cytoskeliton Flashcards
size and function of microfillaments
5-7nm
Actin Determine cell shape
Allow cell movement
size and function of intermediate filaments
10-12nm
Intermediate filament proteins: large family of proteins
Mechanical strength and structure
size and function of micro-tubules
25 nm in diameter
Organelle and chromosome movement:
Determine position of membrane -bound organelles
Direct transport in the cell
Separate sister chromatids during cell division
actin micro-filaments are used to
1) alow dynamic movement e.g. chemo attraction fillapodia
2) define shape of cell e.g. growth cones fillapodia
3) pinching off of cell in cell division
explain how actin filament polarity contributes to function
G actin can polymerize at both - & + end but polymerizes faster at + end this is used to move actin in a controlled direction
Capping proteins can be used to create unidirectionality in actin explain:
Cap-z
Tropomodulin
Cap-Z blocks + end (normal growth end) limits growth to - end.
Tropomodulin blocks - end where it usually depolymerises stabilizing it for growth.
microtubule composition:
- Polymers of Α and β tubulin forming dimers
- dimers organised in protofilament chains (thermaly unstable)
- multiple protofilaments organised round into 13 subunit tubes which are stable
- can be connected into singlet dublets or triplets
microtubule assembly involes addition of
GTP bound beta tubulin
while GDp bound tubulin is removed
Cytoplasmic kinesin family members walk cargo along microtubules in which diection
towards + end away from centromere
dyenin members walk cargo along microtubules in which diection
towards - end towards centromere
properties of intermidiate fillaments
No intrinsic polarity No nucleotide binding No known motors High stability Unique to metazoans Many different types: -Nuclear lamins -Keratin -Vimentin
keratin structure
Conserved alpha-helical rod domain that forms a coiled -coil motif.
then form protofillaments -pairs of coiled coils (simetric no polarity
these coil together to form microfibrils
Actin cytoskeleton basis of cellular movement in 3 main ways
Chemotaxis = movent response to chemical signal
Muscles
Flagelum
Actin also enables cells to crawl by:
assembling in growth direction and disassembling at other end.
Actin polymerisation drives envagination and phagocytosis by:
by ARP2/3 dependent actin polymerization around nucleation factors on cell surface
there are 3 main classes of myosin explain differences:
class 1 with a singular motor head. Class II and class v are diners class two often conjoining more= less flexibility often used in muscle Class v can walk along an actin filament due to the splay of its motor head enabling e.g. vesicle transport
eukaryotic flagellum consist of:
circular arrangement of micro-tubules with ATP dependent dyenin cross links that bend the flagellum
structure and variation of actin filaments alpha beta and gama
Two stranded helical polymers of G-actin monomers
Alpha form in muscle, beta and gamma in other cells
microtubules convert between growth and shrinkage GTP favours growth GDP favours shrinkage what is this called
dynamic instability
Microtubules often radiate from organising centers (often centrosome) - stable minus end is embedded to prevent breakdown. examples include
Fibroblast: All microtubules head out from MTOC
Neuron axon: microtubule plus end at synapse; minus end in cell body
Transport down long axons; degeneration: starvation of axon terminals
Vesicles transported along microtubules at synapse
(micro-tubules) tubulin mutations:
a-tubulin mutations cause impaired neuronal migration in mice and lissencephaly in humans (a brain development abnormality)
b-tubulin mutations cause cortical malformations in the brain
intermediate filaments- Neurofilament proteins:
light, medium and heavy (NF-L, NF-M, NF-H) NF proteins form cross-links to provide axons with tensile strength The Level of NF gene expression controls axon diameter (structure), hence rate of electrical signal (function)
intermediate filaments- Nuclear lamin proteins
Nuclear lamin proteins A, B and C Form nuclear lamina: meshwork of intermediate filaments lining inside of inner nuclear membrane Determines nuclear shape and provides anchoring point for chromosomes and proteins of nuclear pore complex. Lamin genes are the ancestral intermediate filament. Regulates nuclear reassembly after mitosis
what are the 3 types of cell junction
adherant juctions- hold cells together
occluding junctions- seal the gap
gap junctions- alow transport/comunication
synapses
adherent/anchoring junctions types
Desmosomes: cell to cell
Hemidesmosome: cell to basal lamia
adherins junction connects actin bundeles of two cells
desmosomes connect intermidiate fillaments of once cell to the next
what family of protines hold two desmosomes together
cadherin family
tight occlusion junctions
function:
Examples:
Control permeability between cells paracellular transport
Prevent proteins leaking into the interstitial fluid from capillaries or into bladder from glomerulous.
Barrier to ‘harmful’ luminal contents but allows uptake of nutrients/drugs
Permeability changes dependant on type of tissue small intestine vs blood brain barrier
occlusion junction pathology
Pathologies affect tight junction permeability e.g. Crohn’s disease tight junctions more permeable
gap junction structure/ example
Hexamers of conexin subunit connected end to end
Used for synchronized electrical conductance in brain and cardiac muscle.
