cytoskeleton Flashcards
How many types of polymers are there?
→3 types
what are the types of polymers called?
→microfilaments / actin,
→microtubules
→intermediate filaments
what are microtubules for?
→ organelle positioning
→ intracellular transport
what are intermediate filaments for?
→ mechanical strength
what are actin filaments for?
→ cell shape
→ organelle shape
→ cell migration
give two properties of the polymers that make up the cytoskeleton
→ monomers are very abundant
→ not covalently linkes
what is the structure of actin filaments and what are the isoforms?
→Twisted chain of units (monomers) of the protein actin (G-actin, aprox.43 KDa). This chain constitutes the filamentous form (F-actin).
→Thinnest class of the cytoskeleton filaments (7 nm)
→Presents structural polarity
→Associated with a large number of actin-binding proteins (ABP)
→There are 3 isoforms of G-actin with different isoelectric points :
α-actin found mainly in muscle cells
β-actin and γ-actin in non-muscle cells
how can actin polymerize?
→Actin filaments (F-actin) can grow by addition of actin monomers (G-actin) at either end.
what does the length of the polymerized actin filament depend on?
→Concentration of G-actin.
→Presence of Actin Binding proteins (ABPs)
what are G actin levels controlled by?
2 actin binding proteins
what are the two actin binding proteins that regulate G actin and what do they do?
→Profilin: facilitates actin polymerization.
→Thymosin β4: prevents the addition of actin monomers to F-actin.
What are the two actin binding proteins that bind to F actin?
Actin bundling proteins
→ keep F-actin in parallel bundles (as in the microvilli observed in epithelial cells)
Cross linking proteins
→ keep actin in gel like mesh work under membrane
what do F actin severing proteins do?
→break F-actin into smaller filaments
what do motor proteins do?
→transport of vesicles and/or organelles along actin filaments.
what proteins break actin apart?
→F actin severing proteins