Cytoskeleton And Cellular Architecture Pt. 1

Front 1

What is the cytoskeleton?

Back 1

It is what defines the size and shape of cells. It also provides support/strength. It is made up of three components:

1. Intermediate filaments

2. Microtubules

3. Actin filaments

Front 2

Where can you find intermediate filaments (IFs)?

Back 2

They underlie the nuclei and crisscross throughout the cell.

Front 3

Of the three types of filaments, which is the strongest and most flexible?

Back 3

Intermediate filaments

Front 4

Why are IFs analogous to a rope?

Back 4

Their strength and flexibility comes from the many thin parallel strands that make them rope like. Unlike a rope, they are also very stretchable.

Front 5

What is the primary building block of IFs? What are its 3 domains?

Back 5

Intermediate filament proteins. They have a head and tail section at the ends. In the middle is the central rod domain, which forms one long linear alpha helix motif.

No high energy nucleotide required for assembly of IF, unlike other cytoskeleton filaments.

Front 6

How are IFs assembled?

Back 6

1. The alpha helical monomers form coiled coil dimers.

2. Two coiled coil dimers form a staggered tetramer. This is the fundamental IF subunit/building block.

3. 8 Tetramers come together to form a Unit Length Filament (ULF)

4. ULFs come together to make intermediate filaments

Front 7

What is the benefit of the coiled coil motif?

Back 7

It is two alpha helices wrapped around each other, which provides strength to the IFs.

Front 8

Why are the tetramer subunits of IFs staggered?

Back 8

The staggered ends allows for further assembly.

Front 9

Do IFs have polarity?

Back 9

No because they are symmetric.

Front 10

What happens to IFs at low levels of stress?

Back 10

They stretch because the alpha helices can stretch. H bonds sever.

Front 11

What happens to IFs at high levels of stress?

Back 11

Dimers slide passed one another in each tetramer.

Front 12

What is the benefit of the interactions between IF dimers, tetramers, and ULFs being relatively weak/unstable?

Back 12

This allows the IFs to deform in order to handle stress.

Front 13

What are the cytoplasmic intermediate filaments? What types of cells are they found in?

Back 13

Desmin filaments: Muscle cells

Keratin filaments: Epithelial cells

Vitamin/vitamin-related filaments: Connective tissue cells, muscle cells, and glial cells

Neurofilaments: Nerve cells

Note: there are approx. 50 different keratins in humans. Different keratins in different tissues.

Front 14

What are the nuclear intermediate filaments?

Back 14

Nuclear lamins: in all animal cells

Front 15

What is the nuclear lamina?

Back 15

A mesh of lamin proteins that support the nuclear envelope (lipids), giving shape and strength to nuclei.

Front 16

What is different about nuclear lamins compared to cytoplasmic IFs?

Back 16

Nuclear lamins completely disassemble during mitosis in each cell cycle, as a result of phosphorylation, then reassemble in interphase as a result of dephosphorylation.

Front 17

What disease is an example caused by a defective nuclear lamin gene?

Back 17

Progeria (children exhibit symptoms of aging).

Front 18

What are desmosomes?

Back 18

Contact points between cells that "lock" them together. They are protein structures that radiate IFs out from both adjacent cells, linking the IF cytoskeleton in neighboring cells. This forms a network extending through many cells.

Cell to cell junctions that anchor IFs to the plasma membrane.

Front 19

What is EBS? What causes it?

Back 19

Epidermolysis bullosa simplex. It is an inherited genetic defect in keratin or keratin-associated proteins.

Symptoms include blistering of skin with mild or no physical trauma, particularly on extremities. Severity depends on which of the 21 skin keratins contains defect as well as position of mutation on the gene.

Mutant protein integrated into keratin IF network renders it susceptible to collapse.

Front 20

What is this an image of?

Back 20

Left is a TEM of normal epidermis. Right is a TEM of an EBS dermis.

Front 21

What is this an image of?

Back 21

Intimidate filament Unit Length Filament

Front 22

What is this an image of?

Back 22

The nuclear lamina mesh.

Front 23

What is this an image of?

Back 23

Florescent microscopy image showing microtubules in green and actin in red.

Front 24

What is plectin?

Back 24

It is an accessory protein that cross links intermediate filaments into bundles and link them to MTs, AFs, and to adhesive structures in the desmosomes. Provides IF stability.