Module 3: Lesson 1 Flashcards
(12 cards)
What are actin filaments?
Helical polymers of the protein actin. They are flexible and organized into linear bundles, 2-D networks, and 3-D gels. They are most highly concentrated in the cortex.
What is the function and other characteristics of actin filaments?
They are highly conserved and the most abundant proteins in cells. They are central to cell shape, cell movement, cell division, and phagocytosis. They also interact with actin-binding proteins.
What are actin filaments made of?
They are thin, flexible protein threads with a subunit being an actin monomer called G-actin. It is polar, with a + and - end, and its monomer uses ATP hydrolysis.
What is actin filament treadmilling?
Actin filaments grow rapidly at high concentrations, adding monomers at both ends. At intermediate concentrations, an actin monomer is added to the + end faster than the ATP can be hydrolyzed, growing the + end. If ATP is added faster than the monomer can be added, the filament loses a subunit from the - end.
What are actin toxins?
Cytochalasins (typically D is used), binding to the + end and blocking polymerization. Phalloidin stabilizes actins so they don’t depolymerize.
What are actin-binding proteins?
Proteins that bind to actin monomers in the cytoplasm and regulate when and where actin filaments form and grow.
What do actin-binding proteins form, and what types are there?
They form bundles, sheets, and gel-like 3D networks. There are actin-bundling proteins, cross-linking proteins, severing proteins, filament capping proteins, and side binding proteins.
What are microvilli?
Actin-based protrusions of intestinal epithelial cells held by actin bundles. They increase surface area of the cell for better nutrient absorption.
What are the steps for cell crawling?
Establishment of cell polarity. Actin polymerization at the leading edge protrudes lamellipodium (sheet feet). Formation of adhesive contacts. Translocation of cell body. Retraction of rear, depolymerization of actin networks.
What are actin-related proteins (ARPs)?
Proteins that promote the formation of a web of branched actin filaments in lamellipodia.
What is used as a molecular switch, and what types are there?
GTPases such as Rho, Rac, and Cdc42 use GTP as a molecular switch.
What are myosins and how are they related to actin filaments?
Myosins can transport vesicles, and use actin filaments as tracks. They generate sliding forces to move between different actin filaments. Myosins can bundle and also make myosin filaments.
