Intermediate Filaments Flashcards
Intermediate filaments are relatively stable structures because of their:
Coiled coil configuration
Compared to other filaments, only intermediate filaments have Intrinsic ability to assemble and require not nucleation or assembly proteins. True or false. Why?
True. The assembly and disassembly happens quickly, and it does not require any growth factors. Dimers form
Via the Leucine zipper.
What is the leucine zipper?
Made by the dimerization of two alpha helix monomers
Intermediate filaments are much more resistant to strain than either actin filaments or microtubules. True or false? Why?
True. They are specialize to withstand tension
What does the term “structural” keratin refer to? Give examples
Hard appendages, like
Hair, tongue, and nails.
During mitosis, nuclear lamina must rapidly disassemble and deform. How is nuclear lamin disassembly triggered during mitosis?
They are depolymerized by phosphorylation with the mitotic kinase protein CDK 1 during mitosis.
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?
Two alpha long helical rod domains wrap around another alpha helix gaining hydrophobic residues known as the “leucine zipper.”
Which two genes constitute most of the intermediate filament genes?
Type 1 (28) and type 2 (26) which are out of the 6 groups based on sequence similarities.
Though they are predominantly expressed in mammals, keratins are found in all eukaryotes. True or false
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.
The keratins are found in the suprabasal layers of stratified epithelium and are tissue specific. True or false.
True. They are also known as barrier keratins.
Are keratins tissue specific?
Yes
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.
True. They make up the majority of type I and type II intermediate filaments.
There is a much greater diversity of intermediate filaments than there are actin filaments and microtubules. True or false
True
Type III filament proteins form complexes with type I, while type IV form complexes with type II. True or false.
False.
Where are type I and type II found?
In epithelial cells
Where are type III and type IV found?
In connective tissue, muscle, and nervous system.
Compare the similarities and differences between intermediate filaments desmin and vimentin
They both are type III intermediate filaments, but desmin is in muscle cells while vimentin is in loose groups of cells or tissues.
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.
True
Keratins form attachments to the cell membrane by binding to hemidesmosomes and Desmosomes. True or false
True. They bind to cell-cell matrix junctions Desmosomes and hemidesmosomes
What are the similar and original features that distinguishes type V intermediate filaments from the other. 4? Name 3 differences
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.
Over 50 different types of keratins are expressed in humans, and they are co-expressed as pairs in individual cells. True or false.
True. There are 70 total known human intermediate filament types, to be exact.
Name the 6 properties of lamins
-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.
Like type I and type II proteins, type III proteins are abundantly expressed in epithelial cells. True or false.
False. They are expressed in muscle, not epithelial cells.
The most common type of intermediate filament associated proteins are ____.
Plakin family
What is the role of the plakin family?
They act as linkers in the cytoplasm
The presence of keratins in a sheet-like organization is hallmark of epithelial cells. True or false.
True. Sheet tissues lacking keratins are not considered to be epithelial cells, since epithelial cells have keratins.
Compared to other filaments, only intermediate filaments require protein contact between heterodimers of intermediate filament proteins. True or false.
False
Explain why antibodies to individual filaments are important tools for monitoring cell differentiation and pathology.
They are used as diagnosed markers for cell and tissue differentiation and can be traced through development.
What developmental expression trait distinguishes simple keratins from
Barrier keratins?
-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.
What causes the disease epidermolysis simplex (EBS)?
Mutations in K5 or K14
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.
False. Type III is expressed in muscle cells while type IV is expressed in a wider range of tissue types.
Compared to other filaments, only intermediate filaments do not require ATP for growth. True or false.
True. Instead of ATP, they depend on the leucine zipper and phosphorylation.
Keratins are expressed in and around specialized structures such as hair and nails. True or false.
True
