Zusammenfassung der Ressource
Th1L06 Actin
- part of the cytoskeleton along with IF and MT
Anlagen:
- network of protein filaments that extend
throughout the cell that determine:
- cell shape and polarity
- tissue structure
- adhesion
- cell movement
- intracellular movement (of
vesicles and of chromosomes)
- essential to anchor cells to each other
- essential to anchor cells to anchor extracellular matrix at cell junctions
- structure
- microfilament
- composed of actin-binding proteins
- called F-actin
- filamentous actin or microfilament
- polymers of individual actin
proteins called G-actin (globular
actin)
- polarised double helix
- 13 actin subunits for
every complete turn
- 7nm diameter
- 5% total
protein
- Growth
- (1) requires ATP to be bound to the actin
monomer (G-actin)
- Not very stable over time
- ATP eventually hydrolyses to ADP and will
depolarise and come off at the negative end
- very dyanmic
- monomers can be added and removed from
both ends of the polymer
- G-proteins add more rapidly to (+) end of
the filament
- once incorporated, ATP is hydrolysed
to ADP
- G-protein is removed more rapidly
from the (-) end of the filament
- Function
- provide support
- Maintains the shape of cells
- erythrocytes
- absorption in the gut by forming an adhesion belt
- microvilli in gut
- detect vibration in the cochlea
- In sterocillia
- cells are depolarised or hyperpolarised by
deflections caused by sound; actin filaments keep
them rigid
- Cell migration
- modulate polymerisation dynamics and function
- e.g. myosin, capping proteins, severin, etc.
- required to hold synaptic vesicles close to the presynaptic membrane
- Cell motility
- e.g. migration of neutrophils (WBC) to sites of infection for
phagocytosis
- four events
- (1) cell pushes out protrusions at the front
(leading edge) ○ actin filament
polymerisation provides to force of membrane
protrusion
- (2) ○ protrusions adhere to the
surface on which the cell is moving
through contact junctions; F-actin
connects to the focal adhesions to
provide a contractile force for the
cell
- (3) the rest of the cell pulls against the
anchorage points to drag itself forward
- (4) actin depolymerises at the rear
- Lamellipodia
Anlagen:
- cytoskeletal protein actin projection on the
leading edge of the cell
- extend and withdraw
- generated by rapid growth of actin
filaments at the cell membrane
- the (+) end of actin
filaments are oriented
towards the periphery