Cytoskeleton Flashcards
What is the cytoskeleton?
Network of protein filaments throughout cytoplasm
What are the functions of the cytoskeleton?
Mitosis + Cytokinesis Traffic Support Cell shape Muscle contraction
What are the 3 types of cytoskeleton filament?
Intermediate filaments
Microtubules
Actin filaments
What to intermediate filaments do?
Where are they abundant?
Provide tensile strength
Cells subject to mechanical stress e.g. muscle cells
What are the 3 main classes of intermediate filaments?
Keratin filaments
- epithelial cells
Vimentin filaments
- connective tissue cells, muscle cells + supporting cells
Neurofilaments
- nerve cells
What are nuclear lamins?
Intermediate filaments found just under nucleus membrane
What are intermediate filaments made of?
Monomers with a central rod domain + globular region at either end
Describe the construction of an intermediate filament
- Monomers dimerise
- 2 dimers line up to form a staggered tetramer
(N terminus near C terminus of other dimer) - Tetramers pack together end to end
- 8 tetramers twisted into a rope
How do keratins connect neighbouring cells?
Indirectly connected to filaments of other cells through desmosomes (cell-cell junctions)
How do keratins indirectly connect cells via desmosomes?
Cadherins span the 2 membranes
-> bind the 2 cells together
Give an example of an intermediate filament disorder
Epidermolysis bullosa simplex
= keratin cannot form normal filaments in the epidermis
-> skin v susceptible to injury
What is the difference between lamins + laminins?
Lamins = cytoskeleton proteins
Laminins = ECM proteins
Why are intermediate filaments v stable, strong + durable?
Extensive protein-protein contacts
Describe actin filaments
In all eukaryotic cells
Made up of globular monomers that associate head to tail
Unstable w/out associated proteins
When do F-actin filaments form?
Spontaneously from G-actin above the critical conc
In the presence of ATP, Mg + K
Describe the polymerisation of actin
- Actin monotoners in cytosol carry ATP
- ATP hydrolysed -> ADP after monomers assemble into filament
- ADP replaced with ATP when actin disassembles from filament
Which proteins bind to actin to modify its properties?
Monomer binding proteins Nucleating " Cross-linking " Capping " Bundling " Motor "
What are 2 drugs that act on the actin cytoskeleton?
Cytochalasin D
- binds to +ve end of F-actin
- > prevents further addition of G-actin
Phalloidin binds F-actin + prevents actin filaments from depolymerising
What are the 4 functions of actin?
> Mechanical strength + cell shape
Cell crawling
Muscle contraction
Organelle movement
What is cortical actin?
Actin filaments concentrated in a layer in the cortex
- linked into a meshwork by actin binding proteins
What is cell crawling?
Filopodia or lammelipodia extend a region of plasma membrane
(driven by actin cytoskeleton rearrangement)
Integrins adhere to ECM
Cells use internal contractions to pull itself forward
Which family of proteins do actin dependent motor proteins belong to?
Myosin family
How does mysosin move along actin filaments?
Myosin binds + hydrolyses ATP
-> provides energy
= moves from - to + end
Describe microtubules
Long, hollow cylinders made of tubulin
Most rigid + straight type of filament
