Class 20 - Intermediate Filaments and Septins (PRETTY GOOD)

Question 1

Intermediate filaments

Answer 1

NOT found in all eukaryotic cells. Very diverse. All have central alpha-helical domain and coil-coiled structure.

Tetrameric subunits made of two dimers pointing opposite ways - nonpolar.

Stretchy and bendy but hard to break.

Question 2

Desmosomes

Answer 2

When keratin filaments impart mechanical strength to epithelial tissues by anchoring intermediate filaments at sites of cell-cell contact.

Question 3

Hemidesmosomes

Answer 3

When keratin filaments impart mechanical strength to epithelial tissues by anchoring intermediate filaments at sites of cell-matrix contact.

Question 4

Plakins

Answer 4

Intermediate filaments which link network to rest of cytoskeleton. Can interact with protein complexes (SUN and KASH proteins) that connect cytoskeleton to nuclear interior.

Question 5

Nuclear lamins

Answer 5

Component of meshwork called nuclear lamina lining inner membrane of nuclear envelope

provide anchorage sites for chromosomes and nuclear pores and structural support for nuclear envelope.

Question 6

Keratins

Answer 6

Most diverse intermediate filament family. Provide strength to epithelial tissues. Co-polymerize into single network.

Mutations cause blistering diseases.

Question 7

Epidermolysis bullosa simplex

Answer 7

Keratin defect which causes skin blisters in response to slight mechanical stress, which ruptures basal cells.

Question 8

Filaggrin

Answer 8

An accessory protein which bundles keratin filaments of epidermis to give the outmost layers of the skin toughness.

Mutations in filaggrin predispose people to dry skin diseases.

Question 9

Neurofilaments

Answer 9

Family of intermediate filaments found along axons of vertebrate neurons. Controls axon diameter and how fast electrical signals travel down axon, also providing strength.

ALS - Abnormal assembly of neurofilaments which interfere with axon transport. Lead to muscle weakness and atrophy.

Question 10

Desmin

Answer 10

Type of intermediate filament expressed in cardiac, skeletal, and smooth muscle. Forms scaffold around Z disc of sarcomere, stabilizing muscle fibers.

Question 11

A-type lamins

Answer 11

Scaffolds for proteins that control cellular processes including transcription, chromatin organization, and signal transduction.

Question 12

Plectin

Answer 12

Type of plakin which bundles intermediate filaments and links them with microtubules, actin filament bundles, and filaments of motor protein myosin II. Also helps attach intermediate filaments to adhesive structures at plasma membrane.

Mutation - causes combination of Epidermolysis bullosa, muscular dystrophy, and neurodegenration

Question 13

SUN and KASH proteins

Answer 13

INTERMEDIATE FILAMENT linker proteins.

SUN - Inner nuclear membrane, bind to nuclear lamina or chromosomes.

KASH - Outer nuclear membrane, bind to actin filaments directly or microtubules/intermediate filaments indirectly.

Bind to each other with lumen of nuclear envelope, forming bridge.

Question 14

Septins

Answer 14

GTP-binding proteins. additional filament system in all eukaryotes but plants.

Act as scaffolds to compartmentalize membranes into domains or recruit action and microtubule cytoskeletons.

In budding yeast, block movement of proteins around neck to concentrate growth to the bud.

In animal cells, function in cell division, migration, vesicle trafficking, and primary cilia.