IFs are the (), which are nuclear components rather than parts of the cytoskeleton

Answer 9

nuclear lamins

Question 10

all IFs have a central () flanked by N- and C-terminal domains (vary among IF proteins in size)

Answer 10

⍺-helical rod domain (approx 310-350 amino acids)

Question 11

overview of intermediate filament structure

Answer 11

polypeptide chains → dimers → tetramers → protofilaments → filaments

Question 12

dimers of cytoskeletal IFs associate in a () to form tetramers

Answer 12

staggered, antiparallel fashion

Question 13

tetramers have equivalent ends → IFs are ()

Answer 13

apolar

Question 14

approx. () wind around each other in a rope-like structure to form intermediate filaments

Answer 14

8 protofilaments

Question 15

in epithelial cells, keratin filaments are tightly anchored to the plasma membrane at 2 areas of specialized cell contacts:

Answer 15

1. desmosomes
2. hemidesmosomes

Question 16

junctions between adjacent epithelial cells

Answer 16

desmosomes

Question 17

in desmosomes, cell-cell contacts are mediated by transmembrane proteins related to ()

Answer 17

cadherins

Question 18

stable association between the cadherin-like proteins (1) and (2) is critical for tight interaction between cells

Answer 18

1. desmoglein
2. desmocollin

Question 19

on the cytoplasmic side of desmosomes, they are associated with a characteristic dense plaque of intracellular proteins, which serve as ()

Answer 19

attachment sites of keratin filaments

Question 20

(keratin) intermediate filament attachments are mediated by which 3 proteins?

Answer 20

1. desmoplakin
2. plakoglobin
3. plakophilin

Question 21

desmoplakin and plectin are part of of the () family, which bind IFs and link them to other cellular structures

Answer 21

plakins

Question 22

junctions between epithelial cells and underlying connective tissue (i.e. substratum)

Answer 22

hemidesmosomes

Question 23

in hemidesmosomes, intermediate filaments are bound to ()

Answer 23

plectins

Question 24

in hemidesmosomes, () link the extracellular matrix and plectin

Answer 24

integrins

Question 25

() regulate hemidesmosome assembly and stability

Answer 25

BP180 and BP230

Question 26

The role of (keratin) intermediate filaments in healthy skin was shown in studies using transgenic mice with a ()

Answer 26

keratin mutation

Question 27

what was found in transgenic mice with keratin mutations?

Answer 27

mutation disrupted formation of a normal keratin cytoskeleton, resulting in severe skin abnormalities