Cytoskeleton Flashcards
3 cytoskeleton filaments
- intermediate filaments
- microtubules
- actin filaments
Actin filament examples
- microvilli
- cytoplasmic contractile bundles
- lamellipodia & filopodia
- cell division contractile ring
Actin filament structure and 2 forms of actin
- 2-stranded helical polymers of actin protein
- 2 forms:
- —-G (globular) - inactive
- —-F (filament) - active
Treadmilling
process of de/polymerisation of actin filaments
ATP-bound actin associated with
polymerisation
ADP-bound actin associated with
depolymerisation
Proteins that stimulate actin behaviour changes
- Rho
- Cdc42
- Rac
Actin & Myosin interaction seen in:
muscle contraction
Cytoskeleton functions (4)
- shape alteration
- internal organisation
- motility
- mechanical interaction with environment
Intermediate filaments basics
- rope-like fibres
- diameter of 10nm
- composed of fibrous protein
- flexible
Intermediate filaments function
- provide tensile strength
- protect against mechanical stress
Intermediate filaments properties
- tough and durable
survive concentrated salt solutions and nonionic detergents - extend across cytoplasm
- anchored to plasma membrane at cell-cell junctions (desmosomes)
- found in nucleus (lamina)
Intermediate filaments structure
alpha-helical monomers with N and C ends coil antiparallel to each other creating dimers which then associate to form tetramers and then lateral associations of 8 tetramers
Intermediate filaments types
- cytoplasmic: keratin, vimentin, neurofilaments
2. nuclear: nuclear lamins
Keratins composition
equal mixture of type 1 (acidic) and type 2 (neutral/basic) keratin chains
Keratin structure
form heterodimers and then fundamental tetrameric subunits held together by disulphide bonds
Keratin disease
epidermolysis bullosa simplex (EBS):
- mutation in K5 or 14 gene
- defective keratins expressed in basal cell layer of epidermis
- skin highly sensitive to mechanical stress
- no cure
Nuclear lamins structure and function
- form a meshwork lining the inner membrane of nuclear envelope
- provide anchorage sites for chromosomes and nuclear pores
- assemble and disassemble during cell division
- degradation controlled by phosphorylation
Nuclear lamins disease
Progeria:
- lamin A mutation
- cell nucleus unstable and mis-formed
- children age prematurely
- no cure
- brain development and function isn’t affected because that’s controlled by lamin C
Microtubule basic properties
- stiff hollow tubules
- radiate from centrosome
- rapid dis/assembly
Microtubule functions
- intracellular transport with help of kinesins and dyenins
- organelle positioning
- power mechanical beat of cilia and flagella
- separate sister chromatids during mitosis
- form mitotic spindle
Kartagener’s syndrome
cilia defect causing respiratory infections and infertility
Microtubule structure
- formed from alpha and beta-tubulin heterodimers
- dimers stack to form wall of cylindrical tube
- 13 parallel protofilaments make tubule
- structural polarity
MTs
- alpha-tubulin at ___ end
- beta-tubulin at ___ end
- alpha: -ve
- beta: +ve
