Topic 6: Actin and Intermediate Filaments Flashcards
Three general areas of cytoskeleton within the cytoplasm?
1) Cortical cytoplasm - just beneath the plasma membrane helps give shape to the cell. Dominated by an interconnected meshwork of microfilaments. Large membranous organelles and other bulky structures
2) subcortical cytoplasm and endoplasm - major organelles reside in this region and are spatially organized and often attached to cytoskeleton elements
3) Nuclear cytoskeleton- Important in mitosis allows the nucleus to maintain and change its shape. Nuclear lamins give the nucleus form
Where in the cell would you most likely find actin?
Cytoskeleton. Maintains cell shape resisting pull. Specifically, the nuclear cytoskeleton.
What characteristics of G actin allow it to form F actin?
G actin has a + end and F actin only has a negative end so can only bind to positive end.
What favors G actin to polymerize?
G actin bound to ATP favorably associates with the positive end of microfilament
What favors G actin to dissociate from the microfilament?
Binding G actin will eventually lead to hydrolysis of ATP to ADP, presence of ADP promotes depolymerization
What is nucleation?
The formation of trimers followed by more rapid growth
Explain treadmilling in actin Filaments
individual pieces of actin are shuffled to move the entire cell around in an environment
Proflin
Stimulate ADP exchange for ATP
Formin
catalyze nucleation and extension of microfilament
Arp 2/3 complex
initiates the formation of branches
capping proteins and trypomyosin
stablize filaments
cross linking proteins
cross link filaments into bundles and networks
cofiln
sever acting filaments
What are microville and stereocilia
microvilli: are fingerlike extensions abundant on cells involved in absorption, formed by actin bundles
Stereocilia: Finger like extensions involved with detecting extracellular changes
What are Rho proteins
couples to receptors and respond to environmentally cues by activating actin-binding proteins. Stimulates actin remodeling and cell movement.
Main functions of intermediate filaments?
Important for scalfolding. More resistant to stretch and bending forces than microtubules but less resistant to actin. Support plasma membrane. Position of nucleus and certain organelles.
Process of intermediate filament polymerization, how leads to final filament structure?
- two polypeptides will dimerize connected by central rod domain
- Two dimers combine to form a tetramer
- tetramers will stack on one another end to end to form protofilament
- 8 protofilaments will combine twisting around each other to form a rope like structure called a filament
3 locations where to find intermediate filaments
hair, scales, and fingernails
What are hemidesmosomes
junction between cell and connective matrix (cell to substratum)
What are demosomes?
Junctions between cells (cells to cells)
