CH 17

Flashcards about Cell Organization and Movement I: Microfilaments

Actin

Highly conserved and abundant eukaryotic cell protein that assembles into diverse structures of actin filaments for different functions.

G-actin

Monomeric actin that reversibly assembles into polarized F-actin filaments.

F-actin

Polarized actin filaments composed of two protofilaments, in which the actin subunits are all oriented in the same direction. Protofilaments are wound around each other to form a helix with the actin nucleotide-binding site exposed on the (−) end of each protofilament.

Profilin

Binds to ADP–G-actin, opening the cleft and catalyzing the exchange of ADP for ATP. Sterically blocks ATP–G- actin assembly on the filament (–) end but allows the unblocked G-actin monomer end to assemble onto the filament (+) end.

Cofilin

Fragments ADP-actin filament regions, enhancing overall depolymerization by making more filament (–) ends.

Thymosin-β4

Provides a buffered reservoir of ATP–G-actin for polymerization by sequestering G-actin at high concentration and releasing G-actin at low concentration to polymerize.

Capping proteins

Block assembly and disassembly at filament ends.

Formins

Actin-nucleating proteins regulated by signaling pathways that nucleate actin assembly.

Arp2/3 complex

Moves pathogenic bacteria and endocytic vesicles within cells and pushes the leading edge membrane forward in moving cells.

Actin cross-linking proteins

Proteins of different lengths and flexibilities and F- actin–binding sites that organize different actin filament structures with specific functions.

Ezrin

Links actin filaments laterally to the microvillar plasma membrane and is activated by phosphorylation.

Myosin

Superfamily protein with a common head and specific tail domains. The crossbridge cycle converts ATP hydrolysis energy to mechanical work on actin filaments.

Myosin II

Skeletal sarcomere contractile unit which its actin thin filament–myosin II thick filament structure is stabilized by thin and thick filament associated proteins

Myosin V

Transports organelles and secretory vesicles along actin filaments.

Z disk

On each end of a sarcomere, shared with adjacent sarcomeres

I bands

Region of actin thin filaments, which are anchored to the Z disk by their (+) ends and extend from both sides of the Z disk into adjacent sarcomeres, that is not overlapped with myosin thick filaments.

A band

Myosin thick filaments interdigitate with thin filaments attached to the Z disks in each half sarcomere.

Sarcoplasmic reticulum

Regulates the level of free Ca2+ in myofibrils.

Troponin and tropomyosin

Regulate muscle contraction by blocking the binding of myosin to filamentous actin.

Cell migration

Coordinated activities in different cell regions.

Rho GTPase

Family of proteins that regulate formation of different actin filament organizations and myosin II activity to direct cell motility.

Step size in nanotechnology

The step size is 72 nm.