Cell Bio- Cytoskeleton

Front 1

What is cytoskeleton:

Back 1

Dynamic system of structures formed by protein filaments

Front 2

Function of cytoskeleton:

Back 2

1. Intrinsic support of the cell (skeleton of the cell) including formation of cell shape
2. Movement of the cell (intracellular movements, and also movement of the whole cell)
3. Cell signaling

Front 3

What enables fast rearrangement of cytoskeletal structures?

Back 3

A dynamic balance between monomeric units and polymeric filaments of the cytoskeleton

Front 4

Types of cytoskeleton filaments:

Back 4

1. Microtubules
2. Intermediate filaments
3. Microfilaments (actin filaments)

Front 5

Microtubules:

Back 5

Monomers of alpha and beta tubulin form dimers. Filament diameter of 25nm

Front 6

Intermediate filaments:

Back 6

Consists of monomers of lamins (lamin A, B, C) (nuclear lamina). Keratins (epithelial cells and their derivatives, hair, nails). Vimentin- type proteins (cells of mesenchymal origin), desmin (muscles) and proteins of neurofilaments. FIlament diameter about 10nm.

Front 7

Microfilaments:

Back 7

Monomer actin. Filament diameter about 7nm.

Front 8

Drugs affecting cytoskeletal filaments:

Back 8

1. Colchicine (stabilizes free tubulin and thus prevents its polymerization)
2. Vinblastin, vincristin (it stabilizes free tubulin and thus prevents its polymerization)
3. Taxol (it stabilizes polymerized tubulin, e.g. microtubules)
4. Latrunculin (it binds to free actin and thus prevents its polymerization)
5. Phalloidin (it stabilizes polymerized actin e.g. microfilaments)

Front 9

Structure of microtubules:

Back 9

- Polymers of dimers of alpha and beta tubulin form protofilaments.
- Microtubules are long hollow tubes made up from 13 parallel protofilaments.
- Binding GTP is indispensable for polymerization.
- Bound GTP--> growth of microtubule
- Bound GDP--> shrinkage of microtubule
- Microtubules are by their "- end" attached to MTOC (microtubule organizing center). Dynamic instability

Front 10

Function of microtubules:

Back 10

1. Mitotic spindle: it realizes chromosome separation during mitosis. There are centromeres (each chromosome contains pairs of centrioles) on the poles of mitotic spindle, where microtubules are anchored by their minus- end.
2. Flagella and cilia: enables movement of the cell and movement of particles surrounding the cell. Flagella and cilia are formed by 9 parallel doublets of microtubules around two central microtubules. Microtubules of flagella and cilia are anchored by their minus end to a basal body. Bound motor protein dynein enables the movement of flagella and cilia
3. Tracks for the movement of organelles within the cell: motor proteins dynein and kinesin enables the movement. Dynenin mover to the - end of the microtubule and kinesin moves to the + end of the microtubule.

Front 11

Structure of intermediate filaments:

Back 11

- Monomers form parallel dimers. (C- terminus to C- terminus and N- terminus to N- terminus)
- Two dimers form antiparallel tetramer (C- termini to N- termini and N- termini to C- termini)
- Polymers of these tetramers form a fiber
- Intermediate filaments are made up from 8 of these fibers twisted in a rope- like structure
Monomeric molecules of proteins of intermediate filaments have a central alpa- helical domain and two terminal (C-terminus and N- terminus) globular domains

Front 12

Function of intermediate filaments:

Back 12

1. Nuclear lamina
2. Intermediate filaments in the cytoplasm

Front 13

Nuclear lamina:

Back 13

- Intermediate filaments of nuclear lamina are made up of proteins lamins (not the same as laminin which is in the extracellular matrix).
- Nuclear lamina is attached to the inner face of the nuclear envelope where it forms mesh- like structures. It controls the integrity of nuclear envelope by phosphorylation (disintegration) and dephosphorylation (intergration)

Front 14

Intermediate filaments in cytoplasm:

Back 14

- Have high mechanical resistance and support mechanical stability of the cells
- They form the "real" skeleton of cells
- Keratins: are in epithelial cells, hair, nails and feathers
- Epidermolysis bullosa simplex (mutation in keratin genes)
- Vimentine: in connective tissue cells.
- Desmin: in muscle cells.
- Proteins of neurofilaments: they are in neurons, mainly in axons.

Front 15

Structure of microfilaments:

Back 15

- Polymers of globular molecules of actin
- Have a double helical structure
- Binding of ATP is indispensable for polymerization
- Bound ATP: growth (+end)
- Bound ADP: shrinkage (-end)
- Dynamic instability

Front 16

Function of microfilaments:

Back 16

1. Microvilli: small hair like projections of cytoplasm on the cell surface which are supported by microfilaments
2. Cell cortex: made of actin microfilaments. Cell cortex is attached to the inner face of the plasma membrane where microfilaments form mesh- like structure. It function as a mechanical support of the plasma membrane
3. Contractile ring: a ring of microfilaments which realize cell division
4. Lamelliopodia, filopodia, pseudopodia: sheetlike or fingerlike protrusions of the plasma membrane which contain microfilaments. They are involved in amoeboid locomotion of the cell
5. Contractile bundles: of microfilaments in the cytoplasm form the cell shape. They function as "muscles" of the cell

Front 17

Myosins:

Back 17

Myosin I: all cell types
Myosin II: muscles