Intermediate Filaments

Question 1

Intermediate filaments are relatively stable structures because of their:

Answer 1

Coiled coil configuration

Question 2

Compared to other filaments, only intermediate filaments have Intrinsic ability to assemble and require not nucleation or assembly proteins. True or false. Why?

Answer 2

True. The assembly and disassembly happens quickly, and it does not require any growth factors. Dimers form
Via the Leucine zipper.

Question 3

What is the leucine zipper?

Answer 3

Made by the dimerization of two alpha helix monomers

Question 4

Intermediate filaments are much more resistant to strain than either actin filaments or microtubules. True or false? Why?

Answer 4

True. They are specialize to withstand tension

Question 5

What does the term “structural” keratin refer to? Give examples

Answer 5

Hard appendages, like
Hair, tongue, and nails.

Question 6

During mitosis, nuclear lamina must rapidly disassemble and deform. How is nuclear lamin disassembly triggered during mitosis?

Answer 6

They are depolymerized by phosphorylation with the mitotic kinase protein CDK 1 during mitosis.

Question 7

One of the earliest events in the assembly of intermediate filaments is the joining of two intermediate filament proteins to form a dimer mi med through a coiled coil. What structural propriety of intermediate filament proteins allows this to occur?

Answer 7

Two alpha long helical rod domains wrap around another alpha helix gaining hydrophobic residues known as the “leucine zipper.”

Question 8

Which two genes constitute most of the intermediate filament genes?

Answer 8

Type 1 (28) and type 2 (26) which are out of the 6 groups based on sequence similarities.

Question 9

Though they are predominantly expressed in mammals, keratins are found in all eukaryotes. True or false

Answer 9

False. They are found in eukaryotic tissues, but not all eukaryotes are found in tissue, and therefore keratin is not present in all eukaryotic cells.

Question 10

The keratins are found in the suprabasal layers of stratified epithelium and are tissue specific. True or false.

Answer 10

True. They are also known as barrier keratins.

Question 11

Are keratins tissue specific?

Answer 11

Yes

Question 12

Keratins and other intermediate proteins are classified into 6 groups based on sequence similarity; keratins make up the majority of type I and type II intermediate filaments. True or false.

Answer 12

True. They make up the majority of type I and type II intermediate filaments.

Question 13

There is a much greater diversity of intermediate filaments than there are actin filaments and microtubules. True or false

Answer 13

True

Question 14

Type III filament proteins form complexes with type I, while type IV form complexes with type II. True or false.

Answer 14

False.

Question 15

Where are type I and type II found?

Answer 15

In epithelial cells

Question 16

Where are type III and type IV found?

Answer 16

In connective tissue, muscle, and nervous system.

Question 17

Compare the similarities and differences between intermediate filaments desmin and vimentin

Answer 17

They both are type III intermediate filaments, but desmin is in muscle cells while vimentin is in loose groups of cells or tissues.

Question 18

The tails of some type IV filaments can be phosphorylated, and this causes the tails to project at a 90 degree angle relative to the filament. This afecta the diameter of the axon. True or false.

Answer 18

True

Question 19

Keratins form attachments to the cell membrane by binding to hemidesmosomes and Desmosomes. True or false

Answer 19

True. They bind to cell-cell matrix junctions Desmosomes and hemidesmosomes

Question 20

What are the similar and original features that distinguishes type V intermediate filaments from the other. 4? Name 3 differences

Answer 20

Type V intermediate filaments have lamins, but they are different from the rest because they are intranuclear, they have unusually long rod domains, and they arise via alternative splicing/complex post translational modifications.

Question 21

Over 50 different types of keratins are expressed in humans, and they are co-expressed as pairs in individual cells. True or false.

Answer 21

True. There are 70 total known human intermediate filament types, to be exact.

Question 22

Name the 6 properties of lamins

Answer 22

-Reinforce nuclear envelope
-Intranuclear
-Form the lamina that lines the nuclear envelope
-The tails have NLSs
-N-lamins are anchored to the nuclear membrane
-Upon phosphorylation by mitotic kinase, lamin filaments depolymerize for disassembly of the nuclear envelope during mitosis.

Question 23

Like type I and type II proteins, type III proteins are abundantly expressed in epithelial cells. True or false.

Answer 23

False. They are expressed in muscle, not epithelial cells.

Question 24

The most common type of intermediate filament associated proteins are ____.

Answer 24

Plakin family

Question 25

What is the role of the plakin family?

Answer 25

They act as linkers in the cytoplasm

Question 26

The presence of keratins in a sheet-like organization is hallmark of epithelial cells. True or false.

Answer 26

True. Sheet tissues lacking keratins are not considered to be epithelial cells, since epithelial cells have keratins.

Question 27

Compared to other filaments, only intermediate filaments require protein contact between heterodimers of intermediate filament proteins. True or false.

Answer 27

False

Question 28

Explain why antibodies to individual filaments are important tools for monitoring cell differentiation and pathology.

Answer 28

They are used as diagnosed markers for cell and tissue differentiation and can be traced through development.

Question 29

What developmental expression trait distinguishes simple keratins from
Barrier keratins?

Answer 29

-Simple = least specialized keratin that highly proliferates in simple epithelium such as intestines and blood vessels
-Barrier = have most complex varied expression and are the least differentiating.

Question 30

What causes the disease epidermolysis simplex (EBS)?

Answer 30

Mutations in K5 or K14

Question 31

The type III protein desmin is expressed in a wide range of tissue types, while vimentin is expressed primarily in muscle cells. Both proteins co-express with GFAP in the nucleus. True or false.

Answer 31

False. Type III is expressed in muscle cells while type IV is expressed in a wider range of tissue types.

Question 32

Compared to other filaments, only intermediate filaments do not require ATP for growth. True or false.

Answer 32

True. Instead of ATP, they depend on the leucine zipper and phosphorylation.

Question 33

Keratins are expressed in and around specialized structures such as hair and nails. True or false.

Answer 33

True